[hipnerd]

I'm very new to riding and I've purchased what I believe to be a pretty good starter bike- a 1983 GS550L. It's got it's nicks and bruises, but so far I am quite pleased with it.
The one problem that I can't figure out has to do with fuel supply. When I run it in the prime position, there are no problems. But, when I switch it over to the "run" position, the bike stutters and/or stalls when pulling out of first gear. Also in the run position it sometimes stutters in higher gears, but does this only once in a while and I haven't figured out a pattern as to when to expect it. This has provided dangerous and embarrassing situations that I would like to put an end to as soon as possible.
My question is, what exactly does the "prime" position do, and, what could be causing it to run so poorly in the "run" position. As I said I'm very new to this so even the most basic responses are welcome. It may help to note that there is a slight fuel leak, location(s) as of yet unidentified. I am greeted every morning to a small wet spot on the ground and I am only getting 50-70 miles per tank (roughly 2.5 gallons). Also, I think I have an after market exhaust system installed, one with all four pipes running together on the right side of the bike. I'm not crazy about the sound the exhaust makes, and I'd willingly replace it if that might be the source of the problem, but I already know that parts for this bike are going to be tough to come by.
Any suggestions?

 

[Uncle Bob]

First step is to find that fuel leak, it's most probably the source of the problem and a safety hazard. Wouldn't want you to go up in flames.

Your petcock is vacum controlled and does not have an "off" position.

Pri - Prime should be used only for hard starting situations and after long periods of time without running. The bike is gravity fed (no fuel pump) and Prime opens the valve to let the fuel flow. Do not leave it in this position when not running or you risk putting fuel into your oil from overflowing your carbs.

On (run) - Is the normal position that your petcock should be left in. The petcock is controlled by engine vacum. When you turn the engine off the petcock automatically closes.

So if you have a leak in your fuel system the vacuum is probably sucking in air with the fuel depriving the engine of enough fuel.

 

[hipnerd]

Solved problem (?), new question

Thanks for the advice. After learning how the petcock worked in the prime position, I stopped leaving my bike in the prime position and I think this has cured the fuel leak. There are no puddles of gas on the ground anymore. Is it possible that the fuel that was leaking out was caused by the petcock being left in prime?
Also, due to a response I had read on another topic on this forum, I stopped using 93 octane fuel and switched to 87. I think this may have been the reason why the engine was fouling in the "run" position. After the switch it's been running much more smoothly. Does this sound like specious reasoning, and should I keep looking for reasons why it wasn't running properly?
Finally, as I said before, I'm very new to bikes and am not really sure if what I'm experiencing is normal. But I think my bike may be revving a bit on the high side. At 65-70 mph the tachometer is reading about 7-8 thousand rpms. It seems like an awful strain on the engine to be running so hard for long distances, and it eats through gas a lot faster than I had imagined a motorcycle would. Is this a normal speed to run a motorcycle engine at, or is there something wrong. I believe the jetting on the carborator may have been fiddled with, if that adds any insight.
Thanks for the response. I love this site and I am learning lots about the bikes.

 

[Uncle Bob]

Hard to find specific info for your bike but would guess that 7 to 8k's would be in the normal range unless the front or rear sprocket was changed or you're feeling clutch slippage. After all max speed for your bike is about 100mph and max RPM is about 11,000 rpm so 8k'[email protected] mph sounds right.

As for the change in octane ratings, this could have caused the engine to not run as well. And if you were leaving it in the prime position you were drowning it.

Glad everything seems to be getting into line for you.

 

[Weazel]

Congrats on the bike, I'm a newbie with an older (but awesome) bike, a GS-650 G shaft drive. I haven't had any problems with my bike *knock on wood* but my friend with an older bike was experiencing the stumbles, and it was his carburator boots starting to crack, pulling more air in and displacing fuel (or so he was told).

I never put the bike in prime, only once to drain the tank before winter (and that was sloppy, so never again). In FL I bet you don't sweat "winter" too awfully bad.

For the RPMs, I know mine will go about 12mph/1000 rpms, so at highway speeds I'm in the 5k-6k range (with a bigger, shaft drive bike). I don't think you're turning excessive RPMs, but if you're worried about a slipping clutch or something, just get going down a hill coasting at like 30 and put it in top gear, then let it glide. If you're turning half the RPMs you are at 60...then your clutch is fine.

Good luck and enjoy the bike!

 

[hipnerd]

Thanks

But finding a hill in South Florida is about as easy as finding snow. Interesting point on the carbs, the bike has started running a little roughly so I'll take a look at that. Did the carb boots have to be replaced, and if so were they tough to come by? And plus, now that I think of it, what exactly is a carb boot? I'm new to all this biking lingo. I know there are two rubber cone shaped "sleeves" that come out of the intake, but I was under the impression that those were airboxes. Am I showing too much of my ignorance here?