No idle...but why?

[Dubv1980]

Ok...
My 73 NADA Series III. Been running great, and suddenly it will not hold an idle without the choke pulled almost all the way out. I've adjusted the idle screw..to no avail. The truck runs great at speed, with the choke pushed in, but once the clutch is pushed down, the engine dies quickly. Any ideas...any vacuum hoses that aren't obvious? Its getting fuel, the fuel filter is new, all that jazz. Any ideas would be great.

Chris

[J!m]

Is it a Webber? Sometimes the ports get clogged with dirt, and you need to clear them. What's nice is, it's really easy!

1. rev the crap out of the engine with the goose neck off the carb
2. place your hand over the carb top when the engine is at top RPM and wait for the RPMs to die almost to a stall (but don't let it stall)
3. remove hand and keep it running with other hand on throttle
4. check idle...
5. repeat if needed.

When you are done, you may need to re-adjust the idle and idle mix (per carb. instructions) depending on how long it has been since you last adjusted it. If several 'cleanings' does not straighten it out, adjust the idle set and mix. If it still idles like crap, it may have to be rebuilt...

I have to do this occasionally in my series, and this trick always fixes it up.

I'm not sure if it will work with other carburettors...

[TeriAnn]

Use a Mity-Vac to check the diaphram for your brake booster and check the diaphram on the distributor. A vacuum leak is one thing that will cause this condition.

[a109]

As Jim suggests it is most likely to be a blocked idle jet in the carb. If the hand on carb method doesn't work a quick strip and clean of the carb is in order. The orifice is so small that the fuel filters won't stop the dirt that can clog the jet. When cleaning do not use metal probes to clear jets since most are brass.

John

[Dubv1980]

I tightened down a couple of the screws on the carb...tested all the vacuum areas...for whatever reason it seems to be fine now. I also ran some carb cleaner through it...maybe it was dirt, maybe it was the very slightly loose screw, either way, we're rolling fine now!
Thanks for the ideas-

Chris

[a109]

I tightened down a couple of the screws on the carb...tested all the vacuum areas...for whatever reason it seems to be fine now. I also ran some carb cleaner through it...maybe it was dirt, maybe it was the very slightly loose screw, either way, we're rolling fine now!
Thanks for the ideas-

Chris

For future reference squirting carb cleaner through a carb while the engine is running does absolutely nothing except remove a little carbon from the throttle area which isn't a problem anyway.
Carb cleaner is to help clean up a disassembled carb and is useful for that job.

Glad to hear that all is well again.
John