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MG MGA - idle problems

Idle drops off sometimes and getting worse as the days pass. Have taken the SU tops off and all is clean. Oil levels are fine. air filters are clean. Choke pull is set so 1/2 pull increases idle without actually engaging the choke and I can pull it slightly to prevent the stalling but then most of the time the idle is way too high. I stand looking at the carbs as it idles fine, move the throttle and sometimes it continues to idle fine, sometimes it drops off. Sprayed around the throttle shafts with starting fluid and WD 40, neither made a difference. Suggestions appreciated.
RAP Palsgrove

Check your mixture--you may be running too rich.
R. L Carleen

Spray around all the joints on the intake manifold, check your vacuum lines also, you may have an air leak. If it is running rich as suggested above, you may have a dirty/sticky float valve or excessive fuel pump pressure.
John H

Pulled the plugs and they are a grey tan on all 4. Best to spray with what?
RAP Palsgrove

Spray using your WD 40 or starting fluid at carb to manifold joints, manifold to engine, etc., anywhere air could be leaking in. The color of your plugs appears to be correct, which would reduce the chance that you are running rich. A very small air leak can have quite an effect at idle but won't effect drivability. One more thing to check is the mechanical and vacuum advance in the distributor, if the mechanical advance is sticking in the advanced position it will increase idle speed. Remove the cap and rotate the rotor counter clockwise until it stops by hand, when released it should spring back smoothly. If it doesn't, clean and lube the mechanical advance.
John H

If your carb jets are worn "bell mouthed" at the top of the jet, common on really old cars with "original" or long used carbs, the idle speed can run too rich and speed can drop off. Since this "bell mouthed" jet has little effect above idle speed, spark plug coloration can be "normal"! If you adjust the jets for a "perfect idle" with this condition, it runs too lean above idle.
OLD BILL-67

Next time let it die then pull the plugs. If you have a float issue, that pair of plugs will be wet.

What you describe is relatively normal, even on "good" cars. The siamesed intakes, low signal at the jet, and poor chamber turbulence add up to erratic idle. In fact, most tuning books suggest you "clear the carbs" occasionally to keep things running.

With modern fuels, plugs read a bit "leaner." Brown is too rich. If dizzy wear has stolen some of your advance, you will lose idle quality. Late ignition is smoother.

Good luck,
Bill
Bill Eastman

This thread was discussed between 02/11/2005 and 10/11/2005

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