Topic: cb750f runs like crap on reserve.

[JustMe]

ok i could use a little help here guys. the bike is a 75 cb750f and it runs great until you switch it to reserve then it misses and sputters and bogs out. sometimes it will stay running but still misses until you get over 4krpm and then it runs like normal. i removed the fuel line to check fuel avaliablity and it runs the the petcock the same for normal or reserve. So i'm at a loss for ideas, any help out there?

[Killer Canary]

Just a guess, but if it's like a 550, there's a straw that presses into the top of the petcock inside the tank which supplies fuel to the "on" position while a crescent shaped opening next to the base of the straw supplies "reserve". Maybe this opening is plugged.

[scondon]

Crap sinks Rust, debris and water will all settle to the bottom of the tank. "reserve" draws form the bottom of the tank so if it's seldom used there can be a lot of crap(God, I love that word) in the gas you're feeding your carbs. On your next fill-up try riding away in the "reserve" position. If your situation improves, keep it on reserve until half a tank is used up. If not, then a good cleaning of the petcock may be in order as Canary suggests

[TwoTired]

Well, I suppose I can supply as little help as the next guy.

The petcock assembly extends into the fuel tank with a stand pipe and a fine fabric filter over the entire intrusion.  The difference between on and reserve is whether the stand pipe is selected, drawing fuel from about two inches above the bottom of the tank (on) or from the base of the tank (reserve).  Further, the base of the tank is where contaminants will settle.  If the filter fabric is damaged, this crud goes to the carbs, when reserve is selected, and any bits larger than .016 inch stick in the slow jets or other parts of the carb internals.
Have you checked the carbs/tank for fuel contamination?

[750FSS]

sounds like we have the same thing but back ward.

http://www.sohc4.us/forums/index.php?topic=2968.0