Lack of fuel when not on PRIME

[Jakobzen]

Hi guys. Im a very happy new owner of a '79 GS850G. Only owned it a couple of weeks, and have no prior mechanical knowledge. I have a problem, which I am sure you know a good answer to. The bike only seem to get enough fuel when the fuel petcock is turned to PRIME, when put on RES or ON the bike chokes after a short amount of time. So I'm thinking: no vacuum. Should I replace the petcock, the rubber vacuum hose or just try to blow compressed air though the hose? Any other suggestions?

[Brendan W]

On any new to me bike I would have the tank off and petcock removed if only for inspection and cleaning. Once you are that far in you can check the vac hose is clear, fits tight at each end with no splits.
The petcock itself is a simple device easily opened for inspection. Repair kits have mixed reports. New might be better if it is the problem. In the meantime turn to ON or RES after a ride. On PRI fuel can get past the float valves into the crankcase dilute the oil and that can damage the motor. Fairly common event on these machines.

[Steve]

First things first, ... do you have a vacuum hose connected to carb #3?

Keep in mind that carbs are numbered from left to right, as you sit on the bike.
Carb #1 is under your clutch hand, Carb #4 is under your throttle hand.

If your hose is connected properly, verify that there is a vacuum signal at the carb end of the hose when the bike is running. If that is good, check the diaphragm in the petcock.

.

[Big T]

as Steve said, hook up a new hose to the vacuum port on the petcock and suck on it to see is any fuel comes out
If it does, connect to #3 carb

If not, drain fuel tank and take off the petcock face, twist the level until it pops out and see what you have in there. The passages may be clogged with old fuel or corrosion, or the rubber disc may be deteriorated. If it's one of these things, order a new disc and the O ring for the lever and you're good to go

If the diaphragm is bad, you may want to order a new petcock at about $70. Rebuilds have a low rate of success

[Jakobzen]

Thanks guys. I'll check the hose for vacuum. I am so happy I found this website - its a fountain of wisdom here.

[geol]

The carbs vent through plastic tee fittings located between 1&2 and 3&4 carbs. If these are capped/blocked then the floats won't draw gas or will puke gas. Also, before you try anything else, open you gas cap and check flow on prime. If the vents in your cap are plugged, it won't flow well and with the cap open, the tank is vented. Time for a new gas cap as there are no parts to rebuild a Suzuki cap I know of. The other suggestions are fine but it is easy to open your gas cap and to check vents.

[Jakobzen]

Haha, easy fix. The PO had the bike resprayed - and didn't connect the vacuum hose to the tank. He must have thought it was an overflow hose. The vacuum port on the petcock was connected to the fuel gauge. It works perfectly now. Thanks!

[JJ]

I'm glad to hear it was simple. Enjoy the bike now!

[hillsy]

It must have been running like crap. I had my vacuum hose come off whilst riding on one of my XJ900s once and it was stuttering and backfiring like crap - even with the tap on prime.