Fuel Delivery Problem???

[BUZZIN]

On the way home (at freeway speeds) after purchasing my second '93 GS500, the bike would occasionally act as if it were out of fuel.  The fuel level never dropped to the point needing to change over to the "Reserve" position on the fuel petcock.  Most of the time when this happened it would be in the "On" postion.  By turning the lever to the "Reserve" position it would take off again after a few moments.  On one occasion it was already in the "Reserve" position, so turning to to "Prime" for a while helped.  What should I be looking for?  Could it be debris or vaccum related?

Thanks for your help.

[JohNLA]

Yes it could be debris or vacum related
Unfortanatly that is a very comon problem and could be a number of things.
I would start easy.
Check plugs and air filter.
How is the gas? Has it been sitting? If so there could be rust in the tank. Clogging stuff like the petcock or carbs or hoses.
Just some easy stuff to check first.

[cruisedaddy]

I think it may be the stinkin' petcock (the lower one, i.e., the one with the 3-way lever).  I mean the GS is a pretty cheapo rig and presumably the bean-counters were paying close attention.  The racers replace their petcocks high-quality units right underneath the tank that obviate the second one altogther BUT it would be ridiculous on a road bike to take away your reserve.  Anyone know of a subsitute for the stock petcock?  ... there have gotta be zillions of solutions so I'll investigate and tell ya what I find out.  Fuel starvation from a poorly manufactured petcock is the last problem you need!  

[KevinC]

It likely is that stoopid vacuum petcock. A lot of them don't flow enough fuel at larger throttle openings (lower vacuum).

You could try taking it apart, and putting in a softer spring. There was an earlier thread about using two lawn mower manual petcocks, one for main, one for reserve. And then someone found some motorcycle ones at Parts Depot or something for less than $10 each.

I've always wondered if there isn't a vacuum one from a bigger bike that would work. May be worth a trip to the wreckers...

[mjm]

It likely is that stoopid vacuum petcock. A lot of them don't flow enough fuel at larger throttle openings (lower vacuum).

You could try taking it apart, and putting in a softer spring. There was an earlier thread about using two lawn mower manual petcocks, one for main, one for reserve. And then someone found some motorcycle ones at Parts Depot or something for less than $10 each.

I've always wondered if there isn't a vacuum one from a bigger bike that would work. May be worth a trip to the wreckers...

It could easily be the valve on the bottom of the tank - particularly if someone worked on the bike recently.  One-quarter turn is the difference between full on and full of - just slightly angled from full on will reduce fuel flow significantly - but you won't notice except at sustained high speed or full throttle.  Checking the valve should come right after trying the prime position on the vacum petcock and opening up the gas cap to check the tank vent - I am mystified that no one ever mentions this possibility on the board.

[ejl10]

I've been having that very problem since I got my GS 2 years ago.  Its really annoying and very dangerous.  I was of the opinion that it must be something to do with the petcock... that diaphram seemed like trouble to me.

However, I recently rejetted the carbs and put a free flow air filter on, and I haven't seen the problem since.  I can't see how the rejet would solve the problem (it wouldn't have been abrupt), but a lack of air would definitely make the bike run rich, causing it to buck, wheeze and ultimately die.  Still, it doesn't seem like it should have been quite so abrupt...

This isn't to say that your problem is the air filter, but it certainly wouldn't hurt to check the airbox... make sure the filter's clean and there aren't any mice living in it!

Good luck,
Emmett Lyman