So kind of like the other question about the sputtering above 4k but mine is only after extreme fuel demands.

Run down of the problem:
When i run the car WOT first and second gear pull strong but when i get into 3rd it starts loping if you will once i get up to about 60-70 mph. At first glance I thought it was a detonation issue, so i upped the octane in the fuel to combat the problem. But it didnt change so at this point im thinking it is a fuel delivery issue. If i let out and clutch in and let it idle down a little bit rev it a couple times it goes away till i hit 4th gear and it slowly stops pulling then starts loping again.

So it is a 12a carbed motor. One solution to the problem is installing a walbro 255 but not sure if it will work or help. Anyone got any ideas?

 

welcome to the board.

is it safe to assume that the simple stuff (like fuel pump, fuel filter, carb jets, timing, etc.) have all been checked and verified to be up to par?

what carburetor do you have?

what timing are you running?

what plugs, plug wires?

what condition are your cap, rotor and plug wires in?

it makes no sense using a Walbro 255 with a carbureted 12A. if you haven't already done so upgrade the pump (Carter, Holley, Mallory, etc.) and get an appropriate regulator. be sure to change your main filters regularly.

see if any of that helps.

 

Everything as it sits is stock. I haven't messed with anything like that yet, but im almost certain it is a fuel issue. Especially with the new developments... when its cold i have to cycle my key several times to get the fuel pump to prime so that i can start the car.

The only reason i was looking into the walbro is because a buddy only wants 50 bucks for it and its brand new in box still.