Low RPM Stumble

[hudson10]

I just picked up my first Jeep, 79 CJ7 with the AMC 304 /GM Turbo 400 combo, drove it 130 miles home with no issue Saturday, now come yesterday it developed a sight shudder at low rpm right at take off then goes away. Today it has got worse, it now falls on its face and misses, stumbles at low rpm then will take off. Also I dont know if its connected but when this started getting bad the tach quit working and will read once every couple minutes for a only a second or two and quit again. This is my first carb'd vehicle, any advice on where to start?

 

[Torxhead]

My first guess would be in the accelerator pump on the carb which could be leaking, worn, or out of adjustment. Hopefully it is not an electrical or ignition related problem. The tach issue could be from the engine stalling out, which is from not enough fuel from that pump to the engine during takeoff.

 

[Woolyworm]

What's on it for a carb? Acc pump is a good starting place. How long has it been sitting before you picked it up? Does it shudder as you move the carb slowly off idle by hand from the engine bay or just when driving? What does it have for ignition? Stock? When's the last time it had a tune up-plugs, cap and rotor etc?


Wooly

 

[Woolyworm]

Here is a good article on the basics of carb operation - not sure of your background- sry if your beyond this already but it's s good read anyhow.

http://www.superchevy.com/how-to/83118-carburetor-basics/


Wooly

 

[Lumpy Grits]

Does the coil still have the 'horseshoe' clip connector?
They are VERY problematic and not the best.
When was the last time the jeep was driven any amount before your bought it.
CK the oil level in the tranny-TH400s will shake a bit when they are low.
Do you know how to ck the oil level of an automatic tranny??
I would also be look'n for vacuum leaks. Make sure ALL of the intake and exhaust manifold bolts are TIGHT. Ck all vacuum hoses and their connections.
LG

 

[caveman]

On my buddies 81 CJ7 /AMC 258 i6 / 4.2l It won't run with the tach unhooked. When we rebuilt his jeep we tried to start it before we got all the dash wired up and after hours of trying to figure it out we finally hooked up the tach and off it went. Tried it again with it unhooked just to verify that that was the problem.
I don't know if this is related to your problem but keep it in mind since you are having problems with the tach. You may be able to by pass the tach to see if that's your problem.

 

[Posi]

You may be able to by pass the tach to see if that's your problem.

^^ this, it only takes a min to bypass the tach to rule it out.