Hey all, I picked up a non-running '92 GS500 a few months ago. I have not had any time to look at it, but I am hoping to get started on it in the next few weeks. The previous owner provided me with this video of the last time he had it running.

Any thoughts on the cause? I am also curious how I can describe this condition so that I can search more easily on my own. Any help is appreciated!

I would say by the time it runs right you will know the inside of the carbs pretty well (clean the carbs and the inlet screen in the tank) rinse repeat with fresh fuel.

And...Welcome to the forum! 

Defo fuel delivery issue.

Due to the nature of the idle, I would also say to check to clean the carburetor,
aside from that, also replace the air filter. It's not going to be the reason of the rough idle, but you might as well do that, and get an inline fuel filter on this bike!

Nix on the inline!... wasted effort!

As others mentioned it's likely either fuel or air, but more likely it's dirty carburetors and some crud is clogging the tiny fuel pathways in there. I've also heard that bikes that sit can build crud up in the carbs.

This bike definitely sat for a while. Sounds like carbs are first. Why is the inline filter a waste of effort?

Here is my preliminary plan of attack:

Clean carbs. Fixed?
Vacuum leak test. Leaks?
Carb rebuild. Fixed?
Clean petcock. Fixed?
Clean tank vent. Fixed?

From there, no idea what else to try. Hopefully that covers it though.

As long as it's a MC inline filter your fine, automotive filters don't work in a gravity feed system.

And when you have cleaned them out.....synchronise them 

I see inline filters on this bike as superfluous and unnecessary. . Seen a lot of posts about bike fuelling issues that went away after filter removed again.... plus its an extra cut in the line to potentially leak...

Even though manufacturers are notorious tight stars when it comes to equipment on bikes and equipment. . The cheap cost of a cheapo online filter could have been included if it were truly needed? ..

And the in tank filter screen... that is ultra fine mesh! .. paper is going to improve that?

"But where I get my fuel it's sometimes murky and I don't want a murked up engine!" , really? Its murky and you go back there? And/or .. you don't check the first dribble/squirt of fuel when you fill the tank?

But that's just my view.. :rolleyes:

You may also want to check the valves and then sync the carbs as sledge suggested. Replacing the fuel lines may not be a bad idea either since they're cheap. Same with spark plugs.

Some questions for y'all:

Are fuel lines something that needs to be ordered from a parts catalog, or can I just go to an autoparts store?

When I am testing the carbs, can I leave the tank off and just attach a hose to the carb fuel intake and leave it sticking straight up in the air with some gas in it?

On a similar note, is there any reason for me to reattach the airbox while testing the carbs?

Thanks in advance!

Quote from: Petorius on April 05, 2015, 11:40:08 AM
Some questions for y'all:

Are fuel lines something that needs to be ordered from a parts catalog, or can I just go to an autoparts store?

When I am testing the carbs, can I leave the tank off and just attach a hose to the carb fuel intake and leave it sticking straight up in the air with some gas in it?

On a similar note, is there any reason for me to reattach the airbox while testing the carbs?

Thanks in advance!

you can get them from an autoparts store, just make sure they are RUBBER. and not plastic, I wasted 18 bucks on nylon lines, because I was stupid and in a hurry...

What's the problem with plastic? The ones that are on there now are plastic. I already don't like how they are stiff and hard to route.

Quote from: Petorius on April 05, 2015, 11:59:23 AM
What's the problem with plastic? The ones that are on there now are plastic. I already don't like how they are stiff and hard to route.

they soften up when they have gasoline in them, I soaked mine in a gas-can before installing them. rubbers that is.

the plastic ones ARENT soft. at all, they are impossible to work with!

Hmmm yes..  for the 'cost saving' and subsequent wait/delivery time of the whizzbang online fuel lines. . . I just went to my local bike shop with my old hoses and said 'give me a metre of that' ... 5 mins later I was on way home again... still under 20 bucks and I had it NOW ... nothing wrong with generic rubber fuel hose!

There are a million fuel lines of late. As well as a million colors in each.
Tygon is one, I have a silicone line that I really like, and put one in the skorpion - its fuel line is all of 2" long, and stupidly it sprung a leak as I rolled it out to the driveway. WTH ... it was hard as a rock, and I moved the tank just enough to split the seal it had @ the carb and ... leak.

The basic observation is this. These things get brittle due to sunlight, all of em, regardless of the material. I've noticed the ends that connect to the tank on the GS being nice and soft and the rest being hard as a rock so much that you move it, it will break right there.
So get those tygon lines, and slip over them a black rubber protective bicycle inner tube and it should last a lot longer than a year or 2. Or, who cares, replace it every year.

Cool.
Buddha.

Total mileage on the bike ? Old bike.

Worn valve guides/seals, sucking air there - spritz some starter fluid around the head cover gasket, see if you get a change in rpm . 

YMMV.

I cleaned the carbs out, got rebuild kits for both, set the float height based on the book, and made an auxiliary fuel tank to test everything out. It ran, but idled poorly, so I made a sealed-bottle carb sync device and got the carbs balanced as best I could with the idle at 1200 rpm. I noticed that they were pulling even vacuum at 1200 rpm, but went slightly out of wack as I added throttle. Not enough for me to care. After a while, it seemed to idle good, with good throttle response, and the throttle would drop back to idle smoothly (but a bit more slowly than I am used to with my EFI bike).

I decided to ride to work the next day. It did not run well at first startup, the idle seemed slightly wobbly, and it would bog down if I tried to slip the clutch and add throttle simultaneously from a stop (below 4K rpm). As soon as I came to a stop in traffic (on the highway!) it bogged down and cut out on me. With a bunch of throttle, it came back to life, but I realized it wasn't going to work under 4K RPM. I dialed the idle up to about 4.5K and made it to work like that. It wasnt pretty. It seems to run OK above 6K, crappy from 4.5K-6K, and unrideable below 4.5K. I am confused because it seemed to be idling at 1.2K and revving from idle without any issues when I was testing it the day before. As soon as I put a load on it, it can no longer rev from idle and it bogs down. I twist the throttle and it kind of just chugs and sounds sickly, it will then die if I dont clutch in and rev it back up to 4K+. On decel, it will backfire if I let it drop below ~4.5K.

So, in summary, it runs decent at idle with no load. Runs great above ~5K with load or without. It is not able to pick up rpms from below ~4K under load, I will twist the throttle and nothing happens and it just sort of runs crappier. It will die if I bog it down under load and then clutch in and release the throttle. The WD40 vacuum leak test did not reveal anything obvious, but then it seems to run OK unloaded anyway. Running lean? Running rich? Flooding? Leaks? What are your thoughts?