1984 C10 305 stall at low speeds, loss of power during accel

[BucketofBoltsBob]

Did the 1984 305’s have electronic spark control? Some of what you describe reminds me of my 305 with the ESC working (poorly!). Do you happen to know if you have an intact ESC distributor? It’s the one with the extra (grey) four wire connector out the side of the distributor. I might try bypassing the esc to see what that does if it’s still intact. Bypass it by cutting the green and black wires and connecting the distributor side cut wires together.

I would check vacuum lines, clean fuel, carb, etc, but it sure sounds like a spark issue to me at first read (and that’s of course because I have seen this type of behavior).

I do believe I have an intact esc distributor. I have not tried the fix you suggested just yet. But rebuilding the carb did seem to fix most of my issues along with the small vacuum leak repair. What exactly would bypassing the esc do? I would like to know just incase it becomes something I have to do in the future. Thanks!

 

[BucketofBoltsBob]

Thanks again for all the replies and thoughts, I appreciate it and I have fixed my notifications so I will get notified and be able to respond to any replies moving forward that was on me my bad.

 

[GTX63]

I read thru your initial post but not completely thru the second one, however I just have a simple question. You said the truck sat for over a year between blowing belts and hoses and the repairs.
You listed one possibility for the current driveability problem as bad gas. Have you drained the tank and replaced the fuel?
Also, if you use a Wix 33003 fuel filter, it is clear so you can see the condition of the fuel and filter.

 

[BucketofBoltsBob]

I read thru your initial post but not completely thru the second one, however I just have a simple question. You said the truck sat for over a year between blowing belts and hoses and the repairs.
You listed one possibility for the current driveability problem as bad gas. Have you drained the tank and replaced the fuel?
Also, if you use a Wix 33003 fuel filter, it is clear so you can see the condition of the fuel and filter.

I've topped off the gas with new gas but have not drained/ cleaned the tank and then replaced the fuel. I am using a basic duralast in-line fuel filter it is not clear. But the truck is running mostly smooth now except for the slightly high idle which I can't seem to figure out.

 

[GTX63]

Many times, actually most of the time, we outthink ourselves and try to skip to level 5 when it is almost always the simple stuff.
I would at a minimum drain the tank and top it off with leaded fuel. I'd throw a can of Berry Man B12 in the tank for good measure, and run it.
After the next fill up, if there isn't a noticeable difference, then move on to the next steps.

 

[BucketofBoltsBob]

Many times, actually most of the time, we outthink ourselves and try to skip to level 5 when it is almost always the simple stuff.
I would at a minimum drain the tank and top it off with leaded fuel. I'd throw a can of Berry Man B12 in the tank for good measure, and run it.
After the next fill up, if there isn't a noticeable difference, then move on to the next steps.

You think bad gas could cause a high idle issue? I do plan to eventually drop the tank clean and replace the old gas, but just hasnt been high on my list.

 

[GTX63]

I think you should do the easy stuff first. Yes, it could be a vacuum leak, or something else, but gas that is over a year old is low hanging fruit. Old gas gums up components in a carburetor, sticks the float, plugs filters, clogs pumps. I'm just saying start your process from the beginning, then you don't have to go back and forth, and forth and back.

 

[GTX63]

I had a guys GMC squarebody in my pole barn about a month ago. K15 350 quadrajet. It would not idle at all. Smoked so bad it looked like a wet leaf fire. Backfired thru the carb, hitting on about 5-6 cylinders. He said he was tooling down the road and it just started acting up. He had oil foulers in two cylinders. He wanted to jerk the motor and replace it. I'll admit that I also thought the engine was bad.
He didn't tell me at first that he noticed it was loading up a little at idle so he decided to rebuild the carb. He had never rebuilt one and totally fubared the job. It was dumping so much fuel the dipstick showed two quarts over full and the cylinders were washing out.
I checked compression, electrical and fuel and within about 45 minutes confirmed the carb was no good.
I put another quadrajet on it, changed the oil and the spark plugs and it is now running like it did in 1978. No smoking, no misfire, nothing.
The best troubleshooting follows a method, or a tree or a process, whatever you want to call it, but as a former ASE tech, random guesswork leads to frustrations and throwing wrenches, parts and money out the garage door.

 

[BucketofBoltsBob]

Ok i feel that. Knowing its probably not the issue but at least get it out of the way and one less thing to worry about especially if any other issues arise in the near future. Honestly im just being lazy and didnt wanna drop the tank since i read it could be a pain.

Thats crazy about the carb though. I did read a lot of posts on here and other sites about how just swapping the carb completely changed the way their trucks and cars ran making them feel like new. I did end up getting pointed to the carb for my repair too and doing the rebuild taught me a thing or two about patience and gave me a new respect for techs that actually do that for a living. Its not hard to do the rebuild in actually knowing the basic process but making sure everything is tuned and set properly is definitely work especially as i sit here with a still improperly tuned carb. Plus finding information on the specific carb model is a pain too. Im glad i didnt destroy my engine and although i know the engine will need to be replaced or rebuilt in the near future I am hoping to get some more life out of the engine and have it driveable in the meantime. Also definitely not trying to throw unnecessary money or time at it since its gonna need a lot of money and time already to bring the life back into it so i get the idea about following a process. Thanks for the input ill probably get around to that sometime this week hopefully.

 

[Steppin Razor]

So the stall issue is fixed with the carb rebuild, which makes sense given the problem with the speed bump. Probably dislodged some gunk that clogged a passage or needle, and now you're in the clear.

Current problem is the idle. You mentioned the mixture screws, but not the idle speed screw. Since this was your first carb rebuild, maybe go through the steps you did to tune with the vacuum gauge. You kind of have to go back and forth a bit with the speed screw and mixture screws. At least on my Edelbrock I did. If you're doing it with the air cleaner off, putting it on will make a small change in airflow, causing the mix to get a bit richer.

 

[BucketofBoltsBob]

So the stall issue is fixed with the carb rebuild, which makes sense given the problem with the speed bump. Probably dislodged some gunk that clogged a passage or needle, and now you're in the clear.

Current problem is the idle. You mentioned the mixture screws, but not the idle speed screw. Since this was your first carb rebuild, maybe go through the steps you did to tune with the vacuum gauge. You kind of have to go back and forth a bit with the speed screw and mixture screws. At least on my Edelbrock I did. If you're doing it with the air cleaner off, putting it on will make a small change in airflow, causing the mix to get a bit richer.

So right now the normal idle speed screw is fully backed off but I still wasnt getting any lower than 900rpm. So thats what made me think vacuum leak. I did kinda want to adjust the mixture screws in till i created a lean condition and then back them off to max vacuum. I have been working with the cleaner off since its impossible to get to the mixture screws with it on but i will try that. I havent been able to get back out to check it out again just yet.
One thing that did catch my eye when I was watching a carb tuning video was that when the electric choke disengages and the fast idle switches to normal idle that the arm that the normal idle screw presses against is supposed to well press against the screw and while the choke is engaged during the first 30 seconds or so its not supposed to be against the normal idle screw (thats what i got from the video not sure if thats correct).
So i noticed that theres still a gap between the arm and the normal idle screw screw-hole. Meaning i can back fully off the idle screw and not have it be back inside the screw hole maybe like 1/16-1/8in gap(hope that makes sense). I kinda mentally noted that so it makes me wonder if maybe my choke isnt disengaging properly (like wrong choke adjustment) and that might be part of the issue? I will be adding what you said to the list of things to check though and try to play around with the tuning as well

Here is my current list of things to check:
- check for vacuum leak especially around baseplate of carb (incase of overtightening screws) and intake manifold
- slight rich condition through mixture screws
- electric choke function and adjustment
- idle speed screw tuning with air cleaner on

 

[Steppin Razor]

I can't get to mine with the air cleaner on either, so I just go a tad richer when setting it because I'm no rocket scientist

 

[BucketofBoltsBob]

Ok so quick update:
I am still troubleshooting the high idle i did find a small vacuum leak at the carb base plate but from undertightening not overtightening. But my idle is still high between 800-900rpm at normal operating temp.
One thing ive noticed is that when i first start it “cold start” it has a low idle 600-700rpm during the time that should be fast idling then as it heats to operating temp it increases to the 800-900rpm range which is where it currently stays at. Ive tried messing with the mixture screws and tuned to max vacuum which is between 19-20inhg.
The normal idle speed screw is fully backed off and still the idle remains between 800-900rpm. Ive included a picture of it fully backed off taken while idling once warmed up and you can see the gap i dont know if thats normal.
If the gap is abnormal could this be an issue with the electronic choke? Ive read a few posts about issues the electronic choke can cause.
If not the other main issue that comes up when i search the system is another vacuum leak but considering I’ve already went through most the hoses and around the intake manifold and base plate i have no clue where it could be. I even double checked these areas after repairs to make sure there wasnt a leak still present.
If you have any ideas what it could be, all input is appreciated. Thanks

 

[BucketofBoltsBob]

Alright so I fixed 2 issues and I found potentially one. Now my engine is idling at about 850rpm in Park and 550 in Drive or Reverse. Is this within normal range for a 305 or would this still be considered high?

The first issue I fixed was my rear vacuum break connecting rod didn't seem to be operating correctly so the fix for that was just bending it so that it could actually be pulled when the rear vacuum break pullled a vacuum. Simple enough.
The Second issue was an error that was completely avoidable but I obviously didnt read the instructions as thoroughly as I should have and went straight to the video tutorials. This issue was the cam secondary lockout not in the right position so it actually never locked out anything and was just kind of there. (I'll include pictures of the before, after, and where i finally noticed my issue in the instructions).
But this lead me to my potential issue.

After reinstalling the carb which I had to remove to perform repairs the car seemed to operate smoothly fast idle started around 850 and moved up to just above 1000 before it warmed up and kicked over to curb idle. and curb idle was at 800 in Park at fully pulled back. However, in drive it was only at 500 rpm which made the engine run a little rough and seem like it had the potential to stall. So I pushed in the idle speed screw a little to up the idle to 850 in Park and 550 in Drive and now its sounds nice and is running clean and no longer sounds like it wants to stall when put in gear.

The issue is the secondary choke plates (? not sure on correct term, not the throttle plate) didn't seem to be opening after warm up at full throttle given. This is what lead me to even check the secondary in the lockout in the first place because I thought maybe it was getting caught due to improper installation, which turned out to not be the case. I will say that the engine was running for about 10 minutes or so. My thermostat has midway at about 210 although I read that operating temp is about 195. My engine was under 210 when I checked and near enough that I would have assumed that it was already at operating temp. It is a hot 95 degrees already outside today. But even when i pressed the throttle all the way by hand using the throttle linkage (rpm 2100+ but not held there for more than 5 seconds max) the secondary choke plates never moved.

So my questions now are:
1. Is an 850 in Park and 550 in Drive an okay idle setting to leave the engine at?
2. Is there anything that I am doing wrong as far as getting the secondary choke plates to open? Maybe not holding the throttle long enough or should I have let it ran for longer to let it warm up more before I tried? I will continue checking it out and see if I missed anything.

 

[Rusty Nail]

Did you ever change the oil?