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MG Midget and Sprite Technical - 1275 help

Had fresh valve job and now compression is 135 130 130 125 front to rear. Before valve job front 3 plugs were clean and rear 1 was black. Put carb kits in. Same after valve job and still runs unsteady. Top of pistons and cylinders looked good. Did leak down with oil on top of pistons and all held. Can't figure out what's going on with the rear cylinder...
GF Greg Smith

couple of thoughts:

valve hanging up in the guide
valve lapped to the seat incompletely
bent valve

125 to 135 is only 7% (not ideal, but not totally NG either), are you sure that your uneven running is due to something to do with compression?

For instance, try swapping plugs around, or plug wires, to see if that black plug syndrome follows one of those. Also, could there be a bad post in your distributor cap?


hope this helps,
Norm
Norm Kerr

This thread was discussed on 16/06/2010

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