Vapor lock

[redashi]

Greetings,

Recently started having vapor lock issues. A little background. The cj was running rough, rebuilt the stock carb and lost spark while tuning it, alternator was putting out 16+ volts and fried the computer. Did a nutter bypass and upgraded to weber carb since I couldn't get the carter to run good at idle with the stepper motors and replaced ignition components, ICM, coil, etc. Ran good for a couple months, then started idling bad again, then occasional stalls at a light. Noticed the exhaust manifold gasket near the carb was bad blowing exhaust right on it, thought that was the issue, didn't fix the vapor lock. Heard the aftermarket ICM are , changed again with no love.

Now the problem is worse. I can idle in the driveway all day with no issues, but when it is under load and the thermostat kicks in, it vapor locks but intermittently. Drive in the morning, good. Afternoon or evening, it dies but randomly. I live in Washington state, not real warm right now. Tonight it backfired flames after it died from vapor lock. Timing is at 8 btdc, carb idle is halfway between where it runs rough. Replaced and rerouted fuel lines away from heat sources, plus insulated the lines. I'm at a loss. Vacuum or electrical maybe? Hopefully someone smarter than me can point me somewhere.

 

[Peanut Butter]

Tonight it backfired flames after it died from vapor lock.

I think this rules out "vapor lock". The flames are due to unburned fuel vapor.

I would take a really hard look at the timing. Make sure the timing chain did not slip. The flames tell me that unburned fuel was blown out through the exhaust valves. Many AMC engines have a plastic & metal timing gear. The plastic part wears out and the timing slips. This is definitely a complicated process to check since you have to remove almost all of the front hardware to get to the timing chain. I think it would be worth it though. I found my chain very loose and the plastic/metal gear. Replacing all of it was easy and straight forward. You can see pictures at my build thread. The other possibility could be on the top end. Remove the valve cover and check the rocker arm lash. I'm not an expert here, but thinking in a logical manner leads me to checking these two items. Good luck.

 

[Torxhead]

Does sounds like the carb is running too rich. A quick check would be to check for deposits on a spark plug. Like if you pull a plug and its coated with black soot, the would indicate a over rich condition. Spark plug deposit charts are on the internet and repair manuals.

 

[Lumpy Grits]

:ww:

That's not VL.
You could have carb flooding issues.
CK your float level setting.
Also-Take your gas cap off the tank and see if there's any change.
Is the fuel filter's return line set at the 12 o'clock position?
Go back and ck you other work for good connections etc.

LG

 

[hdgapeach]

I'm with the rest of the guys (Torx, PB & Lumpy), backfiring with flames indicate you're losing spark or gettin' too rich to fire.

You can take the distributor cap off and turn the crankshaft back and forth some and get a good idea of how much slop you have in the timing chain. If the crank turns a good bit before the rotor button starts to move, you got a stretched one or wore out gear teeth troughs.

Try starting her up and let her idle till warm. Shake the under hood ignition wiring to see if she'll die. Found a bad splice in a ICM to coil wire before that was causing the same "dying for no reason" problem you're experiencing. Wires had slipped out of one side of a butt connector that was too small for the doubled up wires. When it was cool, it started an ran fine. As soon as it got warm, expansion would break the contact and she'd die.

Hey, it don't cost nothing to try! Good luck.

 

[Peanut Butter]

You can take the distributor cap off and turn the crankshaft back and forth some and get a good idea of how much slop you have in the timing chain. If the crank turns a good bit before the rotor button starts to move, you got a stretched one or wore out gear teeth troughs.

That's a cool idea! Never heard of that before.

 

[Lumpy Grits]

OP-Are you still with us?
LG

 

[hdgapeach]

That's a cool idea! Never heard of that before.

Actually picked that one up on my own. Got a '68 C10 with a 350 that was impossible to keep timed. Got so frustrated with it "wandering" I decided to pull the cap and turn the crank until I got everything pointed to TDC with the marks and button. That's when I noticed how much lag there was between the crank and the dizzy. Almost 1/8" of crank turn before the button thought about moving.

Pulled the cover off and the cam gear grooves were about 1/4" across the bottom and flat instead of u shaped. The tips of the teeth were sharp as tacks! Got my dollars' worth outta that gear.

 

[hdgapeach]

OP-Are you still with us?
LG

Oh NO! Another one M. I. A.