New (to me) 81 Jimmy, and it's issue

[usagi]

First of all, Here is the beast:

I know, Chrome's gotta go. And it will with time, but that's not the top of the list, yet.

Let me start by saying that I have a bit of a learning curve to overcome with this. I'm not auto-ignorant, but I'm no home-garage master mechanic, either. I fit somewhere in between (probably closer to the lower spectrum). So I will need some "pretend I'm 6yrs old" type of instructions.

Basically, what is happening is that the truck stalls off idle. Whether it be sitting still in Neutral/Park or accelerating from a stop-light, it either hesitates or completely dies when I first press the go-pedal. Usually, if I feather it just right to get it moving, it'll run fine through the rest of the RPM range. It'll also sometimes completely stop exhibiting the issue once it has warmed up and been run for a while.

I had been told that this could potentially be caused by a bad distributor, or moisture getting to the connections. I went ahead and replaced the cap, rotor, wires, and plugs to no avail. There were also a lot of vacuum lines with busted connections, which was fixed by my mechanic. It seems to run quite rich, judging from the smell of things, but I have very limited (read:none) experience tuning carbs. No time like the present to learn, though.

I've searched through a few threads regarding similar issues, and have a couple ideas of what to check. First is another sneaky little vacuum leak. What is the best process to seek them out? Another process that seemed to work for someone was "advancing" the Distributor cap. What, exactly, should I do to attempt this? The third thing I've seen is that it might be one of many issues with the carb. Choke stuck, idle too low, AFR off, etc. Where do I start and what are my steps to take?

Any other suggestions are very welcome and appreciated. Just remember "pretend I'm 6yrs old". I've already put in the payment for my membership, because I know I'll be getting help here and it's only fair that I pitch in. Thanks in advance.

 

[scottsdale86]

What kind of carb? I am assuming if its a stock rig then a Rochester Quadrajet. If that is the case it sounds like it could need a rebuild. It could be the baseplate issue as well as they are sometimes prone to warping or cracking so it would be best to have it rebuilt by a seasoned pro.

 

[usagi]

What kind of carb? I am assuming if its a stock rig then a Rochester Quadrajet. If that is the case it sounds like it could need a rebuild. It could be the baseplate issue as well as they are sometimes prone to warping or cracking so it would be best to have it rebuilt by a seasoned pro.

I believe it is the stock carb. I'll have to check when I get home to make sure.

 

[scottsdale86]

If you decide to tackle it yourself get these books:
http://www.amazon.com/Rochester-Carburetors-Doug-Roe/dp/0895863014
http://www.amazon.com/Rebuild-Modify-Rochester-Quadrajet-Carburetors/dp/1932494189
Just don't mess with the Adjustable Part Throttle APT on the carb. They come set with 2 turn out from the factory. Here is a good link to tuning these carbs http://www.73-87.com/7387garage/drivetrain/myqjet.htm There are links in red that are good to read too.
These carbs are good carbs but most don't know how to tune or build them. In fact they are the best carb you can get as far as power and economy you can get for a 4wd vehicle. Of course you could go FI but then that is a whole different issue.

 

[teacher_dave]

Toss that Quadrajet junk (I love a good running q-jet and they are awesome when correct). You can get a NEW edelbrock 1406 performer carb that will be great on your motor for the same $$$as a remanned (by who knows who and who knows how well) Q-jet. And when the time comes, you can redo the 1406 yourself (basically just a carter AFB carb) with a screwdriver and a pipe cleaner.

Dave

 

[scottsdale86]

Yeah the old AFB (carter or edelbrock) are good street carbs that you can generally bolt on and run. However any real inclines or off angle driving and they struggle just to stay running. They just arent designed for it. Read this first. http://www.4wheeloffroad.com/techarticles/off_road_carburetor_review/index.html The edelbrocks and carters just dont do well offroad. Not that they are bad carbs just not ideal for off road use.

 

[teacher_dave]

Yeah the old AFB (carter or edelbrock) are good street carbs that you can generally bolt on and run. However any real inclines or off angle driving and they struggle just to stay running. They just arent designed for it. Read this first. http://www.4wheeloffroad.com/techarticles/off_road_carburetor_review/index.html The edelbrocks and carters just dont do well offroad. Not that they are bad carbs just not ideal for off road use.

Thanks for correcting me. My experience with them has been limited to street/ strip drag racing with my 81 Camaro.

 

[scottsdale86]

No they work well on street rods. I am running 2 750 AFB's on an edelbrock low rise dual quad manifold on my big block powered chevelle. Work great on it. Not so much on my 86 when i bought it. Thats why i went back to the quadrajet.

 

[badmix]

Im going to say its your carb and the accelerator pump, so either rebuild the carb or get a new one.

 

[usagi]

Thanks for the responses guys. I'm going to start with a rebuild kit once I verify the part#, since that seems to be the most economic path while also giving me a chance to get wrist deep in the carb to learn. Having both a carbed truck and dirtbike, I'll be getting wrench-time one way or the other. If there are any more ideas, keep 'em coming.

 

[badmix]

This will turn into an "Onion" for sure. If you rebuild the carb, check out the vacuum lines (even though you said mechanic replaced them) also look at all your rubber fuel lines, etc

 

[scottsdale86]

Yes if it is stock early 80's GMC and chevy trucks/blazers used vacuum for alot of things. Go over them with a fine tooth comb. also check the plastic lines coming from the charcoal canister. Those get brittle over time and can cause leaks as well.

 

[Jessie James]

Im going to say its your carb and the accelerator pump, so either rebuild the carb or get a new one.

I'll second the accelerator pump.

When you first press the gas down, the accelerator pump shoots a little squirt of gas into the throttle body. This helps prevent the truck from dying. Based on your description, I would replace that FIRST. It's cheap and easy, and is probably on the outside of the carb somewhere. You may be able to replace it without taking anything off the truck.

Rebuilding a carb is really easy. Most rebuild parts kits include directions. Take your time.

Just keep all the screws in their holes after you take it apart so you don't lose any of them. Also remember that most carbs are made of softer metal so don't crank down the screws to much - just hand tighten - or you'll possibly strip the threads out.

Words of warning:

1. Wear latex gloves.

2. Work outside. Do NOT breath the fumes from carb cleaners. Use OUTSIDE only. I used to do this work inside, and now I have lost my sense of smell and have a strong (bad) reaction to anything chemical smelling - if I can smell it. For example, I can't smell smoke, which won't be handy if there is a fire in my house ...

3. Do NOT use brake and parts cleaner on your carb while on the engine - especially if it's running. If it gets burned in the engine, it creates chlorine gas - and LOTS of it. I nearly died with that life lesson.

So, anyway, try that $10 fix and let us know what happens.

 

[scottsdale86]

If i am correct that year didn't have the mixture control solenoid. However It MIGHT have had the accelerator pump solenoid on the passenger front side of the carb. It will have a connector and wires leading to a sending unit on the thermostat housing. It basically richened the A/F mixture up while the engine was cold and then closed when the engine got up to operating temp. Hence the wiring leading to the thermostat housing. If it does have this system then take care of the connectors as they break of easily after 30 years of hot/cold cycle. Its an OK system but i prefer the standard federal emissions carbs as they didn't have that system. It just complicates things and can lead to a WAY over rich condidtion that will foul out plugs and give sluggish perfromance similar to what you describe.

 

[usagi]

I'm probably going to give this all a go on Sunday if I can find the rebuild kit in stock near me.

This will turn into an "Onion" for sure. If you rebuild the carb, check out the vacuum lines (even though you said mechanic replaced them) also look at all your rubber fuel lines, etc

I'm assuming I should follow each line from beginning to end to check visually for loose fit/cracks. Is there any trick of the trade I can use to find some of the less obvious sources? I've seen mention of spraying carb cleaner in some way, but what exactly should I try to accomplish with this method?

 

[tRustyK5]

i'm gonna go against the grain here and say your choke needs adjusting. Most Accel pump issues don't get better when the engine warms up. Choke stuck wide open is a biatch when it's cold, but gets better and better as the engine warms up.

Rene

 

[usagi]

i'm gonna go against the grain here and say your choke needs adjusting. Most Accel pump issues don't get better when the engine warms up. Choke stuck wide open is a biatch when it's cold, but gets better and better as the engine warms up.

Rene

Thanks. I'll check that, too. It does seem hit or miss whether it gets better as it warms up.

 

[badmix]

I'm probably going to give this all a go on Sunday if I can find the rebuild kit in stock near me.



I'm assuming I should follow each line from beginning to end to check visually for loose fit/cracks. Is there any trick of the trade I can use to find some of the less obvious sources? I've seen mention of spraying carb cleaner in some way, but what exactly should I try to accomplish with this method?

Vacuum line is so cheap. I would just wholesale replace it all. Cant always rely on what someone else did.

 

[teacher_dave]

I'd leave the Q-jet rebuild to the pros, especially if it's your first time. It's one of the most complicated carbs on the planet. Lots of meticulous adjustments and things to check for. Having done both, I personally think it is easier to rebuild an engine than rebuild a Q-jet.

Dave