Sticky high idle speed

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ChickenPinz
United States of America
Posts: 327
Joined: Tue Feb 11, 2020 7:16 pm

Sticky high idle speed

Post by ChickenPinz »

Coming down to idle slowly (as in normal driving), the idle settles at around 1080-1100. If I tap the accelerator pedal and let it snap back, it'll drop down to about 970-1000 which feels more correct. Pulling the linkage by hand near the carbs won't bring the idle down. I'm looking for ideas on where to look.


Test is with a warmed up engine.

Carbs were rebuilt by JimL a bit under 3y ago, and are tightly secured. Main jets are 130 (were 125). Air filter is clean. Fuel pump is new. Fuel hoses are new.

Cross-over hose was just replaced, brake-cylinder holds vacuum without leakdown (tested at 5inHg).

Ignition is Pertonix with original cap & wires (not civilian). Timing was set by Andre and me two years ago, and IIRC is set at 8mm. Might have the Unimog spark plugs in it.

Valves are adjusted correctly.

Exhaust system is good.

Thoughts on where to look next?
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ChickenPinz
United States of America
Posts: 327
Joined: Tue Feb 11, 2020 7:16 pm

Re: Sticky high idle speed

Post by ChickenPinz »

So....adjusted the timing to be about 2-3mm advance when cold, and no improvement.

I don't think it's a mechanical thing because when it idles high after coming to a stop, it'll idle down correctly if pulled down by letting out the clutch a bit and releasing it.

It now has the correct Pinz spark plugs, and correct timing, but still not dropping to the right idle after it's warmed up.


Next debug step is reverse-sniffing for vacuum leaks using an unlit propane torch.

Open to other ideas.
timing1.JPG
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Jim LaGuardia
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Location: San Bernardino Ca
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Re: Sticky high idle speed

Post by Jim LaGuardia »

Lube the pivot pin on valve cover and check for worn plastic link ends.
Feel free to call, I prefer talking to texting.
Cheers, Jim LaGuardia
http://smg.photobucket.com/albums/v510/Goatwerks/
"Arch Magus of Machines."
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