where did the gas go?

cleaned carbs recently. pitcock is vacuum opperated, but never stops letting gas flow. have kit to rebuild but havnt yet. i just clamp gas line shut when parked. however i must be loosing gas while riding. only getting about 12 mpg. i htink it might be running out airbox. Why? no gas in oil...

If your petcock diaphram is leaking,your airbox
can draw gas from the petcock and suck it through
the carbs.Your bike will run very rich and use a lot
of fuel.

Hi bubba_d . . . you might add your year and kind of bike in your signature line so when you ask questions, if the problem is specific to a certain machine it might help pinpoint a solution. That being said. . .

If your machine is like mine, there is a vacuum tube that runs to #2 intake. If you stick a vacuum line on the port on the petcock, and pull a vacuum on it, if the line gets wet internally with gas, it means the diaphragm is allowing fuel into the manifold. If you pull #2 sparkplug, you will see that it is much darker than the others if this is the case.

hope you get it sorted out.

Not really sure how a bad petcock diaphragm could make much difference when the bike was being operated... essentially during that time, the bike's petcock becomes a gravity feed. If it is getting poor gas mileage, either fuel is not being burned or there are other tuning issues... timing? valves? not enough info to say but I doubt this problem is entirely the result of the carbs or the petcock UNLESS one or more main jets have just fallen out... I have seen this happen and can't imagine it would do much for economy or performance.

1980kz650ltd
rebuilt petcock now opperates normally.still poor gas mileage. dont think jet fell out.when parked ther is a 3-4 inch spot of fuel under airbox drain tube(within 10minutes). think im spilling fuel while riding?

Bubba, The gas spill indicates the petcock IS NOT working as it should. Take your fuel line off the carburetor inlet the next time you get a chance and put it in an old coffee can. Park the bike. See if the petcock is still puking gas.

I have already told you that the the petcock isn't causing the bad gas mileage. When the bike is running, the gas burns. If it dumps, as you suspect, then one of the cylinders isn't firing. While this MIGHT be a problem with the carburetors, it could just as well be because the bike needs to be tuned as I have already also suggested.

parked it. disconnected fuel line. not a drop. think ill check a little more into things. thanks for the advice

ill take my foot out of my mouth and appologize now. pulled fuel line tonight and guess what... it pisses gas! i must need to replace the petcock entirely. for now i added an inline needle valve to manually shut off gas to the carbs. should i disconnect the vacuum line to the petcock? plug it? your advice would be appreciated.

Bubba, edit your signature and put your bike year/model in the signature. it also helps to put your location in the event someone near can come help.

What type bike is this? What type carburetors? I suspect the right answer is to install a Pingel adapter plate and aftermarket gravity petcock but hesitate to make any recommendation without at least knowing a little about the bike being discussed.

ive tried to add my bike to my signature but i havnt figured out how. it is a 1980 650 LTD. with mikuni round slide carbs. as far as i know the bike is stock. has 9700 miles on her.

well obviously figered out how to add signature.

looked into these pingel adapter plates. sounds like something i will try. not sure what size i need though... the petcock appears to be stock. any ideas?