I have a 1985 D100 w/435 retrofitted to 1980 engine (no computer). 1945 Carb, Distributor with vacuum advance above throttle plate and an MP electronic ignition. No fancy performance upgrades.

It's been running fine, but suddenly started stumbling when accelerating in 3rd and 4th.

In 3rd, it stops stumbling around 30mph.
In 4th. it stops stumbling around 45 mph.

When it reaches 30 in 3rd or 45 in 3rd, it suddenly smooths out with a slight acceleration.

In 2nd on dirt road at low RPMs, runs normal.
After 45 in 4th on hgwy at high RPMs, runs normal.

Vacuum advance OK.
Disabled vacuum advance with no change

Broken/disconnected spring in distributor?

The springs are hidden under the pick-up plate, and the distributor is warrantied so I'd best not disassemble it.

Any suggestions appreciated.


Thanks,
DM

Do you have a different ECU you can swap onto the vehicle as a test?
DD

Also do you have a timing light?

What Is initial Timing in degrees with the vacuum advance disconnected, as well as total with the advance disconnected?

Greg

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D

17DEC21

Sorry for late reply. I Had to make a space for truck in heated garage. Fri AM 10F, Sat AM -5F!
Testing is tough! I'm 5 mi on a not well kept dirt road to reach pavement.

I'm a couple of years into geezerhood and starting to experience the associated deficiencies; memory, strength, etc. Please bear with me. A while back, I'd likely have repaired the issue w/o help, but when w/o 4WD in Montana, pride has no place.

Here's my observations:
Idles smoothly.
Runs in second gear no problem.
3rd and 4th balk or miss while accelerating.
3rd and 4th smooth out at about the same rpm.
Running on hwy above 45 has normal response.
Problem seems to be in same rpm range.
A thought! At higher speeds, I'm running on centrifugal advance; therefore, the springs are probably OK.
Still, it behaves like an ignition problem

Carb:
Accelerator pump - can see fuel flow from AP port.
Power Enrichment - I forgot to check. (see above)
Float at spec. 0.130 w/gasket (from MP repair manual).

Ignition:
Vacuum motor on distributor shows no leak. Forgot (see above) to check for stuck or disconnected.
Since it runs fine at low and high rpm, I assumed (see above) both plugs and wires OK.

Today's (maybe tomorrow's) Tasks:
Check Timing with Vacuum advance and compare to timing w/o vacuum advance.

If no problem with VA, then replace MP ignition module .... maybe change anyway.


Thanks for the responses;they're really appreciated. They help me think.

DM

D

I understand the OP concern... I dont know if this situation can apply to a Holley 1945 but...

When I bought my 69, it had a "kick" (stumble) while doing low-mid RPMs (not sure how many, in second gear maybe between at 20 to 30 MPH?, it was 8 years ago...). The previous owner told me that problem was starting to occur (so it was "new", I should believe). Carb in car was a Holley 1920. No problem after reaching some higher RPMs. I had to slip the clutch until reaching some speed and then fully release (not fun for the clutch) to go.

Tried cleaning and fiddling, then I replaced the carb with a NOS 1920. I never had that problem again.

I remember reading discussion about passages blocking with time with new gas with alcohol, not knowing what abuse the carb went through, worn shafts, etc...

I will recommend the OP to check carb jet too (obstruction?), But one option maybe (if he can/want) is looking for a carb replacement (temporal to test, or definitive). The best ones are NOS, but they go for an arm and an leg. Big store carbs are a crapshoot, some small store might be more careful servicing/rebuilding them.

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18DEC21

Here's the dope so far:

Timing:
Idle 750 rpm approx
w/vacuum 16 deg
w/o vacuum 16 deg

1100 rpm approx
w/vacuum 20 deg
w/o vacuum 16 deg

At 1100+ rpm approx engine picks up speed
without using accelerator.
Vacuum maxes out.



MP Elec Ign
I'll do that tonight and report tomorrow.

18DEC21

To: DusterIdiot

Tach? Tach? This a 1985 Dodge Truck! It's functional only - no fancy amenities.

I had a tachometer once. I lent it to somebody. I can't remember who, and it seems who has forgotten where he got a Tach. I've been meaning to replace it.

I haven't changed my driving habits; the truck has changed.
Your quote from my explanation is meant to indicate that the malfunction may be related to rpm. I hoped that an approximate rpm could be inferred from the speed when an event occurred. You are absolutely correct though, knowing the rpm would be a plus.

I appreciate your input. Thanks,
DM

D

The weather here has been a bit nasty temperaturewise, and I am still preoccupied keeping the firewood supply current. Tonight, it'll go down to -13F, and tomorrow night it's to descend to -23F. The coolies below me are usually 10-15 degrees colder!

when this failure began, I had checked the ignition system rotor, cap, all wires, and plugs. All checked OK except the plugs needed to be regapped. I didn't have any spares. The problem persisted.

We did have a couple of warmish days during which in frustration I went back to square one. I had bought a set of plugs and this time replaced them.

Success!

I want to thank everyone who responded for their time and suggestions. I'm embarrassed to have troubled you. I really think that time has finally taken it's toll on my ability to process information orderly.
Thanks again,

DM

Thanks for posting the fix. We all learn from your efforts.

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