Engine stumbling/stalling in drive

[DaytonaJuckes]

I have an 83 c10 with a new 350sbc. It’s been running like a champ for the last 3 months. As I had it out yesterday I noticed it started to stumble after letting up on the accelerator and applying the brake coming up to a light and it progressed got worse to where it would die. The engine idle in park is at 950 and after dropping it into drive it will drop to around 650. It’s never done this before and I haven’t changed anything. Thought it might be a bad ground as it was hesitating when starting. Worked on all grounds and now it starts just fine but it still stumbles after putting it in drive. I haven’t changed anything and now it’s dying. Can vacuum leaks just start all of the sudden. I also have an Edelbrock AVS 2.

 

[fast 99]

Of course, vacuum leaks can be sudden as well as restricted carb circuits. Need to check both. Although I doubt it's the problem check fuel pressure and volume just to eliminate it. Idle vacuum steady?

 

[DaytonaJuckes]

Vacuum is steady when it’s idle in park. As soon as it goes into drive it will stumble and eventually die. Park idle is 950 and drive idle is 650. Should they be that far apart?

 

[fast 99]

Seems a bit more of a spread than is usual. Try adjusting the idle mix. Turn screws either in or out until highest RPM achieved then in 1/4 turn.

 

[DaytonaJuckes]

I reached over and grabbed my distributor just for ***** and giggles and it was lose. I set timing again to 12° advanced and set carb fuel mix from scratch. Took it for a spin and it seemed to have slight bogging down like there was carbon buildup in the exhaust. I romped on it and it seemed to clear things out and run smoother. It stopped stumbling and dying at stop signs. It’s running fairly smooth but it still seems to be idling high when in park and a smidge low when in drive.

 

[DaytonaJuckes]

I don’t know much about tuning these carbs so it time to learn. It seems like everyone has different terminology with carburetor components.

 

[fast 99]

I reached over and grabbed my distributor just for ***** and giggles and it was lose. I set timing again to 12° advanced and set carb fuel mix from scratch. Took it for a spin and it seemed to have slight bogging down like there was carbon buildup in the exhaust. I romped on it and it seemed to clear things out and run smoother. It stopped stumbling and dying at stop signs. It’s running fairly smooth but it still seems to be idling high when in park and a smidge low when in drive.

Be sure and check that both advances work.

 

[77Dmax]

Did you unplug the vacuum advance when you set the initial timing?

 

[DaytonaJuckes]

I did not. I’m learning a lot of this as I go. Didn’t know to unplug the advance. What does that do?

 

[DaytonaJuckes]

Be sure and check that both advances work.

Both advances? I better look up a couple videos.

 

[ChuckN]

You have two advances- one is under the distributor cap, the rotor is screwed to it. It is spring loaded (you’ll see that if you take the rotor off) and is a centrifugal advance. The rotor should turn in your hand and stop, and when you let it go, it should spring back.

The other is a vacuum advance- it is at the base of the distributor- It should be hooked up to the base of the carb via hose. The engine vacuum actuates it, and adjusts timing depending on how much vacuum it receives.

That’s a pretty basic explanation to get ya started.

 

[fast 99]

timing is set with vacuum hose disconnected, if rotor does not spring back that advance is stuck and needs repair

 

[77Dmax]

I did not. I’m learning a lot of this as I go. Didn’t know to unplug the advance. What does that do?

Pull the vacuum and check it again. The vac adance skewed your numbers. It'll probably smooth out after you readjust.

 

[DaytonaJuckes]

That’s what I like about these groups, I always learn a little more each time I have an issue. Had no idea about the secondary advance. I thought it was all vacuum assist

 

[DaytonaJuckes]

Thank you all for the assistance!!!