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MG MGB Technical - High speed misfire

I have a '74 'BGT that I use for autocross. At the end of a 2 minute run, it starts to cut out and sputters across the finishing line. I've got some ideas on the cause. Thoughts?
Matt

Matt - Check your fuel tank for proper venting. If the vent is clogged, it will draw a vacuum and cause the symptoms you are seeing. Good luck - Dave
David DuBois

Matt: Does your fuel tank have baffles? If not try running with the tank a little fuller. I don't think a vent problem would show up on a two minute run. Clifton
Clifton Gordon

Is your tank the original one, or has it been replaced? If it is the original tank, it is possible that the pickup tube has holes rusted through it causing it to suck as much air as fuel. I had this problem on my '72B.
glq Greg

The tank is a brand new replacement and fuel starvation was on my list of causes. The last time it did it, the car had half a tank. It could have sloshed around enough to starve it, but I filled up and drove home and it still seemed a little off. It has a solid state fuel pump that seems to be up to scratch.

Something I've also considered is coil and or distributor. Both are new and the coil is a higher voltage piece. The distributor is a 45D. I prefer the 25D just because all my other cars have them, but really, I don't know which would be better. The points etc. are still there which may be slacking off at a constant 5000 RPM.

The last thing is the carbs. It has rebuilt HIFs that function well on the street, but I don't care for the self adjustment feature
Matt

How are your vent pipes hooked up at the carbs Matt?
mwhitt

Vent pipes eh? I assume you're referring to the vents that used to go to the emmissions system. They are blocked off. What I have is fuel supply and overflow. The vents on carb inlet face are vented as usual. Should the carb body vents be open to atmosphere?
Matt

This thread was discussed between 30/01/2005 and 31/01/2005

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