hi i have a cortina with a 250crossflow that i race speedway in. it has yella terra speedway cam kit rockers etc. we are limited to running 350 holley with standard manifold,we have done alot of work machining out the manifold and run electronic distributor race leads and cold xf plugs because the car has a great cooling system never gets over 70 degrees really. the problem is at mid to hi revs the engine starts to make a weird flutter-missing kind of noise and loses probably half its power. we have spent hours trying to solve it. any suggestions would be greatly appreciated. cheers.

hi, welcome to fordmods...

what fuel pump are u running? also what size fuel line, bigger tank pickup? and what size needle and seat in the 350?

hey mate we run electric holley and manual pump 5/16 fuel line and pick up and 110 needle and seat. it revs out really well when its not under load but when the car is under load is when the problem starts

You'll need 3/8" fuel line, from the tank ( pick up ) to the carby.....what size jets????...64's would be ok, maybe up to 66's,..... what power valve????....try a 95.
Is the dizzy regraphed???.........what comp ratio are you running????....10:1 or better, use MSD ignition or ICE ignition.

Have you tried warmer plugs?
A 'cold' plug transfers more heat away from the tip.
Plug heat rating is not about coolant temperature, its about combustion and plug tip temp.
Its a balancing act between not too hot to burn out the tip, and not too cold that the plug fouls up easily.

70deg sounds pretty cold, could be an issue there too.