Trouble with carbureted SBC Truck

[Just a guy who likestruck]

I have a small-block Chevy with a Rochester 4-barrel carburetor. The truck idles fine, but as soon as it’s put in gear, it stalls or tries to stall. I’ve cleaned out the idle circuit, used premium non-ethanol gas, and checked for vacuum leaks but found none. I’ve also installed new spark plug wires and plugs. I’m at a loss trying to figure this out. Any suggestions to try and fix the issue.

 

[DuckRyder]

Q-Jet or 4 Jet or something else?
Automatic?
Timing?
Idle speed?
Engine/Trans stock?

 

[Just a guy who likestruck]

Q-Jet or 4 Jet or something else?
Automatic?
Timing?
Idle speed?
Engine/Trans stock?

Q-jet
350 turbo
It idles fine so I’m assuming timing is correct. I don’t have an rpm gauge to check l.
Stock 81 motor and trans

 

[supton]

Vacuum leak? time to get some gauges.

 

[DuckRyder]

81? Does it have an MC Solenoid / ESC?

 

[Brian123]

Q-jet
350 turbo
It idles fine so I’m assuming timing is correct. I don’t have an rpm gauge to check l.
Stock 81 motor and trans

Have you changed the Fuel Filter?
Check for Vacuum Leaks again and if you still have an issue, replace all of your Vacuum Lines.
New Distributor Cap and Rotor?

Thought of something else, on the Turbo 350 trans there is a Vacuum Modulator near the transmission so you might need to check that or replace it, as well as looking at the line that goes from the Trans to the Carburetor.

 

[DuckRyder]

Also - are the mixture plugs knocked out if it ever had them?

Check distributor for sticking / weights, weak springs / red death.

 

[zrxkawboy]

Does the problem show up when the engine is only cold, only hot, or both?

 

[Just a guy who likestruck]

Does the problem show up when the engine is only cold, only hot, or both?

When it’s cold it takes like 5 try to get it to idle, hot it idles fine.

 

[chainblu]

I would try a few degrees more timing and see if that helps.

 

[zrxkawboy]

When it’s cold it takes like 5 try to get it to idle, hot it idles fine.

Choke operation ok?

 

[Brian123]

When it’s cold it takes like 5 try to get it to idle, hot it idles fine.

There is a choke rod on your carburetor, make sure this is working. You might need to spray some carb cleaner on it. I would also spray all of the Carb Linkages. Also make sure the PCV is clear and all of the hoses leading to the PCV are clear.

 

[eljefino]

Pull the carb and see how the "transfer slots" look at the throttle blades; They should be little squares, not rectangles. Often older carbs start stalling so people turn up the idle over and over again, opening the transfer slots. This causes the carb to not get a good signal for just-off-idle. A symptom of this is the mixture screws "don't do anything."

You can also try both ported and non-ported vacuum for your ignition advance.

Are these units known for throttle shaft wear? Spray that area with carb cleaner when running to see if there's a vacuum leak.

 

[Exhaustgases]

Broken wire ?

 

[Oldswagon]

Stalling in gear is likely an indicator of a lean condition. If this is when the engine is cold, it could be as simple as the choke pull off not working properly or being out of adjustment. This seems to be a super common issue with these carbs as everyone has forgotten how to adjust a choke properly. If it is stalling out in gear even when the engine is fully warmed up, it's probably another issue. Check for vacuum leaks, ensure all hose are connected and not cracked. The throttle shaft bushings on a Q-jet will wear out and cause a leak at the throttle shaft.

If all that checks out, ensure your timing is set correctly and then check the idle mixture. Don't "assume" it's correct. You can set the idle mixture fairly easily with a vacuum gauge. Another issue I came across on an Olds 88 with a Q-jet years ago, was the charcoal filter on dumped a bunch of carbon pellets in the carburetor fuel bowl. This lead to the engine being super lean due to fuel starvation and wouldn't run in gear unless you two footed it. I had to pull the top off the carb and clean out the fuel bowl.

 

[tbm3fan]

Sounds to me like a carb problem. I have six cars with carbs although they are all Autolite and I know their in's and out's. Don't know Rockchester but the guy in the video below does. I get all my carb parts from Mike's.

 

[chemman]

Have you checked for adequate fuel flow going into the carburetor? You should be able to fill a quart container in less than 30 seconds or so.

 

[Gasbuggy]

Little internal filter need a change?

 

[97prizm]

I have a small-block Chevy with a Rochester 4-barrel carburetor. The truck idles fine, but as soon as it’s put in gear, it stalls or tries to stall. I’ve cleaned out the idle circuit, used premium non-ethanol gas, and checked for vacuum leaks but found none. I’ve also installed new spark plug wires and plugs. I’m at a loss trying to figure this out. Any suggestions to try and fix the issue.

You mentioned when you shift into gear. Maybe an issue with the shift solenoid, idle air control valve, or fuel flow. Does it go away if warmed up?

 

[emmett442]

Happened suddenly? If so, I wouldn't try to tune it out with adjustments. It'll never be right if you don't find the actual problem.

When it’s cold it takes like 5 try to get it to idle, hot it idles fine.

Check that choke pull-off is working. It should crack the choke open slightly after starting.