Bike not getting fuel...

[Chester Gunn]

Well, thanks to the help from this forum, I was able to get the carb synched and it really is running better than ever. But, when I got it out on the road, I ran it up to 8,000 rpms and it was singing like a bird. Shortly there after, it quit running!! I got off the bike, looked at the fuel filter and it was empty...changed the fuel lines around on the tank, and after several minutes it fired right back up and ran like a champ. I proceeded back to the house, only for it to quit on me again. This time, I didn't push it. I keep the revs really low and I made it back home (5 miles). After returning home, I made several laps around the yard, shut the bike of and it started right back up immediately. It seemed like when I pushed it hard, it wasn't getting enough fuel. When I backed off, it seemed to run just fine. I don't think that this was a result of my carb synching, but I couldn't be for sure.. The bike is a 1983 GS 650 Gl..and after I synched the carbs, she was running like a DREAM!!! I just wish that it had a 6th gear. Please help me figure out my fuel problem.
thanks
Chester/Chula, GA

[chef1366]

Sounds like a bad petcock.

[Chester Gunn]

Well, the tank did sit out in the rain. Could that have caused it?

[chef1366]

Twenty some years old will cause that.

[LarryA_Texas]

Well, the tank did sit out in the rain. Could that have caused it?

Petcock could be bad not allowing fuel to flow properly. They are not that hard to take apart and clean out.

You said you can see the filter, so you have an in-line filter. Is the stock filter still inside the tank? Fuel filter in the tank could be mucked up, allowing fuel to dribble enough to get it to run at low RPM but not at the higher speeds. With a filter clogged it might not stop the fuel alltogether but could be flowing slowly. The line might be kinked. Any of those could cause the symptoms you describe.

Try this first: Take the line off the petcock. Attach another length of hose to the petcock with the end of that hose in a bottle or something you can drain gas into. Then put it on prime and see if the fuel flows freely. Then put it back to run (assuming you have enough fuel in the tank). The flow should stop. Now suck on the vacuum line attached to the petcock. Fuel should flow freely as before. Then try it again on reserve. That would test the petcock.

If it turns out the stock filter is still there but is clogged you can just clean it. Don't remove it completely even if it's damaged or you have an in-line filter. You need that pipe to make the reserve position on the petcock work.

I'd bet it's fuel delivery, not what the carbs are doing with it.

[LarryA_Texas]

water in tank

Well, the tank did sit out in the rain. Could that have caused it?

Water in the tank will sink to the bottom. If you suspect water follow the steps I describe in the previous post by draining into a glass bottle while in the RESERVE position. You see right away if there is any water in the fuel. Water will come out first from the bottom of the tank.

[Chester Gunn]

Well, I removed the petcock from the tank and completely disassembled the unit itself. The fuel filter and the fuel flow side was completely clear. The vacuum side was a different story. The holes were clogged with a black, tar looking substance. I took a straight pin and cleared the holes as best I could. I then blew through the fitting and it seemed unrestricted. I put it all back together and the bike ran fine, for a few minutes and then it shut down again. Like before, the glass fuel filter was empty....

I examined the diaphram while I had the petcock taken apart and it seemed to be ok. I'm just wondering if there is more of that "tar like" material that became dislodged and once again restricted the holes. If that is the case, is there anything that I could soak this piece in to disolve this stuff? The only other thing that I can think of is that the vacuum line that runs from the carb to the tank takes a pretty sharp bend, but it does not appear to be kinked. I know this sounds like a rhetorical question, but would the slightest restriction in the vacuum line cause the fuel not to flow freely??

Or, should I just try and find another petcock?

Thanks
Chester/Chula

[1978GS1000custom]

yes it will cause it to starve for vacuum. a cracked (old) line will do the same. some gumout carb cleaner from autozone will disolve the black tar stuff which is bad gas turned to varnish. everything has to be in good condition for the gs fuel delievery system to work correctly. what happens when you try to run it on prime? cliff

[Chester Gunn]

Okay, the plot thickens. I went out and removed the petcock only to find that the little holes in the screen that were clogged had not "re-clogged"..But, I went ahead and cleaned it up and put it all back together...Here is the real mystery....What I found was that on prime and reserve, the fuel filter stayed full, even at high revs. But, when I switched it to the "run" position and revved the motor and the fuel level went down in the glass fuel filter.

My question is this, what would cause the impedance of fuel flow while on the "run" position, but not the prime or reserve setting?

Thanks
Chester/Chula

[tkent02]

Low on gas in the tank?

[Chester Gunn]

Low on gas in the tank?

No, the tank was over half full??

[Chester Gunn]

Another stupid question....Can I just run the bike on the reserve setting??

I honestly and really don't know??

CG

[Killer2600]

Another stupid question....Can I just run the bike on the reserve setting??

I honestly and really don't know??

CG

Yes you can but you don't want to know what happens when you run out of gas while on reserve---you end up pushing the bike to the gas station

Better to run on the main supply so if you run out you can just flip over to reserve rather than push to the pump.

[jjmaag]

Have you checked the tank vent? Try running with the cap loose.

[LarryA_Texas]

Petcock 101

Another stupid question....Can I just run the bike on the reserve setting??

I honestly and really don't know??

CG

I don't want to get too elementary here but let's start from the beginning. I think you may need a short lesson on how the petcock works.

When on RUN fuel flows through a tall pipe inside the tank through a little valve in the petcock to the carbs. As the fuel level goes down eventually that pipe no longer gets gas. Switching to RES allows fuel to flow from the bottom of the tank. This arrangement allows you to continue to ride after the main supply has "run out" of gas so you don't have to push it to the gas station. It's very simple. But there is no harm in running on reserve...you're just using a different pipe to draw fuel out of the tank.

The valve mentioned above? It's really a rubber diaphragm with spring on one side to push it closed. To pull it open depends on Vacuum. It could be from anywhere (you can suck on the pipe) but the only vacuum source in a GS is the engine is through the #2 carb. That's the second, smaller hose on the petcock. While the engine is running vacuum pulls the diaphragm open and allows fuel to flow.

The whole reason for this valve is so that when the engine is not running fuel will not flow to the carbs. This helps prevent overflow, leaking, and filling your crankcase with gas.

Since there may be times when you want fuel to flow without the engine running they put a PRI position. As you rotate to PRI inside the petcock a littlle pin is pressed against the diaphragm to hold it open mechanically reguardless of vacuum.

Now, if your fuel flows when it's in PRI but not in RUN or RES, then it's a safe bet that the diaphragm isn't opening via vacuum. More than likely you have a bad hose to the #2 carb or the diaphragm is blocked from moving, has a hole in it or is just too stiff to move any more. They are easily replaced in a petcock rebuild kit.

If it runs when it PRI or in RES but not in RUN, then more than likely the tall standpipe for the RUN position is blocked and not allowing fuel to passs down into the tank. You have to take the petcock off of the gas tank. Then clean out the filter that sits on top of the petcock and then REMOVE the filter...it's probably stuck pretty well in there. You'll have to force it a bit but be very careful. It is easily damaged.

Even if you do screw up the filter you still need to put it back because that filter has the standpipe to make the RUN/RES positions work. In this case put the filter back in place even if it doesn't have any filter screens any more. Then put in an in-line filter to protect your carbs from dirt.

When you get it off the petcock you can blow everything out with carb cleaner and make sure the passages are clean. The little metal clip that has the words RES-RUN-PRI on it just snaps off from the sides so you can pull the valve out and clean it out, too. Snap it back on, stick the filter on top, load it back onto the gas tank...be sure the large o-ring is still sealing and you're done.

Good luck.