My 71 (F100, 302, Holley 2BBL) has started skipping at a certain throttle position... anything beyond barely cracked to about half throttle.

Not sure if skipping is the right word, it basically seems to die, then restart, die, restart, etc very quickly causing the truck to jerk like crazy.

Seems worse the colder it is.

Any ideas?


Tom

 

You would think that these holley 2bbl's are junk from reading of all the problems you guys are having! I just crank mine up and drive!

Keep in mind that I am no mechanic, but the only thing I can think of would be a busted power valve that floods the motor and then burns it off, then floods again. My second solution, is a clogged jet or metering rod. A peice of trash blocking fuel, and after part throttle, the power valve provides enough fuel to make it run.
Thats all I can think of for now, but dont attack the carb until you rule everything else out such as vacuume leaks and proper timing. To check for a vacuume leak, spray some carb cleaner along your intake to head gasket and at the base of the carb. If the RPMs change, you have found your leak.

 

Finally got around to popping the breather off tonight, gas everywhere.

Saw kit prices from $10-$30, thinking about just buying a carb and bolting it on.

AZ has a Champion for $149, a TOMCO for $149, and a Holley for $109. Any recommendations?

All are model 2100.


Tom

PS: Not sure if this is going to link to the post I replied to since I changed the subject... just in case it's a 302 automatic.

 

Ordered a Motorcraft 2100 but it didn't fix it!

Checked for vacuum leaks, loose plugs, and the timing.

When idling or with the throttle *barely* cracked - everything's okay. The slightest bit more and it dies completely, a little more and it picks up but is shuddering, 3/4s to full throttle seems okay.

The fuel pump is fairly new... I was thinking a fuel pump problem would show up more at higher RPMs anyway?

Any other ideas would be appreciated.


Tom

 

I'm shotgunning! Just replaced the fuel filter... same thing.

Need suggestions!

 

Disconnect and plug the vacuum line to the vacuum advance on the distributor and see what that does.

 

Sweet! That eliminates the symptoms...

So does that mean it's advancing too far? Or the diaphram is bad causing a leak? I have it hooked to the carb vacuum port so the fact that it idles okay makes sense now.

 

This sounds like one of two things, now that you found it ran smoother with the vac. plugged and disconnected.

(1) The advance was connected to the wrong vac. source at the carb.
My Edelbrock has two sources on it. One that is ported and one that is constant vac.
I found that the constant source caused the same results you had. Hence I'm running the ported source as was the recommended set up in the manual in the first place. I had tried the other port out of curiosity.

(2) Your distributor advance is failing, the diaphram or the internal mechanical parts are not working correctly.

Hawkeye

 

I think we can rule out #1 because it just started doing it out of the blue, if it was the wrong source it would've done it all along, and I think there's only one port on the Motorcraft.

But, if yours was doing the same sort of thing on constant vacuum that could point to too much vacuum.

Guess I just need to know if the advance module is the most likely candidate or some of the distributor internals.

BB, it was your idea to try plugging the advance... what did you have in mind?

 

Ok sounds like you got it isolated, now we have to root cause it. First thing is to verify the point gap is to spec. Then check the ground strap on the breaker plate for loose wires or connections. Next, hook up a vacuum hose to the vacuum advance and suck on the hose while watching the breaker plate rotate, it should be a smooth action with no slop or play. My experience is it will take a lot of sucking to get the darn thing to start moving. A hand vacuum pump will work a lot better if you got one. You will know right away if the diaphragm is ruptured and needs replacing. Let us know wht you find out and we'll go from there.

 

I had the same thing on my '69. On mine, it was the Pertronix that I installed. One of the wires routed by the breaker plate and it had rubbed a hole in the insulation. When the vacuum advance moved the breaker plate, it rubbed up against the bare wire and shorted out the Pertronix. I rerouted the wires and taped up the bare spot.

If you are still running points, then I suspect the bushings in your distributor are shot and this allows the breaker plate to **** sideways when the vacuum advance moves it. This changes the point gap. When the motor starts to die, it loses vacuum and goes back to the original spot, the point gap is restored, the engine picks up, vacuum is returned, and the whole things starts over again. A rebuilt distributor is probably your quickest and cheapest (in the long run) option here.

Hope that helps.