rochester quad question, stalls during warm up

[ciffer]

the k10 stalls during warm up at idle unless i keep slight pressure on the throttle. i am not sure what model. once the engine is warm it idles like a champ.

it has an original rochester quadrajet. i think the carb is from the 1972 donor vehicle, not the original 305 but i am not sure.

the engine will also sometimes stumble off idle and almost stall, it will do it at all engine temps but is worst when cold. stumbling is more common after idling at a light, worse if it was a long light.

the weather has been pretty cool lately.

 

[lectric80]

I have been having an issue with mine that sounds a bit similiar, and I found a major vacuum leak that seems to be the issue. Have you verified that all the vacuum lines are intact? That's probably the first place I would check.

 

[mdm365]

Yes check for vacuum leaks as stated ^^^ But also sounds like the choke/hi idle/choke pull off is not right .These are very related!!

The pull off should pull the choke plate open at lest an 1/8 inch from open when is started cold,Also make sure the choke is pulling open when it warms up.There is an hi idle adjustment on the left side under the choke housing( a small Phillips ) to adjust the hi idle.

As far as the stumble 1st thing is check the timing and vacuum advance make sure no issues there.I would bet the accelerator pump is bad or not adjusted properly.


Mike

 

[mnstrburbon]

You may also need to adjust the idle air bleeds on the front of the carb requires a special tool on most. You might have the standard flat head ones take a look warm engine and set to best idle or with a vacuum gauge to highest reading. If carb motor or cam air filter have been changed from stock theirs adjustment will solve a lot of problems.

 

[ciffer]

I have been having an issue with mine that sounds a bit similiar, and I found a major vacuum leak that seems to be the issue. Have you verified that all the vacuum lines are intact? That's probably the first place I would check.

i'll take a look. fortunately the truck doesn't have much for vaccum lines, so it should be easy to check.

The pull off should pull the choke plate open at lest an 1/8 inch from open when is started cold,

do you mean 1/8th inch from closed?

As far as the stumble 1st thing is check the timing and vacuum advance make sure no issues there.I would bet the accelerator pump is bad or not adjusted properly.

Mike

i believe the accelerator pump was replaced very recently. timing was also set recently by the mechanic that installed the engine. regardless, what do i do for checking them? how do i find out what the correct timing is for a non-original engine?

 

[mdm365]

i'll take a look. fortunately the truck doesn't have much for vaccum lines, so it should be easy to check.



do you mean 1/8th inch from closed?



i believe the accelerator pump was replaced very recently. timing was also set recently by the mechanic that installed the engine. regardless, what do i do for checking them? how do i find out what the correct timing is for a non-original engine?

Yes an 1/8 inch from closed That depends on what you have ie stock 350,383-- cam, ect. to check the vacuum advance you will need a timing light with a dial on it or you can put the light on and apply vacuum to the advance hose and see if it advances.

As far as the pump goes its possible that the rubber on the pump got rolled over when it was installed(I spray some wd 40 when I install them) The other thing is there is an adjustment on the arm where the rod attaches you might move it to the next hole and see what it does.I will post up some other info after work to night for you on the q-jet and timing stuff.

Mike

Mike

 

[El Larry]

Also check that the throttle shafts are not worn, they can cause a vacuum leak. Happened to three people I know, cars ran like crap when cold, and had a rough idle. Just replaced one on my buddys Eldorado this week for that reason. Just a thought~

 

[ciffer]

i took the air cleaner housing off and took a look at the vacuum lines. i can only see three lines, one to the distributor, one to the secondary and one to the PCV valve. *edit* looked again, there is a fourth running to the power brakes. all the line are new, they all looked well seated. while the engine was idling i could hear a hiss, is it just the carb making the hiss?

advance note, the truck had not run since last night. with the cleaner off, i moved the throttle enough to close the choke, bumped the starter and it fired right up then stalled, bumped it again and it fired up again. i got around to the engine bay, the choke was completely open, engine started to slow so i closed the choke a little and the idle smoothed. i repeated that a couple times, after that the engine idled very well (although it seemed a bit fast) with the choke open. could the choke fully opening right after start up be causing the stalling?

 

[ciffer]

bump

 

[mnstrburbon]

If you hear a hiss that tells me vacune leak which you say there is none. Or the idle air bleeds are set wrong when removing all the smog and extra vacuum lines the carb now has less vacuum resources at idle and therefore the idle air bleeds need to be re adjust. Most common overlooked part of carb tuning my.02 i already posted this also.

 

[ciffer]

i'll check the idle air bleeds. besides vacuum lines, what are common causes of vacuum leaks? carb to manifold gasket?

would a vacuum leak cause the off-idle stumble?

 

[mdm365]

How you doing with the carb issues ??? I have been working some long days this last week but Here is a good read with pic and all,not mine but detailed.
Here

I had a hissing issue with the last carb and found these two of these tubes down in the carb just tapped them back in all was good.

Vacuum leaks can come for any of the carb gaskets,primary and secondary shaft bushings.

Mike

 

[fmstruck]

i took the air cleaner housing off and took a look at the vacuum lines. i can only see three lines, one to the distributor, one to the secondary and one to the PCV valve. *edit* looked again, there is a fourth running to the power brakes. all the line are new, they all looked well seated. while the engine was idling i could hear a hiss, is it just the carb making the hiss?

advance note, the truck had not run since last night. with the cleaner off, i moved the throttle enough to close the choke, bumped the starter and it fired right up then stalled, bumped it again and it fired up again. i got around to the engine bay, the choke was completely open, engine started to slow so i closed the choke a little and the idle smoothed. i repeated that a couple times, after that the engine idled very well (although it seemed a bit fast) with the choke open. could the choke fully opening right after start up be causing the stalling?

Yes. Every Qjet I have ever had is really cold blooded if the choke isn't working right. Does this have a heat stove choke or an electric choke?

Also, carburetors are going to hiss to some extent just by their nature. Sometimes vaccuum leaks are really hard to find because of this. With no more vaccuum lines than it sounds like you have, I would say about the only place you could still have one would be under the carb on the base gasket. I have seen them get a chunk blown out of them on a backfire.

 

[Big Ray]

q-jet tech

link

link

parts

parts

more parts

parts and tech


these should get ya where you need to be!

p.s. I saved these links from other threads here, so thanks to all who posted. this place rawks....

 

[NEK5]

q-jet tech

link

link

parts

parts

more parts

parts and tech


these should get ya where you need to be!

p.s. I saved these links from other threads here, so thanks to all who posted. this place rawks....

yes it does!

 

[ciffer]

How you doing with the carb issues ??? I have been working some long days this last week but Here is a good read with pic and all,not mine but detailed.
Here

I had a hissing issue with the last carb and found these two of these tubes down in the carb just tapped them back in all was good.

Vacuum leaks can come for any of the carb gaskets,primary and secondary shaft bushings.

Mike

haven't had a chance to get to the carb. i was given a 93 Achieva a few days ago; i have been working on getting it ready to sell. i am watching this thread closely though, and taking note of everything said.

Yes. Every Qjet I have ever had is really cold blooded if the choke isn't working right. Does this have a heat stove choke or an electric choke?

Also, carburetors are going to hiss to some extent just by their nature. Sometimes vaccuum leaks are really hard to find because of this. With no more vaccuum lines than it sounds like you have, I would say about the only place you could still have one would be under the carb on the base gasket. I have seen them get a chunk blown out of them on a backfire.

i checked the numbers on the carb, 7042208, so it is the carb that shipped on the 1972 donor vehicle, federal emissions, auto trans.

it has the heat stove type choke, although i think there is a pipe that is missing. regardless, the choke immediately pulls fully open. please correct me on this, but it seems like if the spring were functioning correctly without the heat pipe, the choke would open slightly but never fully open when the engine is warm.

knowing the owner, i would seriously question whether or not the carb was properly torqued to the intake manifold that last time the carb was installed.

another note i have neglected to mention is that once in a while the engine will diesel briefly after shutting off the ignition. this is very brief, lasting 1 second of less.


i am thinking of taking a propane torch (not ignited) and blowing propane around the area of the base gasket and vacuum ports to see of that changes the way the engine idles.

 

[Kenny78]

i am thinking of taking a propane torch (not ignited) and blowing propane around the area of the base gasket and vacuum ports to see of that changes the way the engine idles
PLEASE JUST USE CARB CLEANER!!! Spray a small shot straight down the intake to see how it responds.

it has the heat stove type choke, although i think there is a pipe that is missing. regardless, the choke immediately pulls fully open. please correct me on this, but it seems like if the spring were functioning correctly without the heat pipe, the choke would open slightly but never fully open when the engine is warm. I thought a 1972 would be a divorced choke. Does your manifold have a corresponding hole for the pipe in the manifold? If not but does has that black cover it would be easy to convert to electric.

another note i have neglected to mention is that once in a while the engine will diesel briefly after shutting off the ignition. this is very brief, lasting 1 second of less.

The choke not working/being connected will explain every problem you have

 

[Cubman]

I am having similiar problems on my '78 K10 with the 4 barrel rochester. My choke was staying closed all the time, but everything was free, so I thought it was the choke thermostat. The thermostat was not the problem, it looked like it was working just fine. Could the manifold be plugged up underneath the thermostat, not sending it any heat? For now I have the choke zip tied all the way open, and it takes slight pressure to keep it running.
The truck idles pretty high, I just put in a tach and it reads around 1200-1300 at idle. I also have an occasional dieseling problem. It is still there after 1.5 cans of sea foam and new spark plugs.

 

[ciffer]

I thought a 1972 would be a divorced choke. Does your manifold have a corresponding hole for the pipe in the manifold? If not but does has that black cover it would be easy to convert to electric.

yes, it does have the heat riser on the manifold.

the choke pull-off looks very similar to the one on this carb.
http://cgi.ebay.com/ebaymotors/ws/e...&sspagename=mem_guide:4&category=33550&ih=022
the casting number is different from mine, so i don't know if the rest of the carb is the same.

it does not have the black disc on the side like this one.
http://cgi.ebay.com/ebaymotors/vint...ies?hash=item3a52827b04&_trksid=p4506.c0.m245.

 

[Kenny78]

Ok, never had to do this(specifically avoided it for this reason) but the carb you linked that was similar to yours is a divorced choke. You might google to get an idea of whats needed. If your manifold has what I think youre saying, theyre not compatible. Carburetion.com
Divorce Choke Conversions
Converts divorce choke Quadrajets to electric chokes mounts to intake manifold CU44570-78
Small Block
Chevy car and Chevy -GMC truck

That might work to get you a choke if your manifold doesnt have the divorced choke boss.