Help! ID this problem and what to do...

[roguegeek]

Alright, let me give you my entire history with my GS. Don't worry. It's short. It's a 1997. Got it a month and a half ago with 6000 miles on it. Took it in for its 6000 mile major service which included a valve adjustment. Also had a full carb clean done to it. Had it out of the shop for about a month and it's been a beautiful ride since. Responsive. Quick. Easy. That is until yesterday.

Last night, I was on the freeway cruising around 70mph. All of a sudden, no more throttle response. RPMs dropped quick so I pulled the clutch. Even without the clutch engaged, it eventually just died all together while I was rolling down the off-ramp. Came to a stop on the side of the road and turned everything off. Gave it a couple of seconds and tried starting it up. The lights were on and the starter was turning, but the engine wouldn't ignite. Tested the battery later that night and it was fine.

So I'm there trying to start it for maybe 20 minutes. After maybe 10 tries, it finally starts. I do some quick checks and everything looks good. Get on and start riding home. When taking off from stop lights, I was getting a lot hesitation in the throttle and a lot of engine bounce. I'm sure I looked pretty ridiculous bouncing around all of the place out there. It dies 2 other times the exact same way going home and starts right up after a couple of tries. Finally get it home.

My brother (a car mechanic, but knows nothing about motorcycles) and I start looking at it. Take it on a couple of test rides with the same results. At one point, I do get a pop, but it doesn't come from the exhaust. Sounded closer to the carb than anything else. One thing he noticed was a lot of air and turbulence in the fuel line. Don't know if that's normal or not on a bike, but it's not normal on a car.

I call the mechanic that did the original service and carb clean to it. He's guessing it has everything to do with the fuel system at this point. That it's someone starving for fuel and it's just not getting it. (Yes, the tank is full and the fuel flow is on.)

What do you guys think the problem is? Is there anything I can do to either help ID the problem or even fix it? Any and all thoughts are very much appreciated. Thanx

[goat]

I remember hearing something about people having problems with the vent on the top of the tank. If the vent gets clogged, a negative pressure would build up in the tank and fuel would stop flowing. Open the tank and viola! fuel would flow again. I imagine that the pressure would also be released over time, too.

But that doesn't quite sound like your problem, if it was running fine for a while. I'm just tossing ideas out there.

What about putting the petcock in pri? That way you can rule out any vacuum problems.

[JeffD]

I had the same problem.. sort of.

Here are a few things to try,

Next time open the fuel cap and just let it flop closed, Not closed with the key but just cracked open.  This will test if your vent is clogged.

Try running on PRI, if it runs ok, then you could have a vacuum problem.

Maybe there is gunk from the fuel T to each float bowl (what my problem was)  This was solved by taking off the carbs, and shooting carb cleaner through the float bowl into the T (against fuel flow) and dirt came out of mine.

Lastly, but I highly doubt it could be the fuel screen in the tank.  Try the other things first then maybe test this one.

*air bubbles in the fuel line is normal.

JeffD

[terry1013]

I'll take a stab at this for what its worth.
1st thing, you need to do as I have and read this forum and use the search feature. Its chock full of info related to your problem. Sounds "definitely" like fuel starvation. It is either restricted or vaccum locked.

1. Knowing that you can get it restarted after a few tries I would run it till it acts up. After coming to a stop, release the gas cap and see if you get a "phhhht" noise out of the tank.  Not good if it is obviously releasing a vacuum. If your vent line is pinched a vacuum will build in the tank and not allow fuel to flow by gravity through the system. This would explain why it will run for a while before it acts up. Needs time to build vacuum through displacement of the fuel in the tank.

2. I saw another member post a problem similar to yours. He had installed an inline fuel filter going to the carbs and when his started cutting out he could look at the filter "had a clear housing" and tell if the filter was empty indicating no flow from up at the tank. I like this idea as a tool to troubleshoot.

Fuel lines can deteriorate and inside close up, like a flap valve closing off when there is flow but looking perfectly good from the outside.

Is there rust in the tank? Common problem on this forum and can clog up the system. Regardless of just having carbs cleaned there may be rust clogging things back up.

Drain the carb bowls and look at what you get. Easily done. Check the vacuum line that is at the back of the pri/res/run lever. If it is off at either end, won't flow properly.

Does the bike run ok when in the prime position? Check it out that'll tell you a few things also.  Again with the proper search you can find a lot of options to try out other than what I'm mentioning.

[roguegeek]

Ok. So I'm kind of retarded to all of this. Please bear with me.

What about putting the petcock in pri? That way you can rule out any vaccuum problems.

What exactly happens to the fuel flow when I turn it to PRI? After I turn it to that, what should I do and what should I look for?

Next time open the fuel cap and just let it flop closed, Not closed with the key but just cracked open. This will test if your vent is clogged.

Can you explain this test with a little more detail? What should I do and what should I be looking for?

Thanx for the quick responses guys.

[callmelenny]

When on PRIi(me) you are getting free flowing fuel by gravity from the tank to the carbs. If the bike runs fine this way but not in ON or RES(erve) then you probably have a bad petcock or bad vacuum line to petcock.


If opening the cap and leaving it cracked while riding fixes your problem then you have a clogged tank vent and you are developing a partial vacuum as you draw fuel out of the tank. The vacuum pressure will prevent flow to the carbs. The vent drains fuel and junk from the space around the tank opening to under the tank and out the hose that comes from the middle base of the tank. The hose could be clogged or pinched.

These are two tests for two different problems. If either one works then you have a good guess at the source.

capiche

[roguegeek]

Sweet. Thanx for all of the suggestions. Gonna try it tonight and see what happens. It will be nice if I can figure this out without a mechanic (also be a little proud of myself ). If anyone can think of anything else to try, please let me know.

[RedShift]

I'm sure we're anxious to hear your results as well.  Good luck...

[Kerry]

Just for me ... if one of your test runs takes you past a gas station, fill it up and let us know how many gallons it took.

[roguegeek]

Will do! Shouldn't be too much though. It's only gone about 50 miles since the last fill up.

[roguegeek]

Called my brother and had him fill it up. About 1.3 gallon until it was full. That's a relief because it means I'm not a complete idiot (though I'm sure there's some debate to that).

[sprint_9]

Also, be sure and take the pet-chicken off of prime when the bike isnt running, turn it back to on.  Otherwise you will have a lovely mess.

[Stormer]

Sorry if this has been solved, but I had the exact same problem. It was a fuel starvation problem.

The GS has an OFF valve under the tank, on the left of the bike, where the fuel hose fits. The mechanic loosened the tank, lifted it slightly, and reached in from the right with a long screwdriver.

The OFF valve was at a half way position, and whenever I rode a bit fast, the carbs would run dry, and the engine would die. Sit for a while, and the bike would start as usual.

Hope this helps.

[JCH]

Had the exact same symptoms, backfire and everything.  Except for me it was being out of gas (well at least down to the reserve tank)  I'm an ass.