Irratic tickover

I have a 1979 MGB GT and am having a problem controlling the tickover speed. If I tweek the throttle to rase the RPMs and then take my foot of the throttle the engine takes some time to return to the tickover speed of 800rpms. On occations the revs stay high (and sometimes rise further) for no apparent reason. The carbs (HIF)and pots have been cleaned well. Any help appreciated.

Reply to
MJN
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I have the same problem - although I'm no mechanic (I never got my hands dirty until about a year ago) I'd read this was down to valve seat recession caused by not having an unleaded head.

Carl.

Reply to
Carl Woffenden

Carby's leaking air. Make sure the return springs are in place so that the butterfly's close to the stops. The carbys could also be worn.

Had a tune up lately? were the carbys checked and tuned?

Not valves - this can be checked by adjusting the clearance.

Reply to
Rob

The carbs have been cleaned and checked. The return springs are OK. Could it be the small valve on the butterfly that is causing the problem (I think I read somewhere)?

Reply to
MJN

Those valves are for pollution control and usually cause the motor to run on.

But this problem still comes back to air leaks.

You could change the butterfly's or solder them closed.

rm

Reply to
Rob

Check for air leaking past the butterfly spindle -

When engine is idling fast, drip a few drops of engine oil on the shafts where they come out of the carb body. If engine slows down when this is done you have found the problem

Moss Motors have repair kits.

Ian f

Reply to
Liz and Ian

I would take that with a grain of salt, Carl. I would suspect that the throttle cable might be sticking due to a damaged strand in the inner cable -or- possibly worn carb body where the throttle spindle goes through it, allowing an air leak under just the right circumstances, along with possibly a slightly rich mixture.

I have not seen any recession on any of my cars and none of them have unleaded heads. A quick test would be to check the clearances; if there has been recession, the clearances would be closing up, which could cause the valves to eventually burn out when there is no longer an adequate clearance.

-Rock

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Reply to
Rocky Frisco

I found an air leak in one of the carbs (following a rebuild).

Thanks,

Carl.

Reply to
Carl Woffenden

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