Cliff's Quadrajet Parts and Rebuild Kits
Quadrajet Problem Solving => Dialing in your rebuilt Quadrajet carburetor => Topic started by: D Denzin on March 15, 2015, 09:03:05 AM
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I can't get my Rebuilt Carb to Idle decently.
It surges. When it Idles at lower speeds it seems labored. It is inconsistent idling. Speeds up, drops down runs rough, if I blip throttle it'll idle faster, eventually will idle down and resume rough idling and surging. I have to adjust Idle screw out like 3 turns to get it to stay running. Then it runs at about 2000rpms before it seems to smooth out.
Specs.
Pontiac 65 326 HO with 9.2:1 comp.
Cam is basically very close to stock.
carb 17057253
Engine is rebuilt a couple of years ago. Switched carb from original AFB and Intake to Q-Jet and Edelbrock alum intake.
Car ran good with old set-up.
Was rebuilt using kit from Cliff and his recommendations about a year ago. I haven't had the time to mess with it until lately.
Jets .073
Metering Rod .044
Idle Tube .034
Idle Down channel .043
Upper Idle Air Bleed .070
Lower Idle Air Bleed .070
No holes in throttle plates
Idle bypass Air .081
Holes under Idle Mixture screws .090
Air horn Air Bleed .070
Main Body Air Bleed .029
I have checked for Vac leaks with a unlit propane torch. I have disconnected Dist Vac advance. I have disconnected Vac Gage supply. All with no effect. I even supplied propane into the disconnected open vac supply for the gage and it made no diff. Right now I have mixture screws out 2 1/2 turns. Adjusting them in and out has minimal effect. They will cause the engine to get rougher if I screw them way in. I have adjusted the APT in and out thru its full range and it seems to help being set almost all the way out.
Any Ideas on Where to go?
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sounds like you have too much idle air possibly. With the idle bypass and .034 in the tube.
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Trying to understand, too much idle air.
I can't get it to idle at all unless I open the throttle blades by turning the idle adjustment screw on the throttle linkage about 3 turns. My eyes are burning at times from the exhaust, thought that was a symptom of too rich.
the best I can get is by turning apt all the way up.
Any easy way to test if I have too much idle air?
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Big improvement. I disconnected the PCV hose from the carb and capped it. WOW. Now i can get it to idle down to 750-800.
I reconnected the dist advance to the manifold vac. source on carb.
I can adjust the idle speed down using the screw on the throttle linkage to the point that its not even touching.
At that point I tried to turn in the mixture screws to get the idle down. Still can not get the idle down before the engine starts to surge, run rough and die.
When adjusting idle mixture screws and even idle speed it seems odd in that I can make an adjustment, I can see a response in a second or two, then in about 5 to 10 seconds the idle will continue to deteriorate surge and get rougher and rougher. I can blip the throttle 2-3 times and drop it back to idle and it'll be fine for about 10 seconds or so. Then it continues to get worse till it will eventually die.
So now I'm at the point that it will idle decently, a littler faster than I'd like, for about 10 seconds, if I let it sit it eventually will die. I can speed up the idle to about 1000 and it will stay running but then its idling too fast.
Any thoughts?
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id say your float is ether set to high or your needle and seat are leaking ,or your seal on your seat is leaking . what your saying is you are flooding at idle? did you get the gasket under the seat nice and clean before you installed the new one?and did you install a new gasket under the seat. i hate to ask these questions but one little spec of crap will cause the problems you have. do you have a choke is the pull off working?is the choke wide open?fwiw
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Sounds to me like the intake getting air from somewhere with the throttle blades closed. First I'd check to make sure there is play in the linkage rod on the driver side that goes from the primary to secondary throttle shafts. No play could mean it's holding the secondary throttle plates open a hair at idle. If no help there I'd plug the .081 idle air bypass. A 326 with stock cam wouldn't need it IMO. Also I'd check to be sure your distributor vacuum advance can doesn't have a vacuum leak and also that the carb choke pull-off doesn't leak vacuum. Plus, I've seen Q jets where the choke fast idle screw (down low on pass side) is adjusted too far to let the primary throttle blades close enough for warm idle. Try backing it off (counterclockwise) a little.
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id say your float is ether set to high or your needle and seat are leaking ,or your seal on your seat is leaking . what your saying is you are flooding at idle? did you get the gasket under the seat nice and clean before you installed the new one?and did you install a new gasket under the seat. i hate to ask these questions but one little spec of crap will cause the problems you have. do you have a choke is the pull off working?is the choke wide open?fwiw
I'll check on the needle and seat tomorrow. I have a electric choke, its seems to be working, closed when cold, engine runs on a faster idle, opens up as engine warms. Choke is wide open when warmed up fully. Thanks for the ideas, will check and report back.
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Sounds to me like the intake getting air from somewhere with the throttle blades closed. First I'd check to make sure there is play in the linkage rod on the driver side that goes from the primary to secondary throttle shafts. No play could mean it's holding the secondary throttle plates open a hair at idle. If no help there I'd plug the .081 idle air bypass. A 326 with stock cam wouldn't need it IMO. Also I'd check to be sure your distributor vacuum advance can doesn't have a vacuum leak and also that the carb choke pull-off doesn't leak vacuum. Plus, I've seen Q jets where the choke fast idle screw (down low on pass side) is adjusted too far to let the primary throttle blades close enough for warm idle. Try backing it off (counterclockwise) a little.
I already checked the linkage rod from the secondaries to the primaries, OK there.
I'll look into all the other suggestions that are "easy" checks and leave the plugging the Idle Bypass till last.
I'll check into the vac advance, I did check operation before putting dist in by applying vac to be sure it worked, to be honest didn't check to see if it would hold and not leak down. Also checked the choke pull off but again for operation not if it held with a leakdown.
I'll check the screw on the choke to be sure its not holding up the primaries.
Thanks for the suggestions will check tomorrow and report back.
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429bbf,
Checked float level, was 9/32, changed it to 13/32 as spec'd in rebuild sheet.
Disassembled seat and checked gasket and mating surfaces. All looked good reassembled.
I don't have the degrading idle anymore. Your excellent advise on checking float level helped.
Von,
Secondary to primary rod was OK as I mentioned before, so I plugged the .081 Air bleeds.
I also checked the the vac advance and the choke pull-off. Both held vac without leaking down.
I also backed off on the choke fast idle screw, it wasn't touching, made no difference.
So now I can get it to idle down to 680-700 with pvc attached and vac advance attached to manifold vac. Idles very nice and smooth. If I slowly work the Idle mixture screws in it won't reduce idle, just degrades it till the engine runs rough and dies. I can back the idle adjustment screw on the throttle blades all the way out and the slowest idle I get is 680-700.
If I pull the PVC it will idle down to like 550 or maybe even less. If I pull the vac advance and plug or switch it to the ported vac source I can get the idle down. But the idle is rougher.
The timing is set at a total of 34 deg all in. Intial timing is 12 btc. When at Idle with vac advance on man. vac I get about 24 total at the 680-700 idle.
I'd like to get the idle down to about 600-625. I can do it with no PVC or ported vac for the dist advance but then the idle is rougher. Seems like idle is lower cause the engine is struggling. Maybe I should work on getting a better idle quality using the ported vac. At 680-700 with vac advance on man vac and pvc attached the idle is silky smooth. I'd just like to knock it down about 75 rpm's.
Von, I think your suggestion of plugging the air bleeds helped knock the idle back about 100 rpm's. Thanks!!
Anymore ideas to help me over the hump?
Thanks both Von and 429bbf for your help so far!!
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Are your throttle plates adjusted evenly? You might try a different PCV valve some have different ratings for the amount of air they pass.
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I looked at the throttle plates, the secondaries close nice and tight. Primaries look good too.
I bought a new PCV and tried it. No Difference. I messed around with moving it from the primary side of carb to rear then from there to the intake. None of these location seem to matter. I didn't think they should but I tried. I'm going to move the PVC back to the front of the carb. I guess I'll have to run to town and pick up a couple of different pcv's and try them.
In the big picture it seems as I'm getting too much air somewhere. I'll have to take a second look at everything.
I checked for vac leaks with a unlit propane torch, any better way?
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i use starting fluid to each his own . i agree with jim on the pvc i used to think they were all the same but there not. pull the pvc out of the valve cover or where ever it goes and leave it hooked up. put your thumb over it and slowly start restricting the vacumn and see what happens . hth you may also try plugging all the other vacumn lines ,brakes ,trans,etc. you never know where the problem is.
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I pulled the carb off Sunday and took a real good look at the base plate. No, the throttle plates don't close perfectly tight. By that I mean they close tight, can't close them up any more but You can see light around them if you hold them up to the light. Its a issue that the plates are a couple of thousands smaller than the bore side to side. I looked at some older unrebuilt carbs and they appear to be air tight but after cleaning the carbon and soot they have the same gaps. Not much can be done about it.
I had some other issues (leaking water pump) that I needed to fix. In the mean time I ordered a couple of different PCV's that I'm going to try. Not much in-stock in town.
I am only tapping the Q-jet for Vac for the PCV and Vac Advance for the dist. Car has manual brakes, manual trans.
I also drained the gas tank as the gas for the most part was over a year old. And I am replacing the add on fuel filter that was in between the pump and the carb. The filter looked to have some "milky" looking gas in it. Taking no chances.
So I have to wait for the PCV and fuel filter I ordered.
I also Changed the carb to intake gasket. It was a open one, I swapped it out for a divided one. I don't think it'll matter but it won't hurt.
Am trying everything I can think of.
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Are the throttle shafts tight?
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Throttle shafts are good. I rebushed the primaries using Cliffs Kit.
The secondaries aren't tightest fit I've ever seen.
I have checked and watched to be sure that the primaries always settle back to the same spot and I have tried to turn the primaries while running to be sure that they always seat back to the adjusting screw. No issues there.
I could try putting grease around the secondary while its running to see if that helps.
I'll put it on my list of things to try.
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The primary throttle blades must be installed one way only. Did you mark them before removal? Also the secondary blades have beveled edges and must be installed in the proper orientation too. If you installed everything exactly as it came out, it's always possible someone incorrectly installed them in the past.
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The secondary throttle plates need to be correctly indexed, centered and closing fully so you don't have any air leaks around them. The factory used a pretty "loose" tolerance on the secondary throttle shafts so they can return to fully seated each time they close. It's a pretty important part of the rebuilding process, so spend some time with the secondaries to insure that they are fully seated each time they close.
It's not uncommon to find a shaft that is twisted slightly, linkage holding them open slightly, or the plates not correctly centered up and indexed so they fully close. If not done correctly, they are a vacuum leak and will not allow the engine to idle down low enough, and leans the idle mixture out at the same time.....Cliff
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How tight are the secondary blades supposed to be. They look good. But if you hold them up to the light there is a gap around them. There are touching on the higher side (higher up in carb). If I had to guess I'd say there is less than .003 gap. Any person with decent eyes can easily see a .001 gap with light behind it. You can see that they are narrower than the bore. So no way will they ever seal closed completely. Maybe I should take a feeler gage and check the clearance. I'm sure its very little.
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Ok, here is where I'm at.
I have fresh gas in the tank, I put in a new in line fuel filter.
I pulled off the carb and got out a feeler gage and checked the secondary bores. There is a small amount of movement left to right (side to side) of the butterfly shaft and butterflie assembly in the bores, its no more than .0015. No more than .0005 (that's right 1/2 of .001) of gap between the bores and the butterflies front to back when they are closed. I am sure that the fit of the secondaries to the bore is good.
I have to run the car with the PVC plugged.
At this point my idle is still poor. It isn't smooth, its a little rough, not real bad, but it has been better.
I can get it to idle at about 650. But what it does is it'll idle there for about 10 seconds then it drops down to about 500-550 for a second then it speeds back up to 650 and it'll idle there again for 10 seconds and it then repeats.
If I adjust the mixture screws out a half turn it'll loose the speed changing but then its idling at 700. I then back off the idle screw at the throttle linkage about 1/8 of a turn and then the idle drops but I'm back to the idle changing speeds. I started out with the mixture screws out 3 turns. I kept repeating the adjustments now I'm out 5 turns and nothing seems to be improving. Eventually I'm at the point again that the idle adjustment screw is not touching the throttle linkage. If I start cranking in the mixture screws then the idle gets real rough.
I don't see any dribbling of gas going on in the primary bores by the booster rings while its idling.
Any thoughts?
Thanks for all the help so far.
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Must keep the PVC plugged. Just a thought but are you using power brakes?
If so could you be loosing vac thru the brakes?
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No power brakes, only VAC. hookups on carb are the PVC and the Vac advance for the dist. Manual trans. Very simple setup.
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Part of the trouble here may be too lean at idle. Going back and looking at the idle tube size and DCR's that's a pretty lean set-up.
How far out are the idle mixture screws set at? Do you have full control of idle quality from rich to lean using the mixture screws?
Check the timing as well, and make sure it's rock solid steady at idle speed.
How much vacuum does this engine produce at idle speed?....Cliff
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I read Cliffs last post and decided to go out and see if I can see a difference if I adjust the idle mixture screws out. I know if they are too far in they will kill the engine so thats too lean right?
So After the engine warms up I adjust the mixture screws out 1 more turn. Now at 6 turns out, was at 5 turns when I started the car. Car is still idling. I crank out the screws another turn. 7 turns. I'm thinking 7 turns out thats pretty far. I let it sit and idle. Seems if anything its idling rougher, slightly. So I adjust it in to 6 again. Idle does speed up a hair and does smooth out a hair. Is that now too far out? Is that what I would see if its Too rich? I guess I'm asking the question how do I know if I'm too rich?
So in answer to Cliffs question "do I have full control of idle quality from rich to lean using the mixture screws?" I don't know. I'm not a wizard on these things, I'm very mechanically inclined but my knowledge is lacking. I'm asking the question back "How do I know if I'm too rich? and "how far out can I go with the mixture screws?"
"check the timing as well, and make sure its rock solid steady at idle speed"
My answer to this. It is if the idle is steady. I have the dist advance attached to the man vac source. If my idle is floating around, man vac is floating so is advance. Should I maybe working on idle without using any vac advance? Plug both manifold and ported sources and then adjust idle? Again initial timing is 12 and total is 34, at idle its about 24 with manifold vac attached.
"How much Vac does engine produce at idle speed?"
At 700 rpms I get a good 16-17 inches.
When the engine idles at 450-500 its 12 inches, at 600-625 its 15-16.
Here is the kicker. From my last post on March 25 where I describe where I'm at things have changed.
Now I can get the idle down. What I did to get this change? I don't know, I walked away for a day, went fishing and gave it another try. When I came back it changed. What I do is adjust idle to 600-625, I get a 15-16 inches of vac. But the idle sort of floats up and down that 25 rpms. If its idling at 700 its rock steady. At lower speeds it sort of floats very little. Not to worry?
Now when I shut off the engine and restart it the idle is at 450-500. I don't have touch anything for it to start. I'm standing out side the car, reach in the window, turn the key off, then engine kills, no dieseling or anything. I can count to 10, touch the key to start the engine, fires right up but its idling real slow. If I blip the throttle up and hold it up so its running at 1000-1500 rpms for about 1/2 a minute and drop it back to see what the idle is. Then the idle might be about 550-600. So if I adjust the throttle screw just a hair. And I mean its just a very fine adjustment, less than 1/8 of a turn on the screw, just barely turning it and the idle is again fine. 600-650.
I turn off the engine again and restart its idling 450-500 again. I can get the idle back to the 600-650 by running the engine for along period of time at an increased speed.
What is going on here?
If anything this car is consistent in its inconsistency. If that makes any sense. I mess with it. I think I know where I'm at. I go away, come back and then its doing something else. At first I couldn't get it to idle down. Now it idles down, I can get a decent idle, at least I think so. But if I try to turn the car off and restart the idle is bad and needs adjusting.
Is 10 seconds of sitting enough to cause some sort of heat soak? or is the vac being shut off completely then coming back causing something to change. Is something maybe sticking somewhat in the carb and when I shut off the engine and vac it moves causing the really slow idle?. Maybe I should fix up the other couple of minor issues I have with the car and take it out and drive it. Right now its not drivable, seat is out. Everything I've done is just been done in the garage. I probably have a couple of hours of run time in the garage.
I'm still running with the PCV plugged.
Please don't give up on me here. And don't feel like your going to insult me by asking what to you are insignificant questions. Like I said I'm no wizard on this stuff. But I am perfectly capable to fix this if I can get some direction/knowledge from some more informed sources. I'm just at a point I don't know what to try next. Maybe I should go fishing again and it'll be better. Maybe there are some sort of garage gremlins messing with me.
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At what rpm are you checking the timing? If at 600 does it change when you bring it up to 700 rpm? If it does your spring are to light for the mechanical advance.
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+2 on checking the timing. Inconsistencies in idle speed and idling too slow after a restart are often distributor related, or inconsistent timing.
Hook the PCV system back up. Millions of engines used that system, it needs to be there to keep the engine cleaned out. Figure out the issues with it in the system working like it's supposed to.
Your problems seem to me like to much timing at idle combined with carb a tad lean at idle speed. You should have full control of the mixture screws, are better sensitivity with them without backing them out so far.......Cliff
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Most carb issues are actually ignition issues!!! That is a true statement I learned a few years ago.
When I had my DUI HEI curved I had them setup curve to start at 900-950rpms. This worked wonders
for my idle in and out of gear. And running ported vacuum advance takes another variable away from
idle equation.
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Well I pulled the dist apart and found it had apparently the wrong weights in it. I checked them against an old dist I had laying around. So I swapped them out. Car ran better. I ended up reattaching the PCV and swapped vac advance over to the ported source. Car ran OK. I turned car on and off. Everything seemed better. No changes.
I figured I check total timing, adjust mixture screws using the vac gage and do any final adjustments.
I thought I had it licked.
While I was getting my stuff ready to restart and do the adjustments I notice there is smoke coming off engine on the pass. back corner. Where the PCV goes into the Valley cover. I figured something was screwy with the PCV. Well long story short it seems the coil was leaking oil. I could see oil bubbling out of the rolled seam on the top of the coil. This was causing the smoke. I pulled the coil and appparently the black plastic top section is bulged and cracked. Its also low on oil. You can hear the oil sloshing around when you tilt the coil over.
So now I need to get a new coil. I was using a Pertronix coil to go with the Pertronix ignition set. I'm going to get my hands on a old GM coil and try that. I might be able to prevent a new pertronix coil from going bad if I remount it up and away from the engine but it seems that the original GM stuff lasted in the original location why shouldn't the aftermarket one? Off to find a coil and try again.
Thanks again all for helps and tips. I'm optimistic that I'll have this licked soon.
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Progress is a good thing. The distributor is a big player with these things, and you've got to get it working correctly before carb tuning will be effective.
You didn't mention if the timing was actually moving around at idle speed or not?
I would also check the mixture screws now that you have went to a ported source, to make sure they have enough fuel for the engine without backing them out too far?.....Cliff
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Timing is solid. doesn't move around at idle when using ported or plugged. Moves slightly when idle is fluctuating when I'm using manifold vac source. Centrifugal advance does not kick in till around 1200 rpms.
Mixture screws were turned in about 2 turns on ported vac. Seemed to help smooth out engine. I was going to do some final adjustments as mentioned in last post when I noted bad coil. So thats where I'm at now.
Thanks for all the help. I'll advise what happens when I get a new/different coil.
Always seems to be 2 steps forward one back.
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So I got a new coil.
I can get it to idle at a decent rpm. 600-650. That's good.
It doesn't idle smoothly, kinda labored. I get about 13-14 in. of vac at idle.
I've got timing at 13 deg at idle. Ends up giving me about 35 total with no vac advance. Am using ported vac source for dist.
I've got the PCV hooked up.
I've got the mixture screws out 7 turns. Seems best about there. Not a lot of difference in the adjustments of the mixture screws. If I get them in too far, maybe 2 turns or less it really gets rough. I can crank it out and all it does is increase the idle speed alittle. Does not really make the idle smoother. So then I adjust the throttle linkage to lower the rpms. Shouldn't I see more of a dramatic difference in adjustments on the mixture screws? How far out is too much? how do I tell if its too rich on the mixture screws? I'm hesitant to go beyond 7 turns out. There is no resistance from the springs at this point and the mixture screws seem very loose.
So all in all its idling at a decent speed but its idle is not smooth, minor surges and it floats up and down between 600-650. The Vac is lower than I think it should be and it too floats between 13 and 14 in. I checked the timing with the vac advance disconnected and plugged. Timing is solid. Removing the vac advance does not change the timing as I would expect it shouldn't when using the ported vac source. When adjusting timing I notice that the engine speeds up and smooths out when advancing the timing to about 20-25. Why not go back to man. vac for the dist advance? If there is no downside that anyone can clue me into I'm going to try that.
I got a couple of other issues fixed while waiting for the coil so I could take it for a spin down the road. Seems to run pretty good. No bucking, secondaries open nicely. I would say that other than the idle this carb seems like an improvement from the stock AFB that was on the engine.
On last issue with the idle. When I turn the car off and restart it after any period of time the idle decreases about 100 rpms. So after restart its idling around 550. running rougher too. A couple of blips on the throttle doesn't cure it. But it seems after about 3-4 minutes of running it goes away. The car is also running hotter than "normal" when idling for about 15 minutes or so. So when I took it out it was on the hot side. Only took about of minute of driving and the temp was down to more of a normal range. Maybe some sort of heat soak thing going on with my idle issues?
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Have you tied to adjust the idle mixture with the vac. gauge & set it to highest vac.?
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Yes, I have tried to use the vac gage while adjusting the mixture screws. When the idle increases I get the highest vac. but if I drop the idle down to a decent rpm (600-650) then the vac also drops to where it was before the mixture screw adjustment.
I'm going to try going back to man. vac for the dist advance and see if that pans out better.
thanks for your help!
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Yes & then when you drop the idle down to your 600-650 go back & reset the mixture screws again to that highest vac. I like your idea of trying the manifold vac. too just make sure when it's in gear if it's an auto, that the vac. doesn't drop below what the vac. can is rated for.
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I switched the vac advance over to manifold vac and plugged the ported vac source. Seems to run better. Idles at 625-650, 15-16 inches of vac. I've got the mixture screws out about 6 turns. If I turn them out any further the idle goes up and I have to adjust the throttle linkage screw out to slow the idle down. I can do this till the idle is too fast and the throttle linkage screw is not touching the throttle linkage. I've got it set right now that the throttle linkage screw is just cracking the primaries open and then adjusted the mixture screws in until the idle is where i want it.
Alls well with the idle until I turn it off sand restart. At restart it'll idle about 200 rpms slower. blipping the throttle a couple of times doesn't seem to help. Seems its more time related. about 2 minutes after restart it'll idle back where it should.
I'm wondering about the ignition/coil. I've got a Pertronix set-up with their coil. The last coil didn't last for more than 2-3 hours before it failed. If I feel this coil after I shout down the engine it feels almost like the oil inside is starting to boil again. I have a stock GM coil that I might try swapping. Only thing is Pertronix set-up for coil is supposed to be at 1.5 ohms this GM coil checks out at 1.4 and it states on the GM coil that its supposed to be use with a resistor in the ignition circuit. I thought the reason for the resistor was to prevent problems with points. I don't have the resistor and I don't have points. I don't think the GM coil should have any problems. Am I right on the GM coil?
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You should be fine with the GM coil. The electronic ignition is very happy with 12 to 14 volts. My experience with the resistor and electronic ignition is the resistor lowers voltage to a point where the ignition won't work.
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Update
I got the beast running pretty good.
The very slow idle after restart was cured by swapping out a new aftermarket coil with a new GM coil.
The inconsistent idling and idle speed issues were cured with a new fuel pump.
Now it idles at 625 without issues, has 16" of vac at idle. Starts at a touch of the key and best of all runs real well. Acceleration, throttle response all are very good.
Just goes to show that its not always the carb.
I want to thank all who help with advise and thank Cliff for making a great product. I'm so tired of buying new aftermarket stuff only to have problems with the stuff. But Cliff's stuff is the exception to the rule!! Thanks Again!!
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Good news!!!....Cliff