New Qjet carb - Starts, then dies

[1968_K20_4x4]

Hello Everyone!

I purchased a rebuilt (Autoline from Napa) Quadrajetet carb for my 1972 Chevy K20. I installed it with an aftermarket electric choke kit from Quadrajetparts.com, however the truck does not start like it should. I gently press the pedal to the floor once to set the choke, it will fire up, run for 2 seconds, then die. I wait a few seconds, press the pedal to the floor again and re-start. The truck will then start and run fine.

I have tried a few tricks- half a pump then crank to start, two pumps then crank to start, adjusted the choke rich/lean, adjust idle set screw, hot or very cold day - the truck starts the same way every time. No matter what I do the truck starts then dies after a couple seconds.

The choke pull-off appears to be working properly as it pulls the choke blade open slightly right away.

When its warmed up the truck always starts right away and runs fine with no issues, although it does seem very easy to flood when warm and once flooded will not start even if you hold the pedal to the floor.

I am wondering if it is a fuel delivery problem... I am running a lower pressure fuel pump (4-6psi) with an inline fuel filter as well as the stock filter inside the carb... Maybe not enough fuel on start up???

I have not adjusted the Choke Pull-off or the high-idle.

I am new to carb adjustment/tuning so any insights as to what is going on here or ideas of what to check/adjust next would be greatly appreciated.

I have attached a couple crappy pics - I can take better ones of the carb set up later but for now this is all I have (BTW my motor is a marine 307 if youre wondering..lol)

[RustyPile]

Originally Posted by 1968_K20_4x4

Hello Everyone!



The choke pull-off appears to be working properly as it pulls the choke blade open slightly right away.



I have not adjusted the Choke Pull-off or the high-idle.

"Slightly open" is not a proper adjustment. If you live in a cold climate, The cold engine choke and fast idle settings need to be "tighter" than what's needed in warmer climates.

Adjust the choke pull to open the choke about 1/8" to 3/16".. Do this with the engine cold, not running. Choke closed and using a hand-held vacuum pump, pull the choke open. Bend the linkage to achieve this setting.. Screw in the fast idle adjustment screw a few turns. Bump the throttle to set the fast idle screw on the top "notch" of the fast idle cam. Start the engine and immediately set the fast idle RPM around 1200 - 1300 Rpm.

During my days as a driveability tech, during initial start-up, I've had to set the fast idle at 1800-1900 RPM to keep an exceedingly "cold natured" engine running in the dead of winter.. After running at that speed for 15 - 20 seconds, a light tap on the throttle will bring the fast idle cam down a notch or 2 and the still cold engine will run about 850-1000 RPM and do just fine. Such drastic and aggressive settings aren't required in our most southern states.

All this assumes you have already set the proper ignition timing.

[Rich72C10]

Originally Posted by RustyPile

...

Adjust the choke pull to open the choke about 1/8" to 3/16".. Do this with the engine cold, not running. Choke closed and using a hand-held vacuum pump, pull the choke open. Bend the linkage to achieve this setting.. Screw in the fast idle adjustment screw a few turns. Bump the throttle to set the fast idle screw on the top "notch" of the fast idle cam. Start the engine and immediately set the fast idle RPM around 1200 - 1300 Rpm.

....

I am not sure I have seen this adjustment described this way (or I just didn't understand it). It just happens to be GREAT weather to test this and set things right.

To make sure I have this right, with Engine Cold / Don't Start it:
1. Insure Choke Plate is closed (top of Carb) - Completely at this point?
2. Remove Vacuum line between Choke Pull and Carb (the PITA little one - front/passenger side that looks like it is shaped like an elbow pasta).
3. Hook up your vacuum pump to fully engage vacuum Choke Pull.
4. Insure choke plate is 1/8" ~ 3/16" opened by bending the linkage on the Choke Pull?

I am okay on how to adjust the Fast Idle levels/stages and have adjusted them by forcing the low/high fast idle stages while running.

[RustyPile]

Originally Posted by Rich72C10

I am not sure I have seen this adjustment described this way (or I just didn't understand it). It just happens to be GREAT weather to test this and set things right.

To make sure I have this right, with Engine Cold / Don't Start it:
1. Insure Choke Plate is closed (top of Carb) - Completely at this point?
2. Remove Vacuum line between Choke Pull and Carb (the PITA little one - front/passenger side that looks like it is shaped like an elbow pasta).
3. Hook up your vacuum pump to fully engage vacuum Choke Pull.
4. Insure choke plate is 1/8" ~ 3/16" opened by bending the linkage on the Choke Pull?

I am okay on how to adjust the Fast Idle levels/stages and have adjusted them by forcing the low/high fast idle stages while running.

You got it right!! You won't find these exact settings "in the book".. But it's not unorthodox either.. I don't want to come across as bragging but I worked as a driveability mechanic back in the '80s - '90s.. I had some real Lulus thrown at me.. I'm not a proponent of throwing away the instruction book, but as I stated: extreme cases call for extreme procedures.

If these carburetors weren't meant to be adjustable, there wouldn't be so many adjustable features on them.. Check your timing and all the other basics -- fuel pump condition, quality of gas, thermic operation, heat riser, etc. All these things aid, or at least take part in the warm-up process. If that doesn't cure the problem, THEN start looking "outside the box".. In climates like Arizona has, that 1/8" - 3/16" is way to "tight".. A quarter inch works much better. and also a looser choke bi-metal setting will allow a faster choke opening.. It's all climate related. The settings are different, but the procedure is the same.

I've rebuilt and replaced so many Q-jets, I've lost count. That cold start choke "tune-up" is a procedure I developed a long time ago.. It's geared more toward climatic conditions than any "generic" instruction sheet procedure.

My old C/10 doesn't have anything (fuel delivery system) on it now that came from the factory. It has a warmed over 454 with a Holly 3310-3 sitting on top. Sometimes it sits for weeks without being started.. Without going into a long detailed description of what I did to make all the parts play well together, the engine busts off every time without fail.. No "re-starts, stumbling, nothing.. Now East Texas doesn't have anywhere the climatic conditions like Canada.. We have sub-freezing winters, only a few days at a time.. Blazing 3 digit summers for weeks at a time.. Through all that, that old BBC just chugs right along.. It took a little work on my part, but it does work now.

[Rich72C10]

Originally Posted by RustyPile

You got it right!! You won't find these exact settings "in the book".. But it's not unorthodox either.. I don't want to come across as bragging but I worked as a driveability mechanic back in the '80s - '90s.. I had some real Lulus thrown at me.. I'm not a proponent of throwing away the instruction book, but as I stated: extreme cases call for extreme procedures.

If these carburetors weren't meant to be adjustable, there wouldn't be so many adjustable features on them.. Check your timing and all the other basics -- fuel pump condition, quality of gas, thermic operation, heat riser, etc. All these things aid, or at least take part in the warm-up process. If that doesn't cure the problem, THEN start looking "outside the box".. In climates like Arizona has, that 1/8" - 3/16" is way to "tight".. A quarter inch works much better. and also a looser choke bi-metal setting will allow a faster choke opening.. It's all climate related. The settings are different, but the procedure is the same.

I've rebuilt and replaced so many Q-jets, I've lost count. That cold start choke "tune-up" is a procedure I developed a long time ago.. It's geared more toward climatic conditions than any "generic" instruction sheet procedure.

My old C/10 doesn't have anything (fuel delivery system) on it now that came from the factory. It has a warmed over 454 with a Holly 3310-3 sitting on top. Sometimes it sits for weeks without being started.. Without going into a long detailed description of what I did to make all the parts play well together, the engine busts off every time without fail.. No "re-starts, stumbling, nothing.. Now East Texas doesn't have anywhere the climatic conditions like Canada.. We have sub-freezing winters, only a few days at a time.. Blazing 3 digit summers for weeks at a time.. Through all that, that old BBC just chugs right along.. It took a little work on my part, but it does work now.

Like to follow up, thank you for the tips on using a vacuum pump on the choke pull. This really helps to see what the choke plate is doing between choke off, then at fast idle stages with and with out the choke pull in action. I kept just trying to adjust the choke plate without taking in consideration of when the engine applied vacuum to the choke pull.

Now I have super happy starting, though it hasn't gotten below freezing again since I started the proper adjustments.

again, thank you RustyPile.

[RustyPile]

Originally Posted by Rich72C10

Like to follow up, thank you for the tips on using a vacuum pump on the choke pull. This really helps to see what the choke plate is doing between choke off, then at fast idle stages with and with out the choke pull in action. I kept just trying to adjust the choke plate without taking in consideration of when the engine applied vacuum to the choke pull.

Now I have super happy starting, though it hasn't gotten below freezing again since I started the proper adjustments.

again, thank you RustyPile.

You're welcome, Richard.... Glad I could help.. The important thing is you learned a little bit of how the cold start enrichment system works on a Q-Jet.

[dz1087]

Originally Posted by RustyPile

.....and also a looser choke bi-metal setting will allow a faster choke opening..

How do you loosen this thing up? Mine keeps going back in to high idle after I drop it down in to the lower idle setting while beginning my drive. Very annoying to have the thing keep dropping back in to high idle while driving for the first 10 minutes or so. Only does it when its 60 or less outside.

[Caddylackn]

There really is two settings for the automatic choke. A winter setting and a summer setting. The predecessor to the quadrajet (4 jet) actually had these two different settings labeled on the automatic choke housing. Rotating the housing to the winter setting increased the rotating spring tension and gave it more choke for winter. In the summer this will leave the choke on too long, so set it back to summer setting.

If I was the OP, I would put a mark on the housing for the winter setting, and when its tuned for summer I would put another mark.

[RustyPile]

Originally Posted by dz1087

How do you loosen this thing up? Mine keeps going back in to high idle after I drop it down in to the lower idle setting while beginning my drive. Very annoying to have the thing keep dropping back in to high idle while driving for the first 10 minutes or so. Only does it when its 60 or less outside.

I don't know your level of knowledge about automatic chokes, so I'll start with the very basics of how it works. The choke mechanism is located on the passenger side of the carburetor. There is a round black plastic housing that covers the bi-metal spring that controls the choke blade located at the top of the carburetor. This cover is held in place by 3 small screws located around the perimeter of that cover. The spring is temperature sensitive. When cold, it winds up (tightens) and pulls the choke blade closed. When heat is applied (either by electric current or from heated air) it unwinds (loosens) and the choke opens up gradually.

The spring tension is adjustable. In your case, the spring needs to have a looser setting.. The setting is done with absolutely no heat in the engine. With the engine stone cold, having sat overnight, loosen those 3 retaining screws. It's not necessary to remove them, just loosen them a turn or two. Prop the throttle open to release tension on the fast idle mechanism. Rotate the black cover in the direction that causes the choke blade to open. Rotate it until the choke is fully open. Rotate the cover back the other direction until the choke fully closes. Rotate the cover another 1/8". Hold it in position and tighten the screws. If all other adjustments are correct, the choke should be fully open after about 3 - 5 minutes of run time, depending on outside air temperature. If the choke opens too fast, turn the cover another 1/8". After initial adjustment of the spring, any additional adjustments should be very small amounts.

For fast idle speed adjustments, refer to my previous posts on this thread for those settings.

[RustyPile]

Originally Posted by RustyPile

"Slightly open" is not a proper adjustment. If you live in a cold climate, The cold engine choke and fast idle settings need to be "tighter" than what's needed in warmer climates.

Adjust the choke pull to open the choke about 1/8" to 3/16".. Do this with the engine cold, not running. Choke closed and using a hand-held vacuum pump, pull the choke open. Bend the linkage to achieve this setting.. Screw in the fast idle adjustment screw a few turns. Bump the throttle to set the fast idle screw on the top "notch" of the fast idle cam. Start the engine and immediately set the fast idle RPM around 1200 - 1300 Rpm.

During my days as a driveability tech, during initial start-up, I've had to set the fast idle at 1800-1900 RPM to keep an exceedingly "cold natured" engine running in the dead of winter.. After running at that speed for 15 - 20 seconds, a light tap on the throttle will bring the fast idle cam down a notch or 2 and the still cold engine will run about 850-1000 RPM and do just fine. Such drastic and aggressive settings aren't required in our most southern states.

All this assumes you have already set the proper ignition timing.

To make this clearer.. The settings I suggested are for the OP's cold Canadian weather. I assume he is having these issues now with sub-freezing temperatures and several inches of snow on the ground. For other people, the procedure is the same, but settings may vary, depending on the individual engine and the climate/altitude where it's being operated.

These days, the engine management computer can make allowances and adjustments so problems never arise.. 50 - 60 years ago, traveling on long trips were a hassle because the carburetor calibration needed changes so much with climate change.. I remember one of these trips our family took in a '61 Chevy.. Our home was on the gulf coast of Texas near its border with Louisiana. We went to Pikes peak and through Colorado. Those mountains gave that car fits.. That Chevy belched black smoke and stumbled along until we got back down to sea level altitudes.

[Steeveedee]

"California and Denver" jetting. Back in the '70s, I worked at a parts store for awhile. We sold "replacement" carburetors. No matter who walked through the door, a replacement Q-Jet was the same, 250 to 455 Cu In Pontiac, whatever. Same deal for Motorcraft and Holley. I bought one of those Q-Jets to put on my 327, but it needed work to make it right.

[RustyPile]

Originally Posted by Steeveedee

"California and Denver" jetting. Back in the '70s, I worked at a parts store for awhile. We sold "replacement" carburetors. No matter who walked through the door, a replacement Q-Jet was the same, 250 to 455 Cu In Pontiac, whatever. Same deal for Motorcraft and Holley. I bought one of those Q-Jets to put on my 327, but it needed work to make it right.

That's pretty much the way it was back in those days. As a driveability tech, it was my job to do that work. I'd do a replacement only if the original was beyond repair. Most of the time, I'd start the job by removing the jets and rods from the old carb and installing them in the new (remanufactured) one.. All other adjustments - secondary air valve, choke adjustments, idle mixture, etc was just based on my experience.

I started racing in 1969. I learned what makes a Q-Jet "tick" during my early racing days.. The class/combination I ran required a stock Q-Jet... It's amazing what can be done to those carburetors..

[1968_K20_4x4]

Originally Posted by RustyPile

"Slightly open" is not a proper adjustment. If you live in a cold climate, The cold engine choke and fast idle settings need to be "tighter" than what's needed in warmer climates.

Adjust the choke pull to open the choke about 1/8" to 3/16".. Do this with the engine cold, not running. Choke closed and using a hand-held vacuum pump, pull the choke open. Bend the linkage to achieve this setting.. Screw in the fast idle adjustment screw a few turns. Bump the throttle to set the fast idle screw on the top "notch" of the fast idle cam. Start the engine and immediately set the fast idle RPM around 1200 - 1300 Rpm.

During my days as a driveability tech, during initial start-up, I've had to set the fast idle at 1800-1900 RPM to keep an exceedingly "cold natured" engine running in the dead of winter.. After running at that speed for 15 - 20 seconds, a light tap on the throttle will bring the fast idle cam down a notch or 2 and the still cold engine will run about 850-1000 RPM and do just fine. Such drastic and aggressive settings aren't required in our most southern states.

All this assumes you have already set the proper ignition timing.

Many thanks to RustyPile!! You're a genius!

I finally got a chance to get out in the garage and start working on the truck again today. I did exactly as instructed, and my truck fired right up and ran beautifully! Never stalled or hesitated at all. Thank you so much for this info, you helped me get my truck up and running great again. One other thing that I checked was the torque on the carb mounting bolts and they were all a little bit loose.

Note to Richard- no worries at all I am glad that this thread also helped you get your truck running great as well.

Thanks to those who suggested a different choke setting for summer vs. winter, I will definitely keep that in mind and I may have to re-adjust come summer time. But I am very happy to know how to do that now!

Thanks again to everyone who replied to help me get this issue sorted out!

[1968_K20_4x4]

So in the summer, I will re-adjust my choke as needed.

When driving my truck around in the summer, will I also have to re-adjust the choke pull off? as in re-bend the linkage for summer operation? Or will the current setting be Ok for summer driving as well?

Thanks

[RustyPile]

Originally Posted by 1968_K20_4x4

So in the summer, I will re-adjust my choke as needed.

When driving my truck around in the summer, will I also have to re-adjust the choke pull off? as in re-bend the linkage for summer operation? Or will the current setting be Ok for summer driving as well?

Thanks

Thanks for the praise, but I assure you I'm no genius. Just well trained by GM's Houston, Tx training center and backed by YEARS of experience back in the day. As I've stated in other posts, I once did this on a daily basis for a living.

Now to answer your question on the choke pull. Once you have it adjusted you shouldn't have to adjust it for warmer weather. Some engines are more "cold natured" than others and may require a different setting on the choke spring for extremely cold temperatures vs. hot weather. The choke pull setting should work year 'round for you. I'd suggest you wait until summer (or warmer weather) shows up and see how the choke works for you. If the engine seems to run on the fast idle cam to long, mark the position of the choke housing and loosen those 3 screws. "Unwind" the choke spring. Do this in very small increments, about 1/8" at a time. I'm guessing you won't have to do any summer - winter changing.

[geezer#99]

Originally Posted by 1968_K20_4x4

So in the summer, I will re-adjust my choke as needed.

When driving my truck around in the summer, will I also have to re-adjust the choke pull off? as in re-bend the linkage for summer operation? Or will the current setting be Ok for summer driving as well?

Thanks

You’ll need to wait and see if you need to adjust again.
Problem is your season changes aren’t always consistent. The transition times from summer to fall and then winter and spring to summer will vary.
You just need to wait and see how your motor reacts.
I’ve found I needed a lot of patience to wait as long as possible before I changed
Settings.
I spent the first 55 years living in 40 below country. Mostly in Alberta where I’ve seen temperature swings of 40 below to zero and back to 40 below in but 6 hours.
My ultimate cure was using a manual choke on any carb. Always worked the same way year round.

[Rich72C10]

Originally Posted by 1968_K20_4x4

.... One other thing that I checked was the torque on the carb mounting bolts and they were all a little bit loose. ....

Word to the wise, don't torque and 100% don't over torque - the fellow that rebuilt my carb (Cliff Ruggles of Cliffs High Performance) said this:

Originally Posted by Cliff Ruggles

Don’t torque the bolts just snug them down, torquing them will warp the carb and can cause the secondaries to stick open slightly.

I then pointed out the GM manual about torque and he followed up again

Originally Posted by Cliff Ruggles

NO, do not torque those bolts or you will ruin the carburetor.......

So, ya I don't torque as I don't want Cliff to pop one on up side my head. LOL

[1968_K20_4x4]

Originally Posted by Rich72C10

Word to the wise, don't torque and 100% don't over torque - the fellow that rebuilt my carb (Cliff Ruggles of Cliffs High Performance) said this:


I then pointed out the GM manual about torque and he followed up again


So, ya I don't torque as I don't want Cliff to pop one on up side my head. LOL

Thanks for the heads up on this- to clarify I didn't actually torque the bolts down like the manual says as I don't have a torque wrench that goes down that low. I just snugged them up with my ratchet- I tightened them up but hopefully I didn't go too tight!

[1968_K20_4x4]

Thanks guys for the advice about adjusting the choke. I will see how the truck runs in the summer and reference this thread again if I do need to make some adjustments. Most of the driving I will do will be in the summer, but I want the truck to start reliably and consistently in cold weather as well for the few occasions where I do want to use it on freezing cold days the fall.

Thanks again for all the help and knowledge! I couldn't keep these old trucks running without all your help!

[Caddylackn]

You are not going to want to hear this: but putting on a rebuilt generic quadrajet from a parts house is not a good idea. Each quadrajet was jetted and tuned and air jets calibrated at the factree for the particular motor it was installed on. These carbs are very vacuum sensitive for tuning. These large carb rebuild facilities take a bunch of quadrajets from all different size and year's motors, remove all the specific components, and give them two simple jetted tunes (small block, or big block). It will either run well or it won't and if it doesn't it will be a total bear to get it tuned correctly for your specific motor. What I recommend at this point is to send it back and try another one out. You might get lucky.

What you want is to rebuild your stock quadrajet carb with quality components, since it already has the primary and secondary jets, orifices, hangers, etc. that your specific motor needs.

In your case, I think it maybe a vacuum leak, that is what it sounds like to me. I would check all surfaces when its running by spraying some carb cleaner, or WD40 around the mating surfaces and see if the idle raises. A vacuum leak becomes much more apparent when the motor is cold and needs the extra fuel richness.

[Greasey Harley]

Originally Posted by Caddylackn

You are not going to want to hear this: but putting on a rebuilt generic quadrajet from a parts house is not a good idea...

Fact.
That carb ain't never gonna run right.
Ever.

I hope I'm wrong, but I'm probably not.

[KQQL IT]

Mine was missing a pipe plug in a vaccum port in the rear by the base gasket

[Rich72C10]

Nice below 20 degrees here this morning. She started right up at level three choke this morning and zero indication of wanting to die.

I then let her race up a few hundred RPMs, slightly tapped gas pedal and she easily went into level 2 choke. Then let her even out a little more on the RMPs for a bit, slightly tapped gas pedal and easily went into level 1 choke.

Finally after a little bit more time at level 1 she evened out more and one last slight tap of the gas pedal, no choke and smooth as silk idle!


Soooo .... I think I have her nailed down on the choke! So much fun getting this figured out and having positive results. I totally learned something and thankful!

[RustyPile]

Originally Posted by Rich72C10

Nice below 20 degrees here this morning. She started right up at level three choke this morning and zero indication of wanting to die.

I then let her race up a few hundred RPMs, slightly tapped gas pedal and she easily went into level 2 choke. Then let her even out a little more on the RMPs for a bit, slightly tapped gas pedal and easily went into level 1 choke.

Finally after a little bit more time at level 1 she evened out more and one last slight tap of the gas pedal, no choke and smooth as silk idle!


Soooo .... I think I have her nailed down on the choke! So much fun getting this figured out and having positive results. I totally learned something and thankful!

Doncha just love it when a plan comes together!!

[Rich72C10]

Cue music.....