Hey everyone, so heres my deal. 85 fxr stock motor, thunderheader, mikuni hsr42, stage 1 air cleaner. The bike starts dying out at around 70mph or heavy acceleration, it didnt do this when I bought it but it has been for a while now. I changed out the jets on my carb but they problem persists. Ill admit i know the least about carbs out of anything. Im broke rightnow so I cant take it to a shop. Any sugestions would help, Thanks!

 

Check any fuel filter, petcock screen, and anything like that for crud that may get sucked into a filter when there's high fuel flow. With a 30 year old bike there may be material flaking off in the tank and causing blockages.
You should try posting in the carb section, too.

 

Check the intake gaskets too.

 

Agree with nevil, Pull the petcock and change the filter, be sure to blow through the petcock in the on and reserve positions. Should work assuming you have flow through your new clean jets and the new jest are the same size as the old jets that worked for years.... While the petcock is off, remove the bowl from the Mikuni and let the float drop. After you install the petcock and new filter, let some gas flow through that needle and seat on the carb. Work the float up and down and confirm the gas flows good.

If all else fails, check your float height on the carb because if it is set too low there will never be enough fuel to run wide open.

 

Thanks for the replies, I just ordered a new petcock and fuel filter. The old petcock looked like crap anyways. as far as the intake gaskets I put new ones in not too long ago and check for leaks. If it is a float issue or something else with the carb Ill probably just have to wait till I can take it in. Cheers

 

Sometimes the needle and seat can get junk in them and just removing the bowl and letting the gas run out will rinse the problem away. I usually take a can of carb cleaner and place the little tube into the exposed jets to blow through up into the carb. i also use it to clean the bottom of the bowl then put it back with the 4 screws. $3 can carb cleaner and 20 minutes of your time may save $60 an hour or more labor.

Just be careful not to bump the float and bend the tang which would change float setting and be careful not to let the float hinge pin slide out which would drop the float and needle ASM. Gently lower the bowl and gently replace it after the cleaning.