cleaning/rebuild frame petcock

[infamouz k]

how bad is it? my bike only runs when its switched to res

[adidasguy]

Do you mean RES or PRIME?
If PRIME, then you're probably missing the vacuum line to the petcock.
If RES, then you could be low on gas or your ON line is pinched.
The vacuum makes RES and ON work. Unusual for only one of those settings to function unless low on gas as the same vacuum opens the same diaphragm.

[infamouz k]

over half a tank of gas,my lines are not pinched. i cleaned the carbs,changed spark plugs.she runs lean. everything is stock,no mods.i switch to run its good;but it seems to use the gas in the bowls and then dies.on res she runs good as long as i dont give her more than 1/4 throttle....any more and she bogs down and sputters at 5-6 grand

[bombsquad83]

It often looks like you have more gas in these tanks then you actually do.  Look in closely in the tank with the bike on the centerstand.  You should be able to see the gas level on the petcock.  If it's below the top 1/4 of the petcock, then this is why you are starving it on ON.  Just need to add more gas.

[infamouz k]

i can fill it to the brim and the same stuff happens. it started after i had too much oil in the bike

[oneNonlyTu]

For your first question, no it's not hard to clean the petcock. But it might not help. I've been thinking about this whole fuel starvation thing for awhile now. If you look at where the tank, petcock and carbs are relative to each other it suggests  that this is simple a "pressure" issue.

In other words when I'm full tank there is enough potential energy for fuel to go down to petcock then slightly down more but mostly over and back up a little to the float bowls. When I'm half tank (less pressure from fuel above it) the remaining fuel has a tough time "dropping" down to the petcock and then if vacuum is present continue the trip to the Y-tube to floats. On top of which, the line where the "on" hose goes kinda goes up into the petcock.

"res" is lower in your tank than "on" so there's more pressure (from more fuel above inlet) for it to drip down into the carbs.  Solution might be new petcock or use "PRI" if you can deal with turning it to "on" when you park.

[infamouz k]

i havent really thought about it that way......what about just bypassing the damn thing?lol  aint that why we have floats to keep fuel from over flowing the carbs?

[oneNonlyTu]

Well yea, but that's assuming two tiny little plungers is going to hold a full tank of gas from filling the carbs.  I'd rather the peace of mind that a rubber diaphragm and spring is sufficiently blocking off fuel.  My "on" switch is now my "OFF" switch.