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MG MGA - idle speed

I've got a problem with my '58 coupe. When I sit at idle the RPMs slowly decrease. If I don't keep my foot on the gas to give it help, the idle eventually goes so low that the engine dies.

Any suggestions as to what might cause this problem?

Also, the idle speed is higher with the clutch out than with the clutch in. Why might that be?

(crank has been checked. it's okay)
P.R. Fahey

You need to synch and adjust your carburetors. Refer to the manual. Double check your timing before you adjust the carbs.

I'd say you also might want to check your float bowls and fuel delivery, but if it's only a problem at idle then it's just an adjustment issue.

It is normal for revs to drop when engaging the clutch- this is caused by the added friction of the throwout bearing.

Mark J Michalak

Generally a too rich idle mixture will "load up" after a long idle like you describe. Properly set up carbs will usually cure this. Before addressing carbs check dwell and timing.
The Throw out bearing on a MGA is not a ball bearing like most modern cars. It is a carbon disk rubbing against a steel plate. See picture. To minimize wear on the TOB you should get in the habit of leaving the car in neutral with your foot off the clutch pedal while waiting at a light.
In the picture of the worn pieces you can see the off center wear pattern on the face of the carbon TOB and the heat damage to the face of the pressure plate. Revving the engine with the clutch depressed overheats and damages the 2 pieces.

R J Brown

Thanks for the responses. I appreciate the feedback and will have the carbs checked out. (I know nothing about them myself)
P.R. Fahey

If you buy the CSK 40 carb rebuild kits from Burlen, they come with a very clear step-by-step instruction sheet. The kits do not have new needles or piston springs (these differ with the specific application) but Burlen can supply the correct ones too. Tuning carbs with the gunson Carbalancer and Colourtune is really straightforward. Very satisfying and worthwhile job. AB
A Bennett

This thread was discussed between 11/12/2008 and 13/12/2008

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This thread is from the archive. The Live MG MGA BBS is active now.