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MG MGB Technical - 77b w/miss


Miss, miss and more miss........

Had a serious carburetor problem, but I think I got that sorted out. (thank you!) Shortly afterward I developed an electrical problem. Died on the freeway, no power.

The indicator lights been flickering since I got the car about 6-7 months ago, through my research I found that meant the brushes on the alternator were worn.

Replaced the alternator and battery, afterward I noticed a miss after fully warmed. The longer I run it the more misses develop, it did die on me twice and I can't seam to make it happen again. I was able to discern that when it dies, the positive side of the coil has no voltage.

The next day after the power was back up I disconnected the ignition lead (positive side of the coil) and ran a direct line from the fuse box. Thinking that this would eliminate a faulty ignition switch or relay. If no miss, I should be looking in that direction. But the miss still happened...

I replaced the cap, rotor and plugs about 1k ago, and replaced the coil today. The P/O installed a pertronix pick up, I'm guessing max 2yrs??? Not sure of the air gap adjustment? I set it to factory spec. .010 - .017 (mines at .015) then reset the timing. The miss still persists...

Is there and reading I can take on the cables? Ohms?
To determine if there pass/fail. Also could the Pertronix be bad already, somewhere I read about 10yr expected life span?? Is there a test for this? I do know it's solid state.

Any other ideas?

Thank you,

kb.



Kevin Boldin

Kevin,

The only things you haven't changed yet is the Pertronix unit and the HT leads. Fit a set of points to eliminate this unit and make up another set of leads preferably copper cored.

I'm not 100% sure that this is an ignition fault I know it sounds like it but you haven't said whether it only occurs when the engine is on heavy load, at high revs or just what brings the miss on. Have you tried applying a little choke when the miss occurs to see if this mixture adjustmnent eliminates the problem (I hope your car doesn't have auto choke) The miss could be caused by mixture weakness and you must check the induction side for leaks. I assume that the needle/jet are known to be correct.
Iain MacKintosh

Mostly it's at idle up to about 2k rpm and I have an auto choke. Thought I was pretty close on the set up with the carb, I'll go back through it again.

I have the 45de distributor, no lobs, how would I go about setting up the points configuration? Also, I read on the board about valve adj, my book says warm but reading a thread they referred to cold, do you adjust when warm or cold? I adjusted them warm, not at operating temp.

Being a rookie, I probably have it mucked up!

kb.
Kevin Boldin

What about a vacuum leak? What kind of miss???? I had a terrible time tracing a vac leak at the carb base on my weber setup.
P J KELLY

This thread was discussed on 28/01/2004

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