Spitfire & GT6 Forum

Idle Speed

Moss Motors
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cwm3232 Colin M
Boston, MA, USA   USA
Hey guys! I have a 1980 Spit and I recently noticed that my idle speed has gone up by about 200-300 rpm without obvious cause. The choke isn't on and I haven't changed the idle speed screw. I am planning on just loosening that idle speed screw to bring it back down to normal levels ~900-1000 (my spit doesn't do well idling much below 900- not positive why but that seems like a good next project!) Has anybody else had their idle speed randomly increase like this? Any suggestions?

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SpiTazz72 Avatar
SpiTazz72 Bryan H
Magnolia, TX, USA   USA
Does the idle change after you drive it? There should be a spring around the idle screw to keep it in place but if the spring is missing I've seen the screw actually go in (Faster idle) once the pressure is off it from the linkage.
You might have an inlet leak. Do you hear a whistling sound? It could be any number of gaskets, hoses or connections on the suction side.

carChips Avatar
carChips Victor Harnish
Kelowna, BC, Canada   CAN
1933 MG Magnette
1973 Triumph Spitfire 1500 "Chip"
1989 GMC Sierra 1500 "Bush Truck"
Check the end of the choke cable and see if it's loose at the carb. The choke my not be fully off.

'S all for now

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poulsbobill Bill K
Poulsbo, WA, USA   USA
If you have played with the choke screw and not adjusted correctly it will move up the idle if screwed down too far. Also the bypass valve may be getting old and letting air in at idle.


1980 Spitfire

Edited 1 time(s). Last edit at 2017-11-09 07:38 PM by poulsbobill.

Doug in Vegas Avatar
Doug in Vegas Douglas D
Las Vegas, NV, USA   USA
If you have a single Zenith Stromberg. - First things first: While the car is at idle grab the intake manifold and give it a lift and see if your idle changes.

If so, the gasket has failed and you have multiple vacuum leaks.

This is usually due to the two bottom studs being loose so you can sometimes luck out with a good gasket and lock those down but the silver gasket will likely be toast.

Outfect Avatar
Outfect Dave B
La Sal, UT, USA   USA
1940 Ford N Series Tractors "Henry"
1951 Other Not Listed "SnowMan"
1979 Triumph Spitfire 1500 "White October"
1980 Triumph Spitfire 1500 "Tangerine Dream"

Simple check. Can you slow the idle by pressing on the throttle lever at the carb. If so you have a weak return spring. Otherwise check for vacuum leaks at the manifold or piping like Doug suggested.


Edited 1 time(s). Last edit at 2017-11-10 01:07 PM by Outfect.

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