<cut from another thread>


What everybody is saying is that your stock vacuum actuated petcock isn't flowing enough gas for wide open throttle uses for you on your bike under those particular circumstances.

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Let's run this thought out a bit -- you are running WFO for a bit and the petcock can't keep up because vac pressure is low and the diaphragm is stiff & old so your your bowl level is getting critical low due to only a dribble of gas getting thru the petcock ....

Bike is turning max rpm and should be making max HP, but instead it's leaning out to the point it sputters and pops.   It leans out to the max and gets really really hot instead.


THEORY

Have we just explained the (not so rare) sudden onset of oil consumption issues, the more occasional piston/rings suddenly getting mangled up and the very rare holed piston and popped off valve tulip head?


If I were a heavy wrist-ed wicker I'd get rid of the stock petcock and go to a Raptor simply to forestall any massive "overheating the engine" issues down the road.  

Stock petcocks will fail eventually on you (given enough time, anyway).

Good point about years of age being the determinant on the "stiff diaphragm" part of the issue, not simple miles per se.


I'll fix the poll accordingly.

The only machine on which I have had vacuum petcock issues was a Honda 125 Aero scooter. It was a two-stroker, and the intake manifold vacuum came from the crankcase. It would not run steadily at wide-open throttle, but ran just fine when the throttle was slightly closed. I don't remember the model year, but I bought the machine new so age should not have been a factor.

Well, NOW I get it. Even IF my fuel is flowing fine at cruisin around, hard accelerating & giggling levels, it May Not flow well enough at sustained wide open throttle settings. Ill not be running wide open for more than a few seconds while this petcock is delivering the gas. It wont be on the slab again till it has a raptor on it.

Heck, that's a surprise to me -- so many bikes having petcock issues that are less than 10 years old.

Do you suppose that 10% alcohol showing up in regular gas played any role in this larger amount of "newer" bikes having the issue?

Or have the vac actuated petcocks been a crock all along?

One bike over 20 years old!  That's me!

Most of us prefer to have a gas reserve (kinda nice thing to have).

Prime works, but gives you ZERO reserve and some sudden surprises !!!

But you can get some primo extra exercise running in Prime all the time

  -- very good cardiac exercise pushing that bike ....