help, rough idle 302

[rd100]

I've got 302. The engine belt was squeeeling badly two weeks ago so I hadn't started it up in that amount of time until I got a replacement and put it on. This was my grandfathers truck and I'm just now getting into seeing what I need to do with it. Previously it seemed to have a hesitation or stumble as it revved but it would always idle fine once it was warmed up.

When I went to move the truck it had a hard time starting and wanted to die at idle but the engine was still pretty much cold as I only moved it about 30 feet. I replaced the belt and cranked up the engine. It just wouldn't hold an idle and kept shutting off.

I also got new spark plugs and wires when I got a belt and went ahead and gaped and replaced the plugs and wires. Still ran the same.

I adjusted the idle screw on the carb which of course did help it hold an idle, but it's a pretty rough idle.

I sprayed in some carb cleaner and cranked it up and it seemed ever so slightly better. It seemed to sort of cycle where once in a while it would actually idle smoothly for like 8 firings of cylinders and then back to rough for a bit.

Does this sound like I need to clean the carb as the next step?

If you rev the engine it sort of stumbles as it revs up. You can hold a high rev and it's pretty smooth, if you let off during the wind down it makes some rough noises.

[fordman]

cleaning or rebuildign the carb sounds right or it could be a vacuum leak. spray the carb cleaner around the base of the carb and the vacuum lines and see if the engine runs different when you spray a certain spot.

[papabug71]

Dist. cap & rotor? Points? Condenser?

Is the coil leaking or look does it look melted?

[Banjo]

be sure choke is fully releasing and make sure carb hold down bolts are tight. Leave it running a long time in one spot and see if it changes. If your choke is fully released, the upper butterfly will be straight up and down or very close. If that butterfly (plate) isn't open real far, your choke is staying on. They will run very rough with choke on. Vacuum leak will cause rough running too and usually caused by carb loose on intake or vacuum ports in carb (or intake manifold) have been knocked off. Harbor Freight sells a vacuum gauge for around $15-20 that is invaluable in diagnosis, wish I'd known how valuable vaccuum gauge was when I was younger. If vacuum gauge isn't dead steady, you've got a vacuum leak and must find/fix, which can sometimes be found as fordman mentioned spraying carb cleaner around wherever gaskets are (base of carb, intake, ) to see if idle speed picks up/races temporarily. If it does, you've found where your vacuum leak is coming from. they won't run smooth w/vacuum leak or choke not fully disengaging. Banjo.