New here, hoping to get some advice on engine problem.

[chuckb2k]

Hey everyone, I just got back into riding and I wanted an inexpensive bike to mess around on since it's been a couple years. I had an 83' GS550E and it was a great bike to me. So long story short I bought a 93' GS500F. I test rode it and then I bought it 2 thursdays ago with 23k miles.  The bike ran perfectly, clutch was a little loose but nothing out of the ordinary for a 21 year old bike. I rode it around for a couple hours thursday night and again on friday. Bike was still running great. Saturday I headed out with my friend on an 80 mile ride one way. We made stops, checked out the Arizona landscape and then headed back. The bike went 80 miles one way just fine but on the way home, it started to sputter, jerk and the throttle was unresponsive unless I opened it up all the way and it eventually died.

To cut to the chase I got the bike towed home courtesy of my friend and the next day I started to tinker around with it. here is what I figured out from working on it:

* The spark was a nice fat blue color

* it would start with starter fluid but would run for maybe a couple minutes at best.

* I opened up the petcock on the frame and found the diaphragm in the back was  peeling away from the metal.

Nothing else seemed to be out of place, the carb floats werent stuck, the jets were fine as well.

I called a shop nearby and had them diagnose it and I figured why not rebuild the carbs anyways just to be sure. They said it was the petcock that wasn't working so basically what I'm asking for is confirmation of what I already know.

Would a failure in the fuel system cause the bike to jerk, come back and sputter if it wasn't working correctly?

Here's an image of the petcock as it was when I bought it, I think it was set to PRIME to mask the symptoms of it being broken. http://imgur.com/jlusM4A

[Janx101]

.. back into riding.... so you are familiar with bikes... cool!! ... im not a tech head mechanic on this forum...

going to sound silly/condescending... but its not!!! ... fuel level in tank.... you know the GS500 has like a 5 litre/1 gallon reserve level yeah?.... so many have said... "but i can hear/see plenty of fuel sloshing around in there" ....

just from what you describe it sounds kinda like its hovering on reserve level when riding... and while you have it parked on the sidestand and leaning to the left.. where the fuel pickup is... it lets it sip a bit more .. first test - add a couple litres or half gallon of fuel to see if it changes anything...

hell...  i took my bike to a mechanic last year for front suspension work... the mechanics apprentice took it for a test ride and "ran the damn thing out of fuel" ... till i walked 500m down the road and switched the petcock around  ... he was only an apprentice though!!

plus if your petcock/hose routing is messed about it wont help.... could be letting fuel seep all around the place??

[chuckb2k]

Thanks for the reply. When i got the bike i think the petcock was set to prime though which IIRC drains from the same level as the "reserve" setting but bypasses the vacumn. I didnt see any fuel seeping but after inspecting the bike top to bottom thoroughly, i came to the conclusion that its been dropped hard before or wrecked. There was tie wire holding the gas lines together, deep scratches that were just painted over and a replacement headlight.

Im supposed to be getting the bike back today but they are installing a new petcock so hopefuy that will fix the issue. If not then ill play mechanic again with it and check what you mentioned.

[BockinBboy]

I'll add to your comfort by helping to confirm:  If the petcock diaphragm has a crack/split/hole, the vacuum will not work correctly, and you can get fuel starvations symptoms when the engine is running... if it works fine when you switch to prime, that bypasses the vacuum and draws from the reserve line, and that does add to the correct diagnosis of a failed petcock diaphragm.



- Bboy