cobra omc missing when warm. why?

[Drew randles]

runs fine for half an hour then only on full throttle starts missing as if only firing on four or five cylinders pull back to half power and runs fine.

[Frosty]

Check out fuel filters and tank breather. We gotta start somwhere and thats where I would go. It sounds like not enough fuel to run the cylinders at that RPM so we got to think why.

[Drew randles]

Thankyou for your response to my problem and in the morning I have a guy coming down to start looking at her so I will ask him to start there.
But why always after half an hour does it happen ? I went out today and it happened again after the same amount of time, if it was fuel would it not be a constant problem at max rpm ?

[Frosty]

Fuel filters can be partialy restrictive, Fuel tank breathers also therefore the problem may occure after time. A quick way to check the tank breather would be to temporarily remove the filler cap. Do you hear a rush of air into the tank when you do remove the filler cap? Is it fuel injection or carb?

[stonebreaker]

There was a similar problem on some GM cars. The tank vent line to the charcoal cannister (emissions) would kink, and as the gas drained out of the tank creating a vacuum, outside pressure would push the bottom of the tank up - lifting the fuel pickup out of the fuel and causing the car to stall with a quarter tank of gas still showing. Quick fix was to open the gas cap and then continue driving.