Engine stumble

69SKCharger · May 29, 2018

Not sure where this belongs, could be fuel or electrical, but I have a stumble that stalls the car. It's a 383 HP. Stock with exception of a RV type cam and edelbrock 650 AVS carb. It has an old accel electronic ignition box and distributor.

The problem is that during normal acceleration the car will stumble as though fuel starved or spark is shut down. Its actually kind of violent with the std transmission. Usually it restarts itself, but has completely died on me with difficulty restarting. Its not consistent but random.

I have cleaned the carb, reset the floats, set the idle air mixture and checked timing. The fuel filter and pump are new, as is the tank and pick up.

After all that, I still had the stumbling, after driving for a while, it seemed to go away, but suspect that's temporary . Looking for suggestions on what to try next.

threewood · May 30, 2018

Buy a fuel pressure gauge, tee into the rubber line and tape the gauge to the windshield and drive around. You will see if you have fuel delivery issues at wot. If it drops to zero when getting on it there is an issue. Seems the fuel pump rod is a possible issue as well as it can wear down and not actuate the fuel pump arm completely.

scot · May 30, 2018

What exactly do you mean by "Usually restarts itself" ? You don't have to crank it or it you do ? Sounds like an ignition problem to me. I'd be looking at that Accel ignition box and maybe the distributor. Is it a points or electronic dizzy ?

mtbase · May 30, 2018

threewood said:
Buy a fuel pressure gauge, tee into the rubber line and tape the gauge to the windshield and drive around. You will see if you have fuel delivery issues at wot. If it drops to zero when getting on it there is an issue. Seems the fuel pump rod is a possible issue as well as it can wear down and not actuate the fuel pump arm completely.

Agreed
Could be a worn down fuel pump rod, perhaps a weak fuel pump, or a dented fuel line causing a restriction. The fuel pressure gauge will, at least, prove/disprove this and is minimally invasive.

Is your gas cap vented? Just a thought

69SKCharger · May 30, 2018

By restart I mean it stalls, but with the std transmission the wheels turn the motor over before I get to depress the clutch and it starts back up.

The ignition is electronic, and its probably 40 years old, so may be the culprit, but also would think it either works out doesn't.

I can check fuel pressure. Maybe it's the rod. But the strange thing is that's its not under WOT, it happens under normal acceleration. Thinking back, last year it would only happen when cornering and accelerating, not now it's in a straight line.

The fuel cap should be vented, and the filter neck also has a breather tube.

69 GTX · May 30, 2018

Check your dist. cap wires, & coil. Also if it's a vacumn advance, make sure the advance is working. Also recheck your timing. Sometimes the coil will build up heat and lose some of it's voltage making it weak.

Ranger16 · May 30, 2018

69SKCharger said:
The ignition is electronic, and its probably 40 years old, so may be the culprit, but also would think it either works out doesn't.

Not necessarily, I can't speak for your type, but my Mopar Performance ignition had stalled on me a few times when I first got the car, but usually would restart. Long story short, it turned out to be an overcharging regulator that fried the ECU. I replaced both and it has been problem free ever since. Just something to consider.

oldbee · May 30, 2018

Awfully small wires feeding out of that electric box && 40yrs.?

727 · May 30, 2018

Check your ground connections

oldbee · May 30, 2018

My Accel BEI & yellow Super coil died after 30yrs. First couple starts we’re fine & then nothing; probably 20K miles on it.

AR67GTX · May 30, 2018

My 440/Edelbrock combination didn't stall as badly as your description but I would get a big stumble when I opened the throttle. I finally traced it to the accelerator pump well in the carb body. The Edelbrock specs for setting the accelerator pump height were too short for my carb and the accelerator pump rubber was positioned below the bottom of the notch in the pump well that allowed gas in from the fuel bowl. So every time I opened the throttle I got a shot of virtually nothing out of the shooters. I had to bend the linkage and put the pin in the inside hole to raise the accelerator pump rubber up enough to just barely above the bottom of the notch. This put the measurement to the top of the accelerator pump shaft considerably greater than Edelbrock's rebuild instructions. And all of this was with a brand new, correct part number Edelbrock accelerator pump unit. After this the engine responds strongly from a stop when I mat the accelerator.

Kind of a long shot but might be worth checking.

69SKCharger · May 31, 2018

Actually, AR67GTX, that is worth checking. I also get a stubble (very slight) when opening the secondaries on the carb, and maybe that's the culprit. Work a try for the effort involved.

Went for another drive last night, no symptom of any problems mentioned above. This is the type of trouble that is so frustrating. I'll start putting parts together for a new EI, check my grounds and fuel pressure, meanwhile hope that it just doesn't happen anymore.

threewood · May 31, 2018

69SKCharger said:
Actually, AR67GTX, that is worth checking. I also get a stubble (very slight) when opening the secondaries on the carb, and maybe that's the culprit. Work a try for the effort involved.

Went for another drive last night, no symptom of any problems mentioned above. This is the type of trouble that is so frustrating. I'll start putting parts together for a new EI, check my grounds and fuel pressure, meanwhile hope that it just doesn't happen anymore.

Last summer I went through the same issues which is why I suggested the pressure gauge in the fuel line. During the day, pressure would drop to zero and motor would cut out but at night it would only drop to 2 psi or so so it kept running. Weird problem to be sure. Good luck.

Engine stumble

69SKCharger

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threewood

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scot

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mtbase

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69SKCharger

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69 GTX

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Ranger16

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oldbee

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727

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AR67GTX

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threewood

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