Cliff's Quadrajet Parts and Rebuild Kits
Quadrajet Problem Solving => Dialing in your rebuilt Quadrajet carburetor => Topic started by: don3194 on January 17, 2021, 01:21:58 PM
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So you guys may think I'm crazy for doing what I did, but its done and I'm having some problems with fuel economy. Basically the poorly designed fuel injection on my 1994 Oldsmobile Bravada failed so I found a manifold and installed this quadrajet I had lying around. I just used the walker rebuild kit from oreilly's to replace gaskets. So anyways my 4.3 quadrajet combo is getting only around 9 mpg in the city and 13 on the highway. I honestly believe I should be getting higher fuel economy, and my guess is that its dumping too much fuel for some reason. I also dont know if this quadrajet was from the 350 or 454 but from what I found it was off a 76' olds.
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What are you using for a distributor?
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I'm still using the stock distributor that came with the vehicle.
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Not sure what they used for a distributor but it would need a distributor that has mechanical and vacuum advance to work correctly if you have converted it to a carburetor from a TB or Fuel Injection system.....
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Okay. Well, I know it is a computer controlled distributor so it doesn't have vaccuum or mechanical advance. As far as I can tell it is advancing, but maybe not enough or too much.
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I can't see what you've done but the original set-up would have had a different intake and intake system, TPS, etc which the ECM would reference for timing/fuel delivery.
To effectively complete the conversion you may need to install a distributor with mechanical and vacuum advance or engine efficiency and fuel economy will suffer.....
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I can't see what you've done but the original set-up would have had a different intake and intake system, TPS, etc which the ECM would reference for timing/fuel delivery.
To effectively complete the conversion you may need to install a distributor with mechanical and vacuum advance or engine efficiency and fuel economy will suffer.....
Right now the ECM has enough input to properly advance the distributor, the vehicle drives and accelerates well enough, it just gets poor mileage.
I have noticed that when I go to start it, it smells like fuel and today I was just messing around with it, making sure I didn't have any vacuum leaks. Well, I pulled off one of the vacuum caps and the port was full of fuel. It was really only a dribble but I'm thinking this is related to my problem.
In the attached picture, my finger is under the port that the fuel dribbled out of.
If the image attachment doesn't work, I posted it here: https://imgur.com/a/O6Js6ki (https://imgur.com/a/O6Js6ki)
EDIT: Keep in mind that I had just got done driving it when I pulled that cap off, so it was at operating temperature.
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Your problems could be fundamental, starting with a poor quality rebuild kit with the wrong parts in it. I'd go back in with one of my complete kits, correct float setting, check the PP hanger arms for being bent, leave access to the APT system for full control of part throttle A/F, etc......Cliff
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Thanks for your input, I was thinking it would be something basic. How do I know which one of your rebuild kits to purchase? It looks like I have to choose between the Basic, HP and SR kits.
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Get the SR rebuild kit. It is a complete kit with all the parts required to do a complete/correct rebuild.
I would check the jets and metering rods to make sure they haven't been changed, modified, or just slam worn out.
I don't even look at them here, all carbs I get involved with get new ones. One has to realize that these carbs have been out there for 50 years or so. It's actually pretty common to see jets that have been drilled out to HUGE sizes and you wouldn't even know it unless you pin gauged them to check for size.......
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Okay, thanks. I'm friends with a guy who owns a machine shop, I'll ask and see if he has any pin gauges. What size for the jets should I be looking at?
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My listing skips that part number but it may be an early APT Olds unit with the auxiliary power piston.
If it has the second power piston and single metering rod it will have pretty small jets in it.
Personally I avoid those here. They had a very brief run and were abandoned for the far superior late style APT units, and for good reason.
1975-76 units with the APT in the left front corner (as viewed from the front) have fundamental issues related to the design.
The ones with the auxiliary power piston are the worse of the bunch.......Cliff
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Sorry for the delay, It does have a secondary powerpiston with a single metering rod on it. I actually just happened to pick up a decent looking marine quadrajet, 17059286, for $20. Do you think I should rebuild the one I'm currently using or maybe try rebuilding the marine carburetor?
(At least I think its marine, the Division number 8 seems to be unclear.)
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Sorry for the delay, It does have a secondary powerpiston with a single metering rod on it. I actually just happened to pick up a decent looking marine quadrajet, 17059286, for $20. Do you think I should rebuild the one I'm currently using or maybe try rebuilding the marine carburetor?
(At least I think its marine, the Division number 8 seems to be unclear.)
I thought about this overnight, and figured that I could probably turn around and sell this one and pick up a better automotive replacement. I just need an honest opinion, even though I think I know what it will be
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I would NOT for any reason use or attempt to use a Marine Quadrajet for what you are doing.
Get a later model side inlet Chevy carburetor preferably a single main airbleed model from a 1979-up truck application. They are e-choke or will easily convert to e-choke, and very well made units.
Most Marine carburetors were divorced choke, no APT, crappy hinge pin/float design, and calibrated for heavy loaded most of the time vs light load, fuel economy, passing emissions, etc.
Most will not even have a vacuum port for the distributor vacuum advance either. There are PLENTY of later model Q-jets out there and usually pretty inexpensive to buy as cores. Avoid anything "rebuilt" or commercially "remanufactured". I relatively clean and unmolested core will be best.......Cliff
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Thanks again Cliff, I have a friend I'm going to sell the Marine Quadrajet to as a spare for his boat. I found a 7043202 Quadrajet for very cheap and just picked it up. I know you said 79 and up but I just got it on a whim hoping it could be converted to e-choke. Just wanted to ask if this carb can be converted.
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No, the choke is on the intake manifold.
There are a few "conversions" available. One involves replacing everything on that side of the carb with a modified bracket/e-choke, and the other uses parts from a 70-74 Olds or 73-74 Pontiac and the main casting has to be drilled/tapped for the pull-off bracket.
I've seen a third using a modified 75-up adjustable choke pull-off and putting a later hot-air choke housing on the side of the carb. I'm not fond of any of those and it would be a LOT easier and less expensive to just source out a later model hot-air or electric choke carb right to start with.....IMHO.....
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To properly evaluate any carb it has to be at least renewed to factory specs.
Then it may need some help due to any symptoms shown at test drive.
A 4.3 Liter engine pulls less air than a 350 cui and the vacuum signal will be weaker making the power piston(s) rise at smaller pedal movements.
In the 17056250, early 1976 Olds 350 unit, the auxilary power piston spring is longer and stiffer than the regular power piston spring and may add more fuel than nessecary too early at low speed city driving for you 4.3 L.
The first attempt would be to use a weaker auxilary power piston spring, or cut to the same length as the regular pp spring.
I have done quite a few of these units, most of them got the auxilary pp system eliminated, 3-48 screw in jet and plug piston bore. APT is seated to start with and main air bleeds i bowl opened to .070". Most times #76-#77" jets with 52M rods are used. You always have the option to fine tune the APT. Also, an electric choke element makes the carb independent of intake styles.
HTH
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Thanks again Cliff, I think I'll just go ahead and resell what I bought. Also thanks Kent, I'll try and see if I can make a lighter spring for the auxillary power piston, otherwise I am interested in possibly eliminating it all together. Are you aware of any other threads with more information on eliminating the auxillary power piston?
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The aux PP and aneroid located APT carbs were short lived and for good reason.
Without going into great detail here I would NOT use one and source out a later APT model instead.
The 1975/76 models with that system just don't work well compared to the later models even after you block off the aux PP and single jet in the bottom of the casting.
I am NOT saying that you can't make one work, but it will never work as well anyplace as a later model set up with tapered metering rods that you can precisely position in the jets......FWIW......
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Alright, I found another good looking cheap quadrajet and I think this is like one that you suggested. Its a 17059222, I don't think its off of a truck and couldn't tell if it was single airbleed or not, but some quick searches on google found people saying it was a good one. Thanks again.
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17059222 is a good unit.
I would start with mounting .050" inserts in the current .120" main airbleeds, keep the original #71 jets and 40K rods. Set APT at 4.5 turns up from bottom then use "tip-in" to check/adjust.
Opening the .033" idle tubes to .036"-.038" will help the engine idling.
Optional, if off-idle hesitation occurs, would be to open DCR´s from .050" to .055" and the .080" idle needle holes to .095".
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Kenth are you referring to starting off on the 1709222? I just wanna make sure. Also if I do more reading up in Cliff’s literature will I find the meanings of some of the things you said. I’m not very familiar with Quadrajet’s or really any more recently designed automotive carburetor. I’ve only worked on a One Barrel off of a 1951 pickup before this one. I know APT, but I don’t know the “tip-in” method or DCR or how to do some of that stuff.
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The modifications Kenth describes help the later emission calibrated carburetor get adequate fuel to the engine.
Those are large MAB models and that particular one is set up pretty lean, but it's easy to tune and will work a lot better everyplace than the carb it is replacing.
If you call me at the shop next week I can set you up with what you need so it's pretty much "plug and play" for what you are doing......Cliff
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Alrighty, thanks again Cliff.
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Are there any detailed articles that explain the tip-in procedure for adjusting the APT? For that matter, where might I be able to find explanations on the proper initial settings for some of the adjustments that exist. Like the choke pull-off, the choke itself, APT, and maybe something else I am missing.
I have found some information floating around but some conflict and plain dont make sense, those did at least get me to a decent running engine with the 17056250, but on this 17059222, I want to have the best chance at getting it absolutely perfect.
Thanks
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There are "basic" settings listed in the instruction sheets and tech manuals for the choke pull-off, fast idle specs, etc.
Even so it is best to make ALL adjustments on the engine as the factory specs only get you close anyhow.
Here I use a mighty vac pump to apply the choke pull-off and set the open angle to make sure it doesn't choke out or flood the engine. I also adjust the fast idle screw to about 1200-1400rpm's on the highest step of the cam at initial start-up.
The fast idle and curb idles settings can really only be done on the engine with it running. None of this is fussy, but it may take several cold starts to nail down the ideal settings as the engine warms up quickly especially if you have a working exhaust crossover in the intake.......
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Thanks Cliff. I guess I'm really focused on the APT and I know that can take a lot of trial and error, but is there a procedure called "tip-in" for adjusting APT? I've searched around online and only found people mention it but not explain what it actually is.
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I just set them at 3.5 turns up from seated for initial testing. Gently "tipping in" the choke from with the engine running around 2000rpm's on the fast idle will tell you if it's rich or lean.
If it's lean the engine will speed up and smooth out slightly. If it's rich it will slow down instead.
That's really all a "tip-in" procedure is. Make sure the engine is fully warmed up and heat soaked when doing this test......
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Oh okay, thanks for explaining, that makes more sense.
I got it on the vehicle and started it up, at first it was running just fine, I was getting it warmed up to tune it and as soon as I started to reach in and adjust the idle mixture, a nice whistling/sucking sound started, the sound is very clearly heard from down the throat of the carb. It definitely is acting like a vacuum leak(idle is too high, and it responds well to a richer idle mixture), any idea where it could be coming from? When I get the chance to, I'll check my plug for the vacuum to the choke, but I haven't pulled it back off yet to look, but just thought I'd pick your brain for any idea on a sudden vacuum leak.
I did find another baseplate for it, this one actually had bushings put into it and its not worn out. The only reason I'm mentioning this is the possibility that they aren't compatible. The only difference I could note was two extra holes in the "new" baseplate that didn't exist in the original. I circled them in the picture.
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Are you saying that you swapped baseplates during the rebuild using one from another carburetor part number?....
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Well I think so, I don’t know what number it came off of.
I swapped it because I discovered that the one from the 17059222 was actually cracked around the primary shaft and very worn out on the secondary shaft. I thought I could just try it and hope those holes didn’t make a difference. I don’t think it did, but obviously it’s developed a vacuum leak somewhere and it could be related.
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It's supposed to be loose on the secondary side as the large throttle plates need some room to seal in the bores each time they close.
A crack means it was dropped at some point and doesn't hurt anything. Using my bushing install kit you can bore in deeper to install a bushing. I've done hundreds of them that were cracked and even had a chunk missing out of them.
In most cases the shaft is also bent and will need a little "tweaking" after the bushings are installed....
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When I say loose, I mean that the secondary shaft moves enough so the throttle plates will actually stick in the bores until the primaries reach wide open throttle, then they fly open.
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Upon some inspection I noticed that the gasket is not sealing the the middle, I can see where the gasket has been crushed in most of the areas but right in the center I can see where the air is seeping passed. Its right in-between the two primary bores. The gasket has no witness marks of being crushed but lines where I could see the air. I’m not too sure how to resolve this issue but neither baseplate seals it.
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Not possible unless someone put too much "monkey chit" (JB Weld or other useless epoxy for sealing up bottom plugs) on them to push the two parts away from each other. The main casting to baseplate gaskets are really thick and will seal up those parts without much effort.
I actually see that a LOT with carbs that come in here with those issues, either too much glue or the plugs they installed are too high. Most carburetors built after 1968 do not leak, but for some reason EVERYONE gobs tons of JB Weld over them, which woln't hold back fuel right to start with.....FWIW......
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Actually there is no epoxy or glue or anything on the plugs, which is why I'm confused too.
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I really didnt want to have to do this, but I think I will just re-bush the original baseplate. How much do your kits cost?
Unfortunately I think I need to do both the primary and secondary shaft bores.
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I'd leave the secondary alone. They seal tight on the large throttle plates and need a little room at the shaft to settle in each time they close.
You can order the primary shaft kit right off the website or call me at the shop, I'm here 7am-4pm, M-F EST...tks...
https://cliffshighperformance.com/product/5-16-throttle-shaft-bushing-kit
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Okay thanks, I’ll see how it works out after the primaries have the bushings. The fact that the secondaries were sticking in the bores worries me but I guess we’ll see.
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try adjusting the secondary throttle plates and/or checking to make sure the shaft isn't bent. make sure to grind the ends of the screws off so they don't snap off
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The throttle blades are bevelled so they wont stick.
I have seen "frankencarbs" with blades installed upside down sticking.
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Hmmm ok, well unfortunately I took it apart before I read this I so I guess I can't tell if that was the problem.
I am, however, unfortunate enough to have had the baseplate taken apart before (god knows why, they didn't even install bushings) and one of the screwholes is no longer a 3-48 sized hole. The threads are completely gone. Is it ok to resize it for a 4-40? Otherwise I'm kinda stuck.
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Go to 6-32 threads. I supply 6-32 screws with the bushing install kits for that reason. You'll also have to open up the holes in the throttle plates slightly for the larger diameter screws......
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Oh ok, I didn't know you supplied a larger size. I guess I feel better having even larger screws that 4-40 anyways.
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I installed the bushings in the original baseplate and reinstalled the carburetor with the original baseplate. It still seems to be leaking air from somewhere, its a lot better though. I actually have the idle just around where I want it, I'd probably want it about 50 rpms lower but the idle screw is backed all the way out. I can live with that but still makes me wonder what I'm missing.
I haven't rechecked timing, but couldn't too much initial advance artificially raise the idle?
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Check for too short throttle wire/rod holding the throttle blades open some.
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Yes, if the initial timing is pretty high on a "stock" or very mild application you can loose control of the idle speed.
EVERYONE doing this sort of thing will Google up the subject and switch or use manifold vacuum to the advance putting the initial timing WAY off the scale or at least 25-30 degrees or so. That's all fine if it works for you but some engines make a LOT of vacuum without much timing in them and adding a bunch more will have them idling too high even with the speed screw backed clear out.......Cliff
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I'd probably want it about 50 rpms lower but the idle screw is backed all the way out. I can live with that but still makes me wonder what I'm missing.
To further lower your idle, I recommend plugging your idle bypass air (IBPA). Just drill and tap the throttle plate and install some 1/4-20 setscrews. There are pics of this mod on the internet. This trick allows using carbs from larger displacement 350 engines on smaller motors like your 4.3 V6 or a 305 V8.
Once IBPA is plugged, you will have control of your idle screw. This will allow you to open the thottle blades just enough that these are not sticking in the primary bores. I'd bet with the idle screw backed all the way out, you currently have a bit of stick/slip when first applying throttle.
By the way, the IBPA is probably your mysterious vacuum leak. That's what it is, a controlled vac leak used by Rochester to raise or lower the idle so that the idle screw works within a small window. The range of usable idle screw is from blades fully closed to thottle angle which begins to draw fuel from the transition slots. So, fairly narrow range, hence the IBPA.
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Okay, I verified timing, verified my throttle cable isn’t restricting. The throttle plates are all completely closed. I blocked the idle bypass port you suggested to block bry, and that made 0 change whatsoever. I’m baffled that it didn’t change anything. The idle will not go below 800 rpms, I can live with it being 50 higher than where I’d like it but I mean it shouldnt run with the blades sealed.
One thing still to note is that I can hear a nice whoosh/sucking sound through the primaries at idle.
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Did you block the idle bypass air on both sides?
If you don't have idle bypass air and all the throttle plates are completely closed at idle you should have full control of the idle speed and it will go below 800rpm's. The engine has to be getting air someplace?
The "whooshing" sound thru the primaries sounds like it still has bypass air and is "whistling" past the entry slots in the airhorn where they lead to the voids in the main casting......
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Double check the thick gasket between your intake manifold and carb base. I once used the wrong gasket and a bit of the front edge of the carb overhung the gasket causing a substantial vacuum leak. Don't recall if I used a 170 series on a 70 series, but it was something like that.
The IABP ports are shown on your baseplate pic. These round holes are to the left and right of your circled as cast ports. I think you'll find those as cast ports deliver vacuum to different ports on the exterior of the carb.
Double check all your exterior ports to make sure these are plugged. For non-emissions, all you need are four ports:
- Choke Pulloff
- PCV Valve
- Full-time Vacuum (for "manifold" vacuum advance)
- Ported Vacuum (for vacuum advance except at idle)
You might also need the NPT port at the back to run your power brake booster.....
I ended up pulling the pressed in nipples (vice grips and a torch), and then resizing the holes to fit aluminum rod (3/16, 1/4 and 3/8). I cut the bar stock to appropriate lengths, coated the OD with red LocTite and tapped into place. This really cleaned up the looks of my 170 series carb and will never leak (unlike rubber or vinyl caps that will deteriorate).
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I did block the Idle Air Bypass on both sides, following this picture http://www.wallaceracing.com/Adjustable_bypass_with_wrench_small.jpg (http://www.wallaceracing.com/Adjustable_bypass_with_wrench_small.jpg) from this thread https://cliffshighperformance.com/simplemachinesforum/index.php?topic=2587.0 (https://cliffshighperformance.com/simplemachinesforum/index.php?topic=2587.0) I know all of my external ports that I'm not using are plugged for now. I did verify my vacuum advance is on a ported vacuum source. The only thing you mentioned that I didn't check was the intake to basplate gasket.
The gasket is one that Cliff sent so I've gotta assume its right, but I suppose I can check when I get the chance too.
I suppose I also could have blocked the wrong holes too.
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If you blocked the bypass air and all four throttle plates are tightly sealed when closed (idle speed screw backed off) then the only place it's getting air should be at the PCV valve.
If you have a leak someplace, power brake booster, intake gasket, carb to intake gasket (unlikely if you used a pretty thick one) then the engine can get enough air to idle with the throttle plates fully closed.
Most of the carbs I get in here for rebuilding do NOT close the primary plates all the way in the bores and require some "tweaking" with the linkage to make that happen......
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The PCV is a vacuum leak by the very nature of its design. I seriously doubt if you have plugged the IABP and the idle is still high, that your PCV is the culprit unless the body is cracked or something odd like that.
As for the brake booster, I worked on a friend's car that had a high idle. He had removed the quad and put on an AFB to try to fix. I simply plugged hoses until the idle changed with the brake booster hose. I put the quad back on and fixed the booster. By the way, if the booster is leaking, you will have to push abnormally hard on the brake pedal.
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Well, when I get chance I'll check the gaskets and vacuum acessories. The only things that are hooked up directly to the carburetor are the distributor and the the vacuum cannister. I will recheck it, but those two items I did not have hooked up and still had the problem. I know my brake booster is going bad but I do not believe it is the problem. I will not eliminate it as I have not rechecked it since I noticed the high idle.
I also did verify my throttle blades do completely seal.
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Another thing to look for is intake manifold gaskets. If the gasket is leaking to the outside of the engine, it is much easier to find. Usually, you can start the engine and let it idle. Then pour some water on the intake manifold, along the valve cover and wait to see if the idle slows. If it doesn't, try the other side. I like this method because it is not flammable, nor does it dissolve your engine paint.
Internal vacuum leaks are more tricky to flush out. I've actually plugged the valve covers and put a vacuum gauge on the dipstick tube. Using this method, you should see pressure build as piston ring blow-by slowly pressurizes the crankcase. If you see vacuum, you definitely got a problem. If you see no change, then your engine is not well sealed.
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Another way to find a leaking intake gasket is to let the engine idle and one by one pull a spark plug wire from the cap. If it's leaking on one runner, which happens on occasion you will not get nearly as much engine miss-fire/RPM drop when that plug wire is removed at idle speed.
Until I outfitted my current 455 with the large port Felpro "blue" gaskets (steel core) for the Super Duty 455's I had 3 different sets of aftermarket large port gaskets fail. Each time they started leaking at one intake runner. It took a few years for each failure, but it was difficult to diagnose other than a slight miss-fire at idle speed.
I found the problem by gently removing one plug wire at a time from the distributor cap and listening for a miss-fire or pretty decent engine speed change. When I got to the cylinder with the leaky gasket the change in RPM was very minimal.........Cliff
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Well, I sure hope its not my intake gasket. I did just do those about 4 months ago. I haven't had a chance to get out and do any more diagnostic work, but I think tomorrow I can eliminate more possibilities.
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Idle still seems high after removing every vacuum operated item and capping the ports.
I do have a question though, when performing the tip-in procedure, should the power piston be seating as far down as the APT screw lets it?
I found that when I revved the engine up to 2000 rpm's, the power piston still seemed to be in an upper position. To adjust the APT I had to push it down and seat it through the vent so the APT adjuster tool didn't get caught on the pin sticking out of the power piston.
If it also helps I've driven it around a decent amount and found I get 11.5 mpg city and maybe 12 on the Highway. Those two numbers being so close is suspicious to me.
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The Power Piston should be all the way down when the engine is running and you are adjusting it.
The vacuum at idle, off idle and even up at 2000rpm's would be high. The only time you can drop vacuum low enough would be hitting the throttle really quick and vacuum will only drop momentarily allowing the spring under the piston to raise the PP for just an instant.
IF the PP is up at idle, off idle, or even at 2000rpm's light load you have another issue someplace.
Start by checking the hole in the baseplate to make sure it's drilled all the way thru and not plugged or blocked off.
Check the power piston to make sure it isn't tight or sticking in the bore. It should move up/down easily without any resistance. The retainer can also interfere with it's travel, so make sure it's correctly installed on the PP and not impeding it's movement.......Cliff
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Idle still seems high after removing every vacuum operated item and capping the ports.
should the power piston be seating as far down as the APT screw lets it?
To adjust the APT I had to push it down and seat it through the vent so the APT adjuster tool didn't get caught on the pin sticking out of the power piston.
1. If your idle is still high, and you closed off the IABP, then yes... you probably have a vacuum leak. Put a vac gauge on it. The needle movement will help diagnose the problem. There are tutorials on the net to teach what the needle is saying.
2. The power piston should be sucked down against the top of the screw, regardless of how far down the screw is. If the piston feels springy at idle, then the spring is too stiff for your cam vacuum (it should be down). You need to switch to a weaker spring.
3. Did you really have to push it down? You can feel it go up and down with the engine off? Did it go up and down with the engine running? If so, see 2. But yes, the APT tool will tend to get hung up on the piston "pin" unless you hold it a little high so as not to get the pin caught in the tool.
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Yours 17059222 have the 8-4 in/hg power piston spring from factory, which means it starts rising the power piston at approximately 8 in/hg and is fully up at 4 in/hg.
And, with APT screw bottomed it will take 2 full turns of the screw to reach the lift pin on the bottomed out power piston before it rises the power piston at all.
With engine off, check movement of power piston thru the vent hole. Does it move down when pushed on, does it returns upward when you release it?
With engine running at operating temperature, check intake vacuum, rpm´s in and out of gear (A/T).
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Hey all, I found the hole was NOT drilled in the baseplate. You may or may not agree with what I did, but it worked. I compared how the holes were on the other baseplates and drilled this one out. And it made a huge difference while driving. The power piston is being sucked down now.
As for my idle problem, it still exists, I have attempted a vac gauge on it, but it honestly looks like a perfectly healthy engine (according to the gauge). Nice solid steady needle, no erratic movement.
Another thing I just want to inquire about is, whenever I lay into the throttle, enough to open the secondaries, I hear a weird rattling type sound. I'm not too experienced when it comes to sounds like knocking/pinging or other engine sounds, but it honestly sounds almost like metal against plastic. Its not very loud, but noticable. It sort also sounds like something in the carburetor is rattling.
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pcv valve? what brand are you using here?
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I have attempted a vac gauge on it. Nice solid steady needle, no erratic movement.
Since you have blocked IABP, rebushed the throttle plate and still have high idle here are a few other suggestions:
Make sure your throttle stop tang is bent properly to allow full closure of the primary blades.
How many turns out are your idle screws?
What is your float measurement? Maximum 3/8 if no fuel regulator.
What size needle seat are you using? Maximum .135" for trouble-free daily driver.
Whenever I lay into the throttle, enough to open the secondaries, I hear a weird rattling type sound. sounds like something in the carburetor is rattling.
Detonation usually has a tiny, pingy sound. Like bb's bouncing around in your cylinders. Heavy detonation can sound like a rattle. If you are using a Chinese distributor, most have no limit on the mechanical advance curve and advance well past 32 total. This will cause serious detonation. The solution is to limit the mechanical advance with heavier springs or a mechanical stop. Better yet, hit a swap meet and pick up a used GM distributor. The old HEI were well designed and usually only need lubricated, new weight bushings and lighter springs to wake 'em up.
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The float level listed above should be a minimum of 3/8. It will work fine between 3/8 and 7/16.
I bet it does drive a lot better if the power piston was never rising. That will cause a lean hesitation whenever leaving a stop light or during moderate acceleration. This assumes your throttle angle results in sub 8 in Hg. I noticed my truck leaves a light at about 10-6 in Hg. And when my spring was not lifting the piston, it hesitated and I had to flutter the throttle (add fuel with accelerator pump) to get it going.
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Hey all, I found the hole was NOT drilled in the baseplate.
Then it was from a turbo carb most likely
CCC carbs aren't drilled either, but they are slightly different in other areas like using a much thicker rod up to the accl pump arm, etc.
Your PP spring should NOT be a player for "normal" driving at light load. Heavy load or quick throttle movements yes. Any heavy or load applied quick enough to DROP vacuum below about 10" or so will also retard the timing as the VA will also come out of play.
I've logged many thousands of miles custom tuning with a vacuum gauge rigged up where I could see it and it's rare to see vacuum fall off much at all at vary light engine load. Most will actually be higher than they were at idle speed, unless you push down the throttle pretty quick and heavy. When this happens the accl pump is there to cover a momentary lean condition until the carb increases fuel delivery accordingly.......Cliff
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Just to put this part to rest right now, my PCV is not hooked up at all right now.
Its been a while but want to say I set my float level at 13/16" but again its been a month or so and I just cant remember for sure. I do have a fuel pressure regulator set to about 5-6 psi.
I dont know what size needle seat it is, Cliff sent it in a kit for a 17059222.
Where is the tang located, I mean having the carburetor off I can see that the blades close but I just want to check everything here. I can back the idle screw out until it is not touching.
I think my idle mixture screw are out in the range of 3-4 turns but I cant remember that either.
I also just want to say again that I remember when I first put this carburetor on, it had a good low idle and then something changed, a sucking sound started and the idle went up.
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If the idle screw can be backed out until not touching, that part of the equation is okay.
Idle mix screws at 3-4 is about right. So, nothing unusual there.
You are not blowing the needle off the seat and adding too much fuel if regulated to 6psi. So no problems in this area.
A sucking sound could be a problem. Another way to hunt down a vacuum leak is to take a length of vacuum tubing and hold one end to your ear while moving the other end around the carburetor base, manifold edges, etc.
If you had good low idle and then something changed, that had to be something you did. What did you change? Was this before the rebuild?
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Well see, the sucking sound started while it was running. I had just got the engine warmed up after the rebuild and was about ready to start adjusting the throttle screw. Quite literally, I touched the tool to one mixture screw and I heard the sound start and the idle went up.
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If it wasn't doing it and then all of a sudden, with the engine idling, a sucking sound started and the rpms increased.... it sounds like a gasket was barely sealing, and then the idle vacuum was enough to unseal it. Again, carb to intake gasket would be suspect as that is an easy one to hear. Another possibility is the airhorn gasket since you can hear those leaks as well. If your carb body is smashed down at the front two mounting bolt holes, then possibly the airhorn gasket is leaking slightly. Obviously, both of these would make your idle lean, and would require additional turns out on the idle mix screws to add more fuel to make up for the extra air. More air + more fuel = faster idle.
You'd be surprised how loud a vac leak in the carb is. Simply opening idle air bypass (IABP) from .052 to .100 makes a very obvious sucking/whistling noise.
By the way, to tell if the airhorn gasket is leaking, you have to remove the airhorn and check the gasket for witness marks caused by the raised ridges on the top of the carb body. The ridges trace around anything that must by 100% sealed. So, if any part of the gasket is not showing these witness marks, that would be a suspect area.
Another thing that might make a sudden "sucking sound" is a ruptured diaphragm in your choke pull off. Put a hose on the port, suck on it and block the end of the hose with your tongue. If the vacuum bleeds off, then you have found your problem.
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Well I'm kinda feeling like an idiot, but I guess I'll just say make sure you use the right timing mark on your harmonic balancer.
As far as I could tell there was only one, but come to find out there are a couple on there. I'm not quite sure what the purpose of the one I was using is, but I retimed it to the right one and now I have the idle screw turned in about a 1/2-3/4 turn, there may still be a problem because the sucking is there and blocking the IABP didn't do anything.
Anyways it seems to drive well, the only thing is that if I go and floor it, it bogs down quite a bit at lower rpms once the air doors open.