Carburator problem, I think

[JayChicago]

Today I tried to clear a blockage with high vacuum by choking at high RPM as suggested above. Didn't work on this carb. No change.

Needle valve does not appear to be the problem on this carb. I removed the front needle and seat, cleaned it, and put it back in. Fuel level, in both bowls, is right at the bottom of the inspection port, as supposed to be. No change, engine still dies when throttle gets down into the idle range.

I called Holley's tech line and described the symptoms. Tech said its not a common problem he hears every day. After a long time off the phone (researching, discussing, ??) and coming back on to ask more questions about the symptoms, the tech came back and said the only thing they can thing of is: something is blocking the idle circuit. He said do a rebuilt, and as best you can, blow out all the passages.

[37 Cab]

Be sure to check for vacuum leaks.

[JayChicago]

That sounds like a good idea. A vacuum leak should affect engine performance most during low throttle/high vacuum. But that brings up a question I have had. What's a good way to search for vacuum leaks?

I used to do it by spraying starting fluid around possible leak sources. But last couple times I did that on other cars I sprayed fluid directly into the air intake as a test of the test, and it did not increase RPM much, if anything slowed RPM. Is starting fluid not as volatile as it used to be? Corporate safety experts and lawyers dictating a change to the chemical formula?

I read someone suggest using an unlit propane torch. But that scares me a little, have not tried it.

[37 Cab]

I would not use starting fluid. Maybe brake clean.. Or propane. A quick check would be to partially choke the engine while idling and see if rpm increases.

[37 Cab]

Also could be a failed power valve if equipped but I`m sure the Holley tech went over that with you. Hard to say VIA internet.. Rich or lean? Do the idle adjustment screws make any difference? Are the plugs black? Notice any black smoke from tail pipe? Get back to us on partially choking engine and noting RPM change.. Good sign it is lean. Black plugs indicate rich.

[flatjack9]

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Originally Posted by philipswanson

In that case, it wouldn't run at higher speeds. Doesn't make sense either way. Suspect the idle circuit clogged. How about linkage sticking like a bad return spring.

Well, I guess I imagined this whole thing. Probably dreaming. Sorry.

[Charlie ny]

Jack knows...end of story. Been thru it myself !

Charlie ny

[flatjack9]

Thanks, Charlie.