cant go over 65 mph???

[raiderfan2003]

I am new to the board but ive been trying to troubleshoot my bike for a few months now. Ever since ive had my bike for over a year now i cant get it to go over 65 mph and i dont know why. its a yamaha xs650cc custom bike. it has alot of power in the first 4 gear and even the 5th but when i get up to around 65 mph it seems like it just wont go faster and i cant figure out why. ive taken it to a few mechanics and they couldnt either so far. ive got it in one now and im hoping the can get it going to where it needs to be. when i get that fast i keep turning the throttle and it acts like it wants to go faster but just wont. it almost seems like it misses at that speed. any help would greatly be appreciated! i was wondering if rust and paint rust inside the tank could be causing this as well. -Shane

 

[lettle]

Just some simple checks- Is your timing set correctly? Is your ATU advancing? Valves set correct?

Do RPMs raise but no speed increase?

*****Are you running 2 petcocks or one? if only one petcock, you may not be giving your carbs enough gas, or not enough air may not be getting into the gas tank, creating a slight vacuum

Lawrence

 

[jamesgs4]

rust and paint in your tank will get into your carbs and clog them all up. put a filter inline and clean your tank, then clean your carbs again.

 

[retiredgentleman]

If it has diaphram carbs..............check that the diaphram does not leak.

 

[littlebill31]

What year, mods, carb style (CV, VM, Bs34, BS38)? If you are in, say, 4th gear, does it do the same thing. Meaning it acts like it could go faster. If it is a diaphragm carb it could be the diaphragm. These type of carbs work on throttle position too. So if you have a good idle to 1/4 throttle, then a good 1/2 to 3/4, but a flat spot at 3/4 to full throttle, it could be the main jets.
To check for a leaking diaphragm, on the carb, where the air cleaner goes, you will see an oblong port on the top. Reach your finger in the carb body and lift up the slide body, cover the oval/oblong port, and release the slide. It should fall very slow. That is a good sign. Fast means it's torn