My 360 dies at idle

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Bill Crowell

Bill Crowell

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It's a factory stock 360 with a ThermoQuad that was running well until the other day, when it started dying at idle. It will idle OK for about a minute when you first start it up, but then it starts slowing down and eventually dies.

In the past, when this engine would start running badly, I would replace the distributor cap and rotor and that would always correct it. I tried that this time, but no go.

It runs well under the carb primary circuit, when you give it some gas. It sure is acting like it's running out of fuel at idle, though, but I'm not sure. The idle quality, while it does idle, is rather poor. But how can it really be running out of fuel if it runs well on the primary circuit of the TQ?

Suggestions for what to check? I guess I should start by replacing the fuel filter, but I'll bet it is OK.

If it were a plugged idle circuit, why does it idle OK at first, and then slow down and die?

Do you think I should pull the idle adjustment screws out of the TQ and shoot some carb cleaner into the holes?

Thanks a lot, guys.
 
Try reving the engine while its reving close the choke plate till it almost stalls try this several times if there’s a chunk or dirt this will usually pull it through.
 
When engine is cold the choke closes and pulls into place the fast idle cam. When you start the engine, the choke is pulled slightly open by a small diaphragm and the engine runs on the fast idle cam. When the engine warms, the choke is fully open and the fast idle cam swings out of the way to curb idle. It sounds like the choke is not working (or working poorly) and is coming off the fast idle cam much too soon.
 
I chased this problem on my C10 with 350 build - checked vacuum - timing - rebuilt carb - checked fuel line - pump - pressure regulator all with the same result "nothing" changed the POS - TSP new distributor for a new Summit brand problem solved
 
I would like to thank all of you nice people who replied for trying to help me, and to assure you that I did try everything you suggested, to no avail. So I had to take the vehicle to a hotshot mechanic friend of mine, who is one of the last mechanics in my area who still works on carbureted engines. When he figures out what the problem is, I'll be sure to post a follow-up to let you know what it was. Thanks again
 
You can also clean the idle circuits by counting how many turns out the idle screws are, then removing them and squirting carb cleaner (with a straw) in the holes. Might also possibly have a stuck float...
 
It turned out to be that the ThermoQuad was leaking fuel from the float bowl into the engine, partially hydro-locking it, and then the gas went into the crankcase. It still ran fairly well on the primary and secondary circuits of the TQ, and the idling problem was the main symptom once it was running. Another clue was that my oil pressure dropped from its normal ~50 lbs. to only 15 lbs.
 
Whoa... that is a lot of thinning. Hope it is all OK.

My '62's /6 had a chronic carb leak and the PO did not know. When I 1st changed oil, it came out like water. Bore wear was pretty bad but that problem was going on gradually over many years, a little at a time over a few k miles.

Once you run it a bit more, I'd take compression readings on all cylinders.... just in case.
 
MOPEkidD-3 said:
You can also clean the idle circuits by counting how many turns out the idle screws are, then removing them and squirting carb cleaner (with a straw) in the holes. Might also possibly have a stuck float...
Click to expand...


When my 340 did things like that I knew that the thermoquad plastic bowl was warped from the motor heat and allowing fuel to dump in randomly. After 36yrs and three of those I went to a carter performer series. Now I'm a 392 gen3 so no worries anymore.
 
Yes, Peter, I know that TQs can be a PIA sometimes, and maybe I am a glutton for punishment, but I really like them. So is the Carter Performer carb square bore or spread bore? Gotta have spread bore!
 
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