Massillon Preacher

After putting on new carb after all my issues with old one even after rebuild, the truck starts right up but still won't idle to stay started, it will run smooth few seconds and then have a hesitation shake, "almost like an old dog shaking himself dry after a bath" LOL. It is just a second or so of this hesitation shake and then idle okay a few odd seconds ,then the hesitation shake again and after few times of this scenario it shuts off. I have tried the air fuel dialing and can't find any setting to stop this, so spots make it a little better or longer before it shut down or has the shakes but no answer there, don't think its setting of air fuel as the issue, what should I start checking from here?

84 Bubba T

Hi there, I would start by checking for vacuum leaks around the carb, or intake. Also try taking off, and plugging the vacuum hoses and ports coming from the carb to see if any of the hoses are bad.

Braggs

Need vehicle info please. Year, make, and model helps to identify the specific engine setup you have.

Massillon Preacher

It is 1971 Ford F100 with a 390 in it and the carb is a Holley 4160 4 barrel List 1850-1

1967 Tempest

I agree that there is most likely a vacuum leak. Also WHat is the idle set at? if it is below 500 then this might be normal. Might wanna try bumping it up to say 750 RPM's, to see if it smoothes out.

Is this an auto or manual? Not sure on Ford, but older GM cars/trucks used vacuum to downshift. So we are back to a vacuum leak.

One thing that gets overlooked is the power brake booster. If the one way valve is cracked or the seal is dry rotted etc, there is a HUGE vacuum leak.

Get a vacuum gauge. I can not tell you how many issues and just general tuning I have done with mine. It has paid for itself 1000x over. Buy it an put it on a full vacuum source.

Tell us the reading when you first start it...

http://shop.advanceautoparts.com/p/a...=actron+vacuum

The above link is to the one I have.

Massillon Preacher

After putting on vacuum Guage if I did it right got 15 to 20 reading bit it kept fluctuating and then shut down as usual.

88xlt

Have you adjusted the "idle SPEED screw"? that 1967 Tempest mentioned. It is on the linkage that the throttle control linkage hooks to.

Massillon Preacher

I will when I get home, off on Vacation right now but would idle cause it to seem idled ok for 5 seconds or so, then spuddering and idle bad a few seconds, then idle okay a few seconds and back and forth a few times before shut down?

burnthelight88

Are you feathering the gas and attempting to keep it alive while this is going on? Or are you just turning the key and letting it die?

If you're feathering the gas and its still dying then I'd say vacuum. 15 is a bit low, 18 is much better but that could be off due to the lack of carb tuning.

If you aren't feathering the gas then I'd say you might need to set the idle speed screw.