engine stumble and start problem after warm

[escobar]

When the engine is either cold or hot on my 76' AMC 258 i6 / 4.2l , it likes to stumble or hesitate badly when i press the pedal down too quickly.

Ign advance is working, new hose. Motorcraft 2150.

Got the jeep with this problem a few days ago, hesitant to tamper with the dist timing until I get your opinions.

Also, after the engine is warmed up it doesnt like to start after a few mins. Ive read up on the vapor lock possibility but I dont think thats the problem. Its just to cold and the fuel lines dont run anywhere close to the exh. manifold or engine block.

Can you guys help me with some diagnosing tips that I can perform.

Btw, not sucking up- but this site is amazing.

 

[Old Dog]

I'd start by checking the choke and the accerator pump, also check for vac. leaks.

 

[escobar]

You might have hit something with the vac leak idea.

I've worked on my share of engines and didn't like this but thought it was an amc thing. The pvc hose goes to a 'T' connector that's between the pwr brake vac and carb. I disconnected it and looked for a carb port but there isn't one. The air intake filter housing is aftermarket and has no port either. I took the top screw of the filter lid off and put the pcv hose to it but apparently it wasn't enough pull and oil smoke came out of the v.c breather. Probably a sticky pcv. Carb is a MC 2150.

Didn't get much of a chance to run it before I left home but I'll see if the vacuum fix helps.

What might cause the hard starting?

 

[jeffgtoman]

I'm betting the accelerator pump is not putting out anything. That would cause all the problems you describe. You're probably able to get it started cold with the help of the choke. Once it warms up, the choke is open and there is no extra shot of gas for starting. Without the accelerator pump, it will always stumble on acceleration.

 

[escobar]

Well, the choke never closes but she starts and runs (idles), she'll also accelerate pretty well once you ease the pedal down the first 1/4 of throttle or so. Acc pump does feel a little 'dry' or more stubborn to move than others I've worked on.

Do part stores carry replacement parts for motorcraft 2150's? I guess I'll call and see.

Looks like the choke was manual just unhooked- just gonna put a bi-metal in there or maybe electric.

 

[escobar]

Well called them and they couldn't find the carb with a vehicle type and model, year.

I'm guessing ford, maybe a 300 I6? Not sure of year.

Anyone know?

 

[polish85]

Let me know if you figure out the problem bc i have the exact same thing happening. The only difference is that i have zero problem starting it at first. I just ordered a new distributor and will see if that works. Lately ive had a problem with my choke cutting back in after it warms up. If the new dist fixes the problem i will let you know. Going to look into this on saturday.

 

[polish85]

#2 could be a couple different things, oil on the flywheel, or broke spring in the pressure plate. both can cause it to shake when you let out on the clutch, i think a worn out pilot bushing can cause same thing. i'm assuming its a manual tranny.

Read more: http://www.jeep-cj.com/forums/f2/rough-start-when-first-cranking-up-7800/#ixzz1CFQY8PiO

this is what Cheepjeep said the problem might be when i posted in another thread.