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MG MGB Technical - Studders above 60 mph

This weekend at the start of a 300 endurance run my B started to occassionly miss aboe 60 mph. If I backed off the throttle for a bit or slowed down below 55 she would run fine. The week prior I had tuned the carbs, think I may have gotten them a bit to lean as my mpg went up 3-4 miles per gallon. Replaced the fuel filter, problem persited. Have yet to check fuel pump, though it is a , new last year, electronic Su and sounds fime. Perhaps should check its filter, not usre how, but have never had crud out of the fuel tank.
Ignition is pertronix and in any case does not seem to be ignition related.

Any Thoughts or similar experience, solition?

Thanks, Kenn
Kenneth von Wolf Lewis

Kenn Sounds more electrical, a plug, ht lead, cracked dizy cap or or it could be a loose connection in the low tension cercuit. A miss is usually electrical where fuel usually cuts all cyls if only for an instant. DENIS

Kenn - Don't bother trying to look at the filter in the pump. first, with it's large mesh, it only filters out rocks and small birds. Second, you have to disasemble the pump to get to it (even then it is not apparent) and the chances are great that you will get the adjustments of the pump off a bit and then really be in trouble. From experience, I can tell you that in 25 years, I have never seen a filter in the AZX 1300 series pumps clogged at all. Good luck - Dave
David DuBois

I had a harmonic vibration issue with Gross Jets. At higher rpm's it felt like the car was buffeting into the wind. Replaced with standard needles and problem went away.
Paul Hanley

I had a similar problem on my '73: whenever I was in 4th gear and under load, I would get sporadic missing. New wires and spark plugs didn't do it (but I'd check yours - use a voltmeter to check resistance), but the grounding wire inside the distributor was almost completely frayed. I replaced it with a new wire and soldered it properly, and the problem was gone.
So, I agree that it sounds more electrical than anything else. Make sure you're good at the coil, and then follow the spark to the cylinders.

Have removed the petrol tank,found much rust and rust in the fuel feed line, am replacing with new, needed doing anyway, will also allow me to reapir some small holes in floor of boot and reundercoat above the tank. Have rustoleum red primed the tank and am using all new installation hardware. Did try to check the pump, before seeing the post not too, you are correct, now need a new pump. Will check all the electrics after new tank and pump are installed. A Pertronix electronic ignition is installed two years ago and all that wiring is new as is the coil, checked the plugs, new this spring, and all seemed quite happy. Tis still a mystery!! Thanks for prior and any further input.

regards, Kenn
Kenneth von Wolf Lewis

I have a friend with a TC and a TD, and when I complained to him that I have some jittering around 75mph he told me I should consider myself lucky that my car can go that fast. 60, OTOH, might be a different thing for anyone except maybe a J2 owner...
Adam Birnbaum

This thread was discussed between 31/05/2004 and 05/06/2004

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