Full throttle issues

Full throttle issues
G

grunt

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Location
Connecticut
Vehicle(s)
1979 CJ 304, 400 automatic
My 1979 CJ AMC 304 with a GM Turbo 400 and mc2100 carb idles fines and drives great until I punch it to wide open throttle (WOT). It just dies and at times shuts off. If I roll the throttle slowly in drive to WOT it is fine. If I have it in parked, it revs fine even from a idle to WOT. What gives? I messed with the timing and it is fine. Any ideas would be appreciated.
 
First guess would be the carb accelerator pump is out of adjustment. Another possibility would be an out of adjustment float not being able to fill up the float bowl.
 
If all else is ok, then the carb would be the best guess. It sounds like it is starving for fuel. Check fuel pressure, float level, accelerator pump, etc. I wouldn't expect it to shut off completely though. Mine used to have a terrible bog off idle until I resolved the jets and power valve settings.

It may be something in the timing such as mechanical or vacuum advance problems.

It works better parked because there is no load on the engine.
 
^^What they said ^^
 
Ok thanks.....due to my work schedule I'll be checking this out this weekend and will post my results soon after...
 
I checked my vacuum advance by using a timing light. At idle it was steady and with the engine reved the timing mark moved considerably. So I assumed that my advance is fine. My accelerator pump rod is in the third hole from the bottom and the other end is in the hole closest to the accelerator pump. I believe this correct for the AMC 304 engine. Also this is the original carb to the motor which has 56,000 miles. Now that I ruled out my advance do I need to bring the float up for more fuel? 7/16 of a inch sounds right to the tip of the float to the top of the bowl? Appreciate all the info....
 
to check the vac. advance pull the vac. line at idle and see if the timing changes. By just reving it up you could be seeing the mech. advance change.
Look in the carb and move the throttle to see if the acc. pump is squirting gas.
 
Old Dog said:
to check the vac. advance pull the vac. line at idle and see if the timing changes. By just reving it up you could be seeing the mech. advance change.
Look in the carb and move the throttle to see if the acc. pump is squirting gas.
Click to expand...

Ok..pulled the vac. line at idle and looked like it didn't change....carb is squirting gas....so?.....
 
I wasn't thinking to clear yesterday when I wrote that.
If you have the dist. hooked to ported vac. it might not change. You will have to disconct the vac. line from the carb and suck on the end to see if it changes.
I run full manifold vac. on mine so it does change.
What do you have your timing set at?
 
Two questions:

When it dies, does it sputter/cut out or just act like someone shut the key off?

Can you describe a scenario when this happens; like are you cruising on the along and then you floor it, rpms start to climb and it dies or you are at a stoplight and floor it and it dies, etc.....curious about the rpm this is happening at.
 
Old Dog said:
I wasn't thinking to clear yesterday when I wrote that.
If you have the dist. hooked to ported vac. it might not change. You will have to disconct the vac. line from the carb and suck on the end to see if it changes.
I run full manifold vac. on mine so it does change.
What do you have your timing set at?
Click to expand...

Looks to be around 5 degree BTDC...
 
jasonmark1993 said:
Two questions:

When it dies, does it sputter/cut out or just act like someone shut the key off?

Can you describe a scenario when this happens; like are you cruising on the along and then you floor it, rpms start to climb and it dies or you are at a stoplight and floor it and it dies, etc.....curious about the rpm this is happening at.
Click to expand...

Say at a stoplight and floor it and it dies and cruising and floor it dies...rpms don't climb...acts like someone shut the key off...
 
Huh...well if it feels like someone shut the key off...thats one thing.

In my experience a fuel problem on a carb'd vehicle won't just shut down like that; not when you can run it to full throttle if you go slow.

You said you do have a good shot of fuel when you snap the throttle?
 
Does it ever backfire when you floor it.
 
jasonmark1993 said:
Huh...well if it feels like someone shut the key off...thats one thing.

In my experience a fuel problem on a carb'd vehicle won't just shut down like that; not when you can run it to full throttle if you go slow.

You said you do have a good shot of fuel when you snap the throttle?
Click to expand...

Doesn't shut off when you roll the throttle.....nearly every time if you peg it.....definitely good shot of fuel......
 
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