Whats up with my 90??

[70ATC90]

I have an almost totally stock 1978 ATC 90, all it has is a cobra exhaust and a K&N air filter. The carb I have isn't stock, its a reproduction one I got from DrATV. It has been running really rich even though I have the fuel/air mixture screw set pretty lean. It runs well and I can almost get it to idle but whenever I give it any throttle it bogs down and dies. I have tried many things, I lowered the needle as far as it will go and I changed from a size 82 main jet to a size 70. What else can I do? I have an intake on it from an atc 110, could this be the problem?:wondering

[bigreddaddy]

How can it run well if it doesn't idle and dies when given throttle? Pull your spark plug and post it's condition.

[70ATC90]

How can it run well if it doesn't idle and dies when given throttle? Pull your spark plug and post it's condition.


picture this... black, sooty, carbon covered... like what a rich fuel mixture usually does to a spark plug...

[Daddio]

Has there been any work done to the engine lately? How old is your plug? If it has points are they in good shape and properly adjusted? If you don't have good spark it may appear to be running too rich.

[03 ORANGE SHEE]

air/fuel screw only works up to 1/4 throttle
main jet does 3/4 throttle and up
needle works 1/4 to 3/4 throttle
maybe this helps you...:wondering