Adjusting carb but cannot get idle

1) Did you drive the car a couple miles to warm up first? 2) Year of car? Is it bone stock, orig vac advance? 3) 30PICT or 34PICT? 4) Is the throttle plate fully closing at idle?

Often, idle problems are caused by dirt particles in the tiny idle fuel passages. After it drops to 500 RPM, try very slowly opening the throttle by hand. Is there a smooth transition to higher RPMS, or is there a "dead" zone or even a drop-off in RPM? That could give a clue.

Normally, I wouldn't implicate it, but is the manifold heat working?

When the RPM drops off, is it possible a couple cyls aren't firing? Pull each plug lead off and see if there is an equal effect.

This kind of problem isn't easy to trace; you need all the input you can get in symptoms.

Speedy Jim

Thanks Jim. The manifold heater is working. That was were i first started trying to solve my problem. The car is a stock 74. My next step is to remove the carb & rebuild it. I believe that a circuit must be clogged.

With the choke active until warm-up it idles well & maintains a stedy rpm. Once the choke is fully open It idles in slow osculating pattern of rpm's over say a minute or two until it slows to a stall. The adjusting screws of the carb (big screw) seems not to effect the rpm's

Temp fix - if you need on a daily driver.

Ajust the choke so it doesn't completely open.

You will get about 1 minute driving between cold and warm where it doesn't want to idle, then it will run fast, off throttle, but it will be drivable till you sort it properly.

Rich

LOL The "osculating" pattern does suggest clogging. You need hi-pressure compressed air and total disassembly. A good soak in solvent helps too. Don't be too disappointed if it doesn't solve the problem on the first (or second) try...

Jim

Unscrew the idle jet located over the alternator on the side of the carb. Use a tiny tiny wire to clean out that debris clogging the jet. Sometimes compressed air does not clean it out. When you rebuild the carb you will still be cleaning out this jet among others.

You also need to make sure that the electromagnetic cut-off valve is working. This in the one close to the throttle arm and has the wire going to it. Turn on the ign, don't start the engine, and unplug and replug the wire. You should hear a click each time. Sometimes these valves loosen some so you need to make sure that it is tight to the body of the carb.

later, dave (>

Thanks guys ! After all the heat riser cleaning & carb rebuilding my problem turned out to be a vaccum leak. The hose that goes from the intake manifold to the air cleaner was causing all my problems. I plugged it up at the manifold & i'm off & running. Why it was never a problem until recently is what i do not understand!