Is there an eazy fix?

[Alan_nc]

So if I'm riding a steady 60 mph down the road every 1/4 mile (or so...never exactly the same) it feels like someone has ever so gently applied the brake.  Just happens for a second or two and then back to normal.

I made sure the brakes are not rubbing - so that is not the problem.

It only seems to happen when I have the petcock set to "on"

If I turn it to 'prime' it seems to run with no problem.

I could always run on 'prime'  but really would like to know what the problem is.

Thanks in advance.

[codajastal]

Sounds like classic fuel starvation.
If you have inline filters, remove them, If not then maybe time to change you fuel lines.

[Big Rich]

Yep - fuel starvation causing the mixture to lean out. Could be an inline filter like Cods mentioned, or the gas tank vent line. Try leaving the cap slightly open (don't want to spill any). Also check the routing of the carb vacuum line - not the one going to the petcock, the one that vents towards the airbox. If that line is pinched, the carbs can't replace the gas going to the engine with air.

[ace50]

I'd say check your petcock diaphram for pin holes or something. Setting to prime bypasses it, that's why it clears up on prime.

[yamahonkawazuki]

Sounds like classic fuel starvation.
If you have inline filters, remove them, If not then maybe time to change you fuel lines.

our engines are as durable as industrial sewing machines. I agree with the above

[bombsquad83]

Fuel starvation seems to be a common issue with the stock petcocks.  I believe it's due to the ethanol in gasoline degrading the diaphragm in the petcock.  You will find many threads if you do a search for fuel starvation.

[yamahonkawazuki]

Theres always the pingel swap