Fuel supply issue I think??

Still Having an issue with my 1980 xj 650. After a top end rebuild my first problem was a float set to high and filled the sump with fuel. After fixing that it would bogg down when trying to accelerate over 100kpm and following advice off this site I replaced the butterfly shaft seals. This time I bought a color tune plug from Charcal and after balancing and tuning the carbs it starts and runs like a dream at idle and under acceleration. From 0 to 100kpm its fine but try and go over 100 kpm acceleration drops and under hard acceleration it develops a miss or a cough. After reading through many threads on this site Im thinking it may a fuel/supply issue. I did put a new kit in the petcock and have tried running it in the prime position with no change. I have an inline fuel filter fitted and have fitted new fuel and vacum lines. Am i barking up the wrong tree and could it be an electrical problem or both?

 

Did you try disconnecting the fuel line from the carbs and routing to a container and try applying vacuum to petcock and see what kind of flow you get!?
Some times those petcock rebuilds don't do all that good...
I replaced mine with a manual petcock and all my troubles went away!
Now I only have to remember to shut it off when I park it for several days.

BTW what does 100kpm mean?

 

No I havent tried that. Im considering a new petcock but due to the cost of a new one I need to rule ouy that its not something electrical.

KPH = kilimeters per hour

 

There is also an in-tank screen filter on the petcock suction and that may be cruded up too