Cliff's Quadrajet Parts and Rebuild Kits
General Category => Quadrajet Carb Talk and Tips => Topic started by: Kavesh on January 27, 2021, 03:09:38 AM
-
Hi
I am trying to resolve a hesitation on take off on my quadrajet 7029282 which is on my Holden 308 stock standard engine. Motor has been recently rebuilt with 30 over pistons.
I rebuilt the carb in 2018 or 2019 with Cliffs rebuild kit with a new plastic pull off.
It has always had the hesitation but due to engine issues which was only now sorted I have not tried to fix the hesitation.
The internal parts on my quadrajet are 71 jets, 45B primary rods, AN secondary rods on a B hanger. (Do the hangers make a difference). Float is set at 10mm measured from the toe end of float.
Is this combination good for this engine. I am looking for good driveability and economy.
When cruising at 100-120km/h the motor is running really well.
I would love to get rid of the hesitation on take off. I really have to feather the accelerator to be able to get away from stand still.
I would appreciate any advice on this
-
Light throttle hesitation is usually too lean right off idle. I see this a lot building carbs here as nearly every one has the power piston hanger arms bent so the metering rods are not correctly located in the jets.
It can also be caused by the timing not advancing or not enough or too much of it.
Are you using vacuum advance? If so how much and ported or manifold vacuum source?....
-
I am using a vacuum advance and my source is manifold
When you say lean condition, meaning that my jets and rods on the primary side may be incorrect, as in the 71 jets and 45B rods? If so where I am located its not easy to find replacement parts and right now shipping small parts from USA is just not economical.
I can also confirm that the power piston arms are not bent and the rods are indeed in the jets.
What I have noticed is that I am not getting a good squirt from the accelerator pump. My pump is good and all openings are clear. When I disconnected the accelerator pump linkage from the primary shaft, and activate the pump with my hand, I can see really strong squirts on both sides. But with the linkage back on, the squirt is rather weak. Would this have anything to do with the hesitation I am experiencing?
-
Are you setting the idle mixture screws at idle in gear (A/T) for highest rpm/vacuum?
Can you have engine run worse with screws turned out from best setting?
If not, you may have to open idle fuel tubes and idle down channels some, ususally 2-5 thousands of an inch at both locations, start small.
-
Hi
Yes I have set the idle mix screws with the transmission in drive.
My understanding and I may be completely wrong here is that the mix screws does not affect off idle take off, the accelerator pump and jet and rod combination comes into play.
I would not be comfortable to make changes to the idle tubes.
This carb is the original carb from factory so in theory should not require any modifications, unless i am missing something?
-
Today the fuels contains less energy and yesterdays calibration can not deliver proper amounts of combustible air/fuel mixture, especially from the idle/off-idle circuit.
The accelerating pump supplies extra fuel when throttle blades opens rapidly, as in WOT from standing still, and the same goes for the main fuel/air supply.
For normal take-off, the idle/off-idle/low speed circuit delivers most of the needed air/fuel mixture.
And since the todays fuels are "leaner" than fuel was when our carburetored vehicles were new this circuit needs some help.
-
Thanks for the replies Kenth, much appreciated and understand that factory settings may not necessarily work with current fuels today.
I will try and do a bit more research into the idle off idle system before attempting any mods.
Would you be able to confirm whether my jet/rods combo is decent for my newly rebuilt 5.0 V8 Holden 308 stock motor.
My primary jets are 71 and rods are 45B
-
Primary jets #71 (.070"-.072") and rods 45B is not uncommon to see in units with .050" main airbleeds in air horn and float bowl.
Also,remember that the engine gets most, if not all, of the fuel / air mixture from the idle / low speed circuit at lower speeds and that it is involved in higher speeds, albeit to a lesser extent, at higher speeds, as the main circuit takes over to an increasing degree.
-
Thanks again.
Perhaps a silly question, but how on earth would i determine the main air bleed sizes or would they be a specific size based on carb numbers?
I would not have tools or access to tools to measure these air bleeds
-
If you can´t find a pin gage set, some drill bits might help.
1.1811mm .0465" #56
1.2mm .0472"
1.1906mm .046875"
1.25mm .0492"
1.3mm .0512"
1.3208mm .052" #55
Red lines marks the brass insert lower main air bleeds and yellow lines marks the upper main air bleeds in air horn.
-
Thank you
-
Just a quick update, the carb no longer has the hesitation on take off, so that is good.
New problem though, after assembling and starting up, she was idling smooth and strong with the idle screw just touching the primary stop. (not sure what its called)
After about a mile of driving I stopped at a traffic light and the idle was really bad the motor was very rough and shaky. Once above idle the carb performed beautifully.
I suspect there is some dirt in the idle circuit that may have dislodged and caused a blockage.
I don't think its dirt from my tank or lines as I have a nice big fuel filter in line before the fuel pump and its clean.
-
I have pulled the carb apart again and there was no dirt inside. It was clean.
In any event I went through and cleaned again just in case a passage was blocked. This time I even removed the idle tubes and they were clean. I also pushed wire through all the opening.
Sadly though I am still with this terrible idle. When I start up it is fine and as soon as the motor starts to warm up, and you go around the block the poor very rough idle returns. I can confirm there are no vacuum leaks.
This problem began when I swapped out the float bowl as I was not getting a good squirt from the previous bowl which seems to have improved with the bowl in question now, the hesitation is no longer present.
I am wondering whether there may be an issue with the float bowl. I was told by a buddy that perhaps there is fuel leaking internally on the idle circuit.
Please help me diagnose this. I have opened the carb so many times now, the airhorn gasket is looking a little tired now :(
-
btw my carb number is 7029282 which is an Australian Holden 308 V8 engine carb.
-
How far out are the idle mixture screws for best vacuum/rpm?
Can you have the engine run worse with screws further out from best lean idle?
How much vacuum in intake at idle in neutral and in gear (A/T)?
What rpms in neutral and in gear (A/T)?
All of above at normal operating engine temperature.
-
You mentioned swapping out the main casting.
Did you verify that ALL of the items were the same as the first one?
Lower Idle Airbleed?
Upper Idle Airbleed (if present above the DCR's)?
DCR the same size?
Idle tubes the same size?
Once fully warmed up if you tip the choke flap in or place your hand over it does the engine speed up and smooth out?....
-
Hi Cliff, the float bowls are meant to be to identical. The only exception is that one was made by carter 29282 and the other Rochester. 7009282.
I did not verify anything I guess. I used all the internal parts from the other other float bowl. with the exception of the idle tubes. Are the idle tubes not the same on these units?
I am not sure what the DCR's are, sorry.
When I placed my hand over the carb when it was idling badly it made no difference to the idle, however now that I have swapped over the float bowl, when covering the primary side the motor want to die.
-
Hi Kenth
So the mix screws were out 2 and a half turns on both and I tried opening them further but it made no difference at all.
I have not tried to attach the vacuum gauge recently as it seems I am chasing my tail!, yes it is an automatic.
I cannot advise on rpm either as my truck does not have a tach.
In any event I have not swapped out the float bowl, I am back with the Carter built unit. Base plate and airhorn are reused. All internals were also swapped except for the idle tubes. (How does one tell the size of the idle tubes?)
I have the idle mix screws set at 1 and 3/4 turns out, and the motor is idling fine, could not go for a drive as yet. I suspect the off idle hesitation may be back but can only confirm when driving. When I bump the accelerator initially it does not respond immediately on the second attempt it increases rpm faster. What causes this issue, no blockages found in any passages.
As my airhorn gasket was looking a little damaged, I decided to use 2 gaskets, one slightly thicker one and the original thinner one that was on the carb. Will this be fine or should I go back to a single gasket.
-
Poor response when you push the throttle on the first attempt then improved on the second could be several things. Accl pump check ball leaking or the engine is "loading up" some at idle and needs cleared out.
I would NOT double up the gaskets or use one that wasn't in good shape.
I have .015" and .030" thicker main body to airhorn gaskets for the early units. A poor fit between the main casting and airhorn could be part of the issues you are seeing.
I suspect the carb is lean on the idle system contributing to the off idle stumble.
Idle tubes are measured using precision drill bits. A set with #61-80 will have the needed sizes......
-
Thanks Cliff, I will go back to the single gasket on the airhorn. Will use the thicker of the 2.
I wish I was closer to the USA to pick up a new kit from you, but right now cost of shipping to South Africa is ridiculously expensive. It is sad that my current kit from you which has not seen much miles is getting ruined due to trying to fix issues as explained on here.
Without the precision tools would you say it would be a good idea to swap in the idle tubes between the 2 float bowl casting? Perhaps this will give me the response needed. (I am no carb expert so correct me if my logic is not right).
-
Swapping parts around isn't the answer without knowing what sizes the sizes of the other items involved.
A Carter unit sporting the same part number may not be set up exactly the same as a Rochester.
Instead of guessing I measure everything, upper IAB's, lower IAB's, DCR's, bypass air, mixture screw hole size, transfer slot length and location, etc before making any changes. With the correct information we can make small changes to improve fuel delivery in the areas where the engine is wanting it.
There are ways other ways we can make educated changes. If you suspect the carb is a tad lean at light part throttle causing the hesitation right off idle you can temporarily tip the choke flap in slightly to richen things up then lock it there for a quick test drive, for example.
My "tip-in" test works well to tell us if the carb is lean at part throttle. Set the fast idle around 2000rpm's then gently "tip-in" the choke flap and see if the engine speeds up? If it speeds up more than about 200 rpms then the jet/rod relationship is pretty lean for what you are doing and going to a .001-.002" smaller primary metering rod will put some fuel in that range.
If the problem is at a very low throttle opening transitioning from idle to the main system we can put more fuel there with a slightly larger idle tube and/or opening up the DCR's slightly.
None of these changes are irreversible, as we can also go back to the stock set-up and even the other direction if/as needed........Cliff
-
Thanks Cliff, really appreciate the advice.
I understand that you as a pro builder will make sure that the internals are what they need to be for the client.
In my novice rebuilding limited skill and tools, I am able to do the basic stuff. Understanding exactly how everything works is also not easy.
I do take your advice though and have removed the additional airhorn gasket. I have also read somewhere that raising the float level will richen the mix, which may help my off idle hesitation.
Currently I have my float set at 11mm or 0.43 inches. This level as far as I know is the factory setting.
Is there a direct relationship with float level and rich/lean at idle and off idle.
-
Are you using an OEM float or brass?
That float setting is really low for one of those carburetors.
I'd use the correct OEM nitrophyl float set at 1/4" (.250") and see if that helps some.....
-
I am using the OEM float.
I have raised the float level as suggested and removed the clip from the needle and seat as it was giving me some trouble.
It would appear that I am running too lean at idle. When I close the primary flap slightly and cover my palm over the primary side the idle speed picks up and the idle smooths out.
As I do not have smaller primary rods, but have 76 jets, I am going to try that today. I am assuming that the larger jets will at least confirm that I have a lean issue at idle. Yes I also realise that the 76 jets in all likelihood will be too big for my application but its will at least narrow down my problem and then I can look for suitable rods for my 71 jets.
-
Changing main jets will do nothing for idle leanness.
As we´ve discussed earlier, the idle circuit is a standalone circuit and it supplies engine with A/F mixture at idle speed/low speed.
You will have to look into idle tube restrictions (idle jets), upper idle air bleeds, downchannel restrictions (DCR), lower idle airbleeds, off-idle slots, idle mixture discharge holes (at idle mixture needles) and idle bypass air for suitable sizes for what you are doing.
-
I've seen superficial improvement to idle fuel delivery installing HUGE jets simply because all the to the idle system goes past the jets/metering rods first and the PP is in the down position.
Even with that said Kenth is correct you are making changes to the wrong area.
If you have the engine fully heat soaked, timing is correct, and idle speed is where it should be, adjust the mixture screws for best idle quality at the leanest settings. This is done by backing them out pretty far then turning them in slowly one at a time until you notice a speed change or slight reduction in vacuum or engine RPM's. Then back them up for highest vacuum and idle speed which should be about 1/2 to 1 turn from the "lean tip-in point".
That will be a good place to be for idle fuel. Once you've established best idle quality repeat your "hand over the choke" or tip in the choke flap and see if things improve. If so you need more idle fuel to the mixture screws to correct/cure your issues, not larger jet sizes.......Cliff
-
This is a HUGE learning experience for me.
As you quite rightly pointed out the bigger jets will do nothing for the idle, and I can confirm that, after installing the 76 jets.
I have 2 other scrap QJ and had a look at those primary rods and they are all 45B's like the ones on my motor. These carbs are the same part number 7029282 as what came from factory on the Holden 308 engine. Perhaps todays fuel has a bearing on why some of the internals are no longer suited and need other part sizes.
I will persevere with your assistance to get this carb sorted.
-
Just an update.
A buddy of mine has lent me his spare QJ, 7026202 to test. This carb is missing the choke pulloff and auto choke assembly.
The good news is that it runs good on my engine. I took her for a short ride yesterday and she went well.
I was told that it has 76 jets and 47 primary rods. Not sure about anything else.
What I found interesting is that on face value the one difference i spotted is that on the airhorn, the upper air bleeds on mine does not have any brass inserts whereas the carb from my mate has brass inserts.
Are these different model carbs designed like this or have they been modified at some point.
-
His carb has been modified. May have been thru one of the commercial rebuilders at some point.
Originally those had 71 main jets and 44 or 45B rods from what I can remembers, and small main airbleeds in both locations.
Your carb is a much better unit all the way around, you just need to get some more fuel to the idle/off idle and it will be fine. Those early units had a plunger/bypass type fuel inlet arrangement and are HOPELESS even with a conversion in them. They also had a weighted secondary air shaft system which gave them a bad reputation for "bogging" when you go quickly to the secondaries.
Every single plug in them typically leaks when they come in here for rebuilding, giving the entire line of Q-jets another undeserved bad reputation for leaking bottom plugs........Cliff
-
Thanks for that information Cliff.
O am planning on sending my carb to my mate for him to try and resolve as I seem to have hit a brick wall.
He has gone through several QJ, in the last few years and seem to have a good understanding of their design and workings. He seem to have resolved whatever issues they may have had.
I am hoping that he will find the problem with mine and fix it for me.
The other noticeable difference i found is how responsive the mix screws are on his carb compared to mine. While mine does respond , it usually takes more than half a turn to notice a difference. Whereas on his carb you can hear and see a change in engine speed with 1/4 turn.
-
You simply need more fuel to the idle system. This will also put more fuel to the off idle transfer slots and cure your issues.
Pretty sure that was mentioned earlier at least once.
It could be as simple as effectively cleaning the idle tubes as they tend to get smaller over the years as "varnish" builds up in them with many drying up cycles.
Here I remove them from the main casting and manually clean them with precision drill bits. For this new fuel I open them up in almost all cases and to date have never had a single complaint from the end user and I'm well over 15,000 units at this point........Cliff
-
Yes you are quite right it has been mentioned before about fuel delivery at idle.
I have removed the idle tubes and used wire to ensure the tubes are clear. I do not have the precision drill bits to be precise on this.
I must say though that the idle tubes were not blocked nor was there any muck in the main body. This is what has me stumped.
I am hoping a fresh set of eyes in my buddy would see what the issue is and sort it for me. Perhaps I have been looking at it for too long now.
I will post an update in due course.
-
There is no way around enlarging the idle tubes and idle down channels.
Now is the time to get a set of precision drill bits.
-
What will the impact of the plastic retainer for the power piston be when its installed upside down.
My mate said that he noticed this installed incorrectly. See pic attached.
I have had this in the carb for probably 2 years of longer with no known problems, until the carb issues I am experiencing now.
Will the power piston collar have any effect on the carb when installed upside down?
Thanks
-
No real ill effects. Obviously the power piston will not rise the full distance with the retainer upside down but the taper on rod should still leave the jet enough at WOT or heavy load manouvers.
And, this has NO effect on idle and off-idle issues.
-
Thanks Kenth. My mate will have a good look this weekend and hopefully find something else.
He mentioned that he believed the play on the primary shaft was alot. As the carb worked fine before I did not pay too much attention to the shaft.
My mate offered his theory here.....prior to motor being overhauled, vacuum may have been low which was not noticeable at the shaft. My motor is now rebuilt and vacuum should be higher which is now showing itself at the shaft and causing an idle issue. His logic makes sense but my vacuum is pretty low at 13 inches steady at idle. Perhaps i need a bit more timing to increase vacuum.
-
You mentioned that the engine was "rebuilt".
13" vacuum is pretty low for a "stock" rebuild using a stock camshaft. Did you use something other than a stock cam during the rebuild?
Another BIG mistake folks make when "rebuilding" engines is not paying attention to quench.
Many oversize aftermarket pistons are shorter than stock ones for pin height placing them deeper in the bores at TDC. This LOWERS the compression ratio when it should actually raise it with the larger CID.
Most head gaskets found in "builder" gasket sets and THICKER than the stock ones which raises the cylinder heads off the engine and LOWERS the compression ratio.
Most engine "builders" either don't know these things or don't address them during the rebuild, so the engines compression ratio is typically lower than it was before the rebuild.
It's also common to replace the camshaft with an aftermarket cam of some sort instead of using a cam with stock specs. If a larger cam (more duration) is used this LOWERS dynamic compression, which hurts idle vacuum, idle quality and throttle response right off idle, etc.
Other mistakes I see with engine builds are not degreeing the camshaft and using "double roller" timing sets in them. Most of the roller sets being sold are JUNK!!! They are "weak" compared to the factory Morse chain set-ups, they do NOT offer constant tooth contact (smoother), not as accurate and the chains can stretch out very quickly.
Adding a high pressure and/or high volume oil pump is another BAD decision I see made with a lot of these engines. Stock oil pumps are more than adequate for all stock and most performance engine builds. Larger pumps rob power and put a LOT more load on the oil pump drive and distributor/cam gear, often wearing them out quickly.
I could add at least a half dozen more items to this list but I'll stop here.
Just throwing a few things out there that may be contributing to your problems........Cliff
-
Thanks for the indepth reply Cliff.
Let me update on my carb first. My mate said that when he stripped it down he noticed that the seat for the needle and seat was not screwed in tight. With me having opened it up so many times i did not remove the seat each time so maybe this is my own doing. Perhaps the reason for the idle issues!
What impact does a not fully tightened needle and seat have on the carb? Rookie mistake I have made.
The carb was assembled by my mate and it is running fine on his test engine which is the same engine I have on my truck. I should have it back in a couple of weeks.
With regards to the low vacuum, I also was not happy with it.
The cam as best I know shoudl be a stock aftermarket replacement.
With the Holden 308 motor the replacement pistons are Chev 327 pistons. All rebuilders seem to use these as the Holden brands are just too expensive, if you can find stock.
My head gaskets are Felpro which as far as I understand are a little thicker.
My timing chain is double row like the original
Also using a standard oil pump.
Once I get my carb back I will try to determine why my vacuum is on the low side.
-
No direct experience with the Holden engines.
A 327 Chevy, or even a 350 would have came from the factory with a camshaft that made at least 18-21" vacuum at idle speed with very little timing in it.
They NEVER used "double roller" timing sets in any of those engines, they were all the Morse type.
Contrary to popular belief the vast majority of the double roller timing sets being sold are NOT an "upgrade" over a stock type set. Most have cheap chains (poorly made or not "true roller") and cast iron sprockets. The "high end" varieties use billet sprockets and a real heavy duty true roller chain, but even those aren't nearly as strong as a factory style chain and probably why the factory used that variety instead.
Morse chains only got a bad reputation because early on they used a nylon coated top sprocket to minimize noise and absorb harmonics between the crank and cam. Those were actually excellent sets but over time heating/cooling cycles caused the plastic to crack and teeth would start falling off of them and eventually fail.
In my own engines here I will only use factory wide link type (Morse) timing sets and have had zero issues with any of them dating back nearly 50 years.
I tried a "high end" Rollmaster timing set once on my first 455 built in 1999 and it failed after 4 years of pretty hard use. I loved the ease of moving the cam around (9 keyway variety) and thought it would be a nice set-up for my engine back then. Sadly the chain got so loose it started "slapping" and retarded the cam so far the car slowed WAY down at the track.
Anyhow, a loose fuel inlet seat if leaking slowly will not provide full control of the fuel level in the carb and issues with fuel delivery as the fuel level has a direct impact on metering. I see quite a few leaking fuel inlet seats due to damage to the gasket surface. When the leak is really slow they car typically drives fine, but may "load up" when you stop if/when the leak is faster than the fuel the engine is consuming at idle.
It may also cause flooding after shut-down if there is still fuel pressure in the line between the pump and carb. For sure it's often difficult to diagnose but more common that folks think........Cliff
-
Hello
Here is a further development on my carb issue. As mentioned before my buddy has leant me his spare quadrajet to use on my truck. For a few weeks now it has been working perfectly.
Yesterday I wanted to go for a drive and noticed that it was not idling like it should. The truck was last used a week ago. It is displaying the same issue I have had with my carb with the erratic idle.
Thinking that some dirt has got in I removed the airhorn and could not find any dirt inside the carb.
Nevertheless I used wire to make sure all the orifices are clear and they were.
Closing the primary flaps did smooth out the idle and the RPM increased. I am really confused guys, am I chasing a carb issue when in fact my issue may be elsewhere, or is this a lack a fuel on the idle circuit. If it is a lack of fuel why would it be fine for weeks and now display these idling issues.
Just to confirm I have not interfered with anything on the motor since last operated.
I will try and upload a video
-
Here are the videos on youtube
https://www.youtube.com/watch?v=WSnqfFfRq9U
https://www.youtube.com/watch?v=Pl9vtBegGy4
https://www.youtube.com/watch?v=_4hrdZREmLU
-
Sounds like you´ll need to adjust the valves.
What does an intake vacuum meter show?
-
The Holden 308 does not have adjustable valves like the Chevy motors.
I did not put the vacuum gauge in yesterday but will do.
-
I checked a couple of things today.
As I am using an HEI, i tested the voltage to the wire going to the BAT terminal on the dizzy with ignition on, read 11.93volts. Is this a real problem as it should be 12v?
Started up the motor and she struggled to idle. At higher revs there were no issues. I let the RPM down gradually and down to idle and when it wanted to die I used my fingernail to push down the accelerator pump which gave it a shot of fuel, this kept the motor running, and then another shot of fuel when it wanted to die to help it run.
Will the above test be sufficient evidence that the problem is indeed the carb and on the idle circuit?
-
Take a measurement over the battery at idle, should read 13.5-14.5 volts.
This is what you should read at the HEI.
I have forgot how many "carb issues" i have cured for folks by feeding the HEI with correct voltage.
The HEI needs a dedicated feed wire, not the wires aimed for the points distributor which contains a resistor cable reducing volts an amps for the points to live.
You may use the points wires to control a relay from which you feed the HEI.
Been there done that a couple of decades ago, now i´m running the factory points ignition system again since i don´t care for the looks of the big ugly HEI and i don´t mind tinkering with points, checking/setting dwell once a year and replace the points every 10:th year or so.
JMHO
-
The voltage at the battery while idling at 13.9v, confirming a good charge from the alternator.
I have bypassed the resistor wire when I installed the HEI a few years ago.
I am assuming you mean with the engine running to get the same voltage at the BAT terminal as recorded across the battery?
I need to figure out a safe way to do this test.
I am hoping to borrow a fuel pressure regulator to test whether my fuel pressure is good enough for the quadrajet. If I recall between 5-7psi would be ok.
I will report back soon.
-
you want to see battery voltage @ the red 12v plug at the distributor. ideally the same as what you are reading at the BAT terminal. ie: 13.8Vdc,not 13.5 or 12.9,etc. if readings are identical this means there is no voltage drop which is what you want. if readings are not the same this means you could have a bad connection, undersized wire, resistor wire, bad distribution, etc
-
Hey guys, just an update
I found a possible issue on the intake. When the motor was apart for overhaul, I decided it was a good time to relocate the carb return spring to the rear of the intake. Mine originally was located at the front of the intake. During the drilling and tapping I made a hole through the intake. When I assembled the motor I used thread tape on the bolt into the hole to seal.
I removed the bolt and noticed the area slightly oily, perhaps a small vacuum leak here. I put thread tape again and the erratic idle seemed to have gone away.
I have now used RTV on the bolt threads to try make a better seal after removing the thread tape.
I still have both carbs and will test over the weekend to see whether there is a marked improvement.
Any better suggestions for a better seal on the bolt hole?
-
Use a stud instead of a bolt and coat it with Marine Tex or a very high grade epoxy......
-
Thanks Cliff, thats a brilliant idea :)
-
Just to close this off now, I have used a bolt as Cliff suggested with some high grade epoxy.
So far so good 8)
Thank you to everyone that contributed to this thread. I would not have been able to do it without the advise given here.