So I picked up this 1989 gem and refurbished the whole thing. It was running perfect and I put it up for sale. A buyer came to check out the bike and together we had a look, even took off the tank to show the throttle slide condition.
Things went wrong from there. Tank fuel petcock started to leak so I had to replace that one. Worse: After putting the (right) carburetor cover and the tank back on the bike wouldn't idle properly. It turns out the fuel isn't running through and I do not know why. Here's a recap of things I did and things that happened:
- Acquired the bike and cleaned the carburetors and replaced all O-rings.
- Installed new throttle needles
- float needles looked fine
- throttle slides, slide guides and membranes are fine
- replaced all the fuel hoses and vacuum hose
- cleaned out the tank, removed all rust and applied an epoxy coating
- added a fuel filter to make sure everything stays clean despite the coating in the tank. Sidenote; I own another GS500 (1996) that has been running perfect with this setup and exactly the same filter
When the buyer visited:
- took off the tank and damaged the tank fuel petcock
- removed the right side carburetor cover to show slide guide/throttle needle/membrane status
- after putting everything back together the bike idles unstable and stalls at traffic lights
What I did since then:
- took apart the carburetors again and once again cleaned them even though they already were
- again replaced all o-rings, this time with this official GS500 carb repair kit. Also installed new float needles and seats. I did not forget to replace the pilot screw o-ring.
- made a small adjustment to the float height as it seemed like a little too high (it is now just above the float bowl)
- took apart the normal fuel petcock and cleaned it. There was a flake of rubber (fuel hose) inside.
- again replaced fuel hoses
- removed the air from the fuel petcock and fuel filter
Still nothing. A few kilometers into the ride the fuel filter is empty. The engine holds back a little due to fuel starvation. When opening throttle 100% on the highway it first holds back a bit then very slowly starts to climb in speed. When parking the bike it takes about 2 minutes before the fuel filter fills up halfway.
When opening the float bowl taps the fuel runs through freely. When taking the hose off the end of the fuel filter it runs out like crazy. Fuel petcocks are clean and fuel can pass through freely, the problem is there at all petcock positions (On/Res/PRI). Float height is good. I can think of no single reason why the fuel is not running through properly and yet it doesn't. It's not the fuel cap because there is no change when I leave it open. Not a clue where the air in the fuel filter comes from. Air goes up yet the filter is in a low position.
why why WHY??? It ran perfectly fine before I showed the bike to the buyer. I don't recall doing anything wrong and I have checked everything 10 times already.
(https://i.imgur.com/ELaAq5s.jpg)
Sounds to me like the filter is restricting fuel flow. Either that, or the screen in the tank is clogged.
Quote from: qcbaker on August 09, 2017, 11:51:04 AM
Sounds to me like the filter is restricting fuel flow. Either that, or the screen in the tank is clogged.
Both not the case. I took the fuel petcock from my other GS500. Its clean and fuel runs through fine. The fuel filter is not the problem either, put the petcock on PRI and take off the exit-hose of the filter: you will drown in fuel. Add the fact that before the buyer came along the bike ran perfectly well with this setup and as mentioned my other GS500 has been running like this for years.
I know you're convinced it's not the fuel filter but what would it hurt to bypass it just in case? It's the most likely cause at this point.
Other thing would be if the air vent in the fuel tank is clogged so air can't get back into the tank (will prevent fuel from flowing) or maybe the fuel hose is actually hooked to the upper "T" rather than where it should be, and you are only accidentally getting fuel?
I don't know how you have determined that "fuel is not running". If you put it on PRI and pull the fuel line from the carbs at the "T", does fuel flow out? Put a drain line on the carb bowl drain, put the petcock on PRI then open the bowl drain screw, does fuel flow out? Does it keep flowing even when you've drained enough to drain the entire bowl?
I'd have to guess from what you describe doing that the problem actually is that the slide on the carb you opened up to show the buyer is not coming up. Diaphram is pinched or damaged or has a hole in it, etc. Likely was damaged or put together wrong when you pulled the cap. Otherwise there may be a big vacuum leak on the top side of the diaphragm causing it to not come up. Anyway, since that's the last thing you touched before it all went nuts, then that's the most likely cause IME. Maybe one or the other diaphragm came into contact with carb cleaner and has a hole melted in it? Maybe there's a gap in the rim of the diaphragm cover causing it to leak air in so no vacuum can be developed sufficient to raise the slide? Maybe the needle is stuck, misaligned with the jet, etc.? Pull the airbox and observe the slides while running the bike, opening the throttle, make sure they both go up in concert.
Otherwise you might have developed a clogged passageway to the pilot jet, it's a tiny thing and easily gets clogged. Worth checking.
Quote from: kapiteinkoek on August 09, 2017, 11:55:45 AM
The fuel filter is not the problem
I mean, you say that but you also say that the fuel filter gets empty when riding and is not filling up quickly when the bike is parked. That sounds like a fuel filter restricting the fuel flow.
You've also said the problem persists when the frame petcock is on PRI, so I doubt it's related to incorrectly routed vacuum line or faulty frame petcock. Remove the fuel filter and run a fuel line directly from the tank petcock to the frame petcock and see if the bike improves.
Quote from: mr72 on August 09, 2017, 12:05:56 PM
...
Other thing would be if the air vent in the fuel tank is clogged so air can't get back into the tank (will prevent fuel from flowing) or maybe the fuel hose is actually hooked to the upper "T" rather than where it should be, and you are only accidentally getting fuel?
This is also a possibility.
Quote from: mr72 on August 09, 2017, 12:05:56 PM
I'd have to guess from what you describe doing that the problem actually is that the slide on the carb you opened up to show the buyer is not coming up. Diaphram is pinched or damaged or has a hole in it, etc. Likely was damaged or put together wrong when you pulled the cap. Otherwise there may be a big vacuum leak on the top side of the diaphragm causing it to not come up. Anyway, since that's the last thing you touched before it all went nuts, then that's the most likely cause IME. Maybe one or the other diaphragm came into contact with carb cleaner and has a hole melted in it? Maybe there's a gap in the rim of the diaphragm cover causing it to leak air in so no vacuum can be developed sufficient to raise the slide? Maybe the needle is stuck, misaligned with the jet, etc.? Pull the airbox and observe the slides while running the bike, opening the throttle, make sure they both go up in concert.
This is also a strong possibility. If it isn't the fuel filter, its probably something along these lines.
Quote from: mr72 on August 09, 2017, 12:05:56 PM
I know you're convinced it's not the fuel filter but what would it hurt to bypass it just in case? It's the most likely cause at this point.
Other thing would be if the air vent in the fuel tank is clogged so air can't get back into the tank (will prevent fuel from flowing) or maybe the fuel hose is actually hooked to the upper "T" rather than where it should be, and you are only accidentally getting fuel?
I don't know how you have determined that "fuel is not running". If you put it on PRI and pull the fuel line from the carbs at the "T", does fuel flow out? Put a drain line on the carb bowl drain, put the petcock on PRI then open the bowl drain screw, does fuel flow out? Does it keep flowing even when you've drained enough to drain the entire bowl?
I'd have to guess from what you describe doing that the problem actually is that the slide on the carb you opened up to show the buyer is not coming up. Diaphram is pinched or damaged or has a hole in it, etc. Likely was damaged or put together wrong when you pulled the cap. Otherwise there may be a big vacuum leak on the top side of the diaphragm causing it to not come up. Anyway, since that's the last thing you touched before it all went nuts, then that's the most likely cause IME. Maybe one or the other diaphragm came into contact with carb cleaner and has a hole melted in it? Maybe there's a gap in the rim of the diaphragm cover causing it to leak air in so no vacuum can be developed sufficient to raise the slide? Maybe the needle is stuck, misaligned with the jet, etc.? Pull the airbox and observe the slides while running the bike, opening the throttle, make sure they both go up in concert.
Otherwise you might have developed a clogged passageway to the pilot jet, it's a tiny thing and easily gets clogged. Worth checking.
I'll try removing the filter but I still highly doubt that this is the problem. Like I said pull the hose -after the filter or at the carburetor lower T - and the fuel gushes through the filter.
Air vent isn't clogged, tried running it with the fuel cap open. Fuel hose is connected to the lower T, upper T is the stock overflow hose going nowhere.
Put the fuel petcock on PRI and open the float bowl tap and it will keep flowing steadily. You can drain the tank through it if you like. It comes out easily at a rate faster than the bike can consume it at topspeed.
Diaphragm is fine, checked it twice. Carb slide is fine, checked it twice. Vacuum leak isn't there, have checked it all thoroughly. Take out the filter and you can watch the slides open up with the throttle. Needles aren't stuck, they are also new. Jets are fine, checked them twice. Pilot jet is fine, checked it twice.
Quote from: qcbaker on August 09, 2017, 12:11:43 PM
Quote from: kapiteinkoek on August 09, 2017, 11:55:45 AM
The fuel filter is not the problem
You've also said the problem persists when the frame petcock is on PRI, so I doubt it's related to incorrectly routed vacuum line or faulty frame petcock. Remove the fuel filter and run a fuel line directly from the tank petcock to the frame petcock and see if the bike improves.
I will try it without the filter but I will tell you now, it's not going to work.
You said you damaged and then later replaced the tank petcock, right? Perhaps the tank petcock you replaced it with is somehow faulty. Or, again, the screen in the tank could be clogged with something (rust, old fuel gunk, etc)
Quote from: qcbaker on August 09, 2017, 12:36:40 PM
You said you damaged and then later replaced the tank petcock, right? Perhaps the tank petcock you replaced it with is somehow faulty. Or, again, the screen in the tank could be clogged with something (rust, old fuel gunk, etc)
As stated in the opening post, the fuel tank is absolutely clean. I removed all rust from the tank and coated it with epoxy. This thing is spotless and it will be spotless for the coming decade. The petcock screen is as clean as it gets as well.
(https://s11.postimg.org/omg0dy1tv/tank2.jpg)
All I have to say is this: you say there is something wrong with the way it runs (which you think is "fuel not running through" although I think it's pretty clear this is not the issue), so you have likely overlooked something.
Have you checked the plugs?
Anyway, I think the idle problem and the fuel starvation problem are likely two different problems.
Now re-reading your initial post, I suggest there must be a way air is getting into the fuel line to allow the fuel filter to be not-full. It could be as simple as a leak in the fuel line allowing air to be sucked in. Gravity and hydraulics should not allow the fuel filter to ever have air in it once it has been bled off. Even a clogged fuel filter would still be full of fuel, it just wouldn't drain quickly enough. Air is leaking in somewhere. Maybe that vent/overflow hose you say has nothing connected to it should have something connected to it and routed towards the rear of the bike so high-pressure air doesn't push into the carbs. You know what pushes fuel into the jets is air pressure in the top of the carb bowl, and it is a delicate balance that is easily upset by addition of pressure on the supply side.
Quote from: mr72 on August 09, 2017, 01:59:12 PM
All I have to say is this: you say there is something wrong with the way it runs (which you think is "fuel not running through" although I think it's pretty clear this is not the issue), so you have likely overlooked something.
Have you checked the plugs?
Anyway, I think the idle problem and the fuel starvation problem are likely two different problems.
Now re-reading your initial post, I suggest there must be a way air is getting into the fuel line to allow the fuel filter to be not-full. It could be as simple as a leak in the fuel line allowing air to be sucked in. Gravity and hydraulics should not allow the fuel filter to ever have air in it once it has been bled off. Even a clogged fuel filter would still be full of fuel, it just wouldn't drain quickly enough. Air is leaking in somewhere. Maybe that vent/overflow hose you say has nothing connected to it should have something connected to it and routed towards the rear of the bike so high-pressure air doesn't push into the carbs. You know what pushes fuel into the jets is air pressure in the top of the carb bowl, and it is a delicate balance that is easily upset by addition of pressure on the supply side.
Plugs are new and work fine. It makes no sense for air to be 'sucked in'. There isn't any worthy sucking action going on in the carburetor on the fuel intake and the GS500 fuel flow rate isn't high enough to suck something in with it. Since the whole system is pressurised by the fuel several inches above the system any 'air leak' in the fuel system means fuel would be coming out. There are no leaks. The vent hose should have nothing connected and is routed towards the rear. Fuel isn't pushed in the jets, it is rather the under pressure due to the venturi effect that sucks it through.
It makes no sense to me at all that air is ending up in the filter after I have flooded it/let it escape. Wherever it comes from the air is traveling down in a barely moving fuel flow. I have considered vapour lock but the hoses or filter aren't getting that hot (not actually in contact with the engine). It didn't happen before either nor is it happening on my other bike.
Sounds like you have everything figured out then. :icon_rolleyes:
Good luck.
[You might actually be mistaken about one or more of your assumptions... it happens sometimes... ]
Sure I can be wrong. But let's say there is significant sucking going on wherever in the system, enough to pull air in. If the bike isn't running there is no sucking action but the leak would still be there. The system would be leaking fuel out as it is under pressure by gravity fed fuel from the tank up top.
There is no fuel leaking when the bike is running or not running.
-edit
I removed the fuel filter, nothing changed. This thing is driving me nuts :dunno_black:
While the bike is running (assuming it will at least idle, even if erratically) use a spray bottle to spray water (not carb cleaner, not brake fluid, specifically water) onto the carbs. If the idle drops or the bike stalls, you know you have a vacuum leak somewhere in the carbs. If there's no change, I'm not sure what to tell you. I don't know where else air could be entering the system.
I have a good spray so I will try water
Quote from: kapiteinkoek on August 09, 2017, 02:37:11 PM
let's say there is significant sucking going on wherever in the system, enough to pull air in.
That's "vacuum"
Quote
If the bike isn't running there is no sucking action but the leak would still be there. The system would be leaking fuel out as it is under pressure by gravity fed fuel from the tank up top.
This theory isn't 100% sound. Suffice to say there are plenty of ways for air to get in through a vacuum leak that won't manifest as leaking fuel when the bike is off. Fuel is not air and atmospheric fuel pressure is not engine vacuum. A leaking petcock is a perfect example of how air would get in when the petcock is open and fuel wouldn't necessarily leak when it's closed. This isn't the only example. But regardless air IS getting in so you need to allow a theory by which the observed reality is possible.
Quote from: mr72 on August 10, 2017, 06:13:24 AM
Quote from: kapiteinkoek on August 09, 2017, 02:37:11 PM
If the bike isn't running there is no sucking action but the leak would still be there. The system would be leaking fuel out as it is under pressure by gravity fed fuel from the tank up top.
This theory isn't 100% sound. Suffice to say there are plenty of ways for air to get in through a vacuum leak that won't manifest as leaking fuel when the bike is off. Fuel is not air and atmospheric fuel pressure is not engine vacuum. A leaking petcock is a perfect example of how air would get in when the petcock is open and fuel wouldn't necessarily leak when it's closed. This isn't the only example. But regardless air IS getting in so you need to allow a theory by which the observed reality is possible.
This is was sort of the line of thinking I had when I originally suggested the possibility that the tank petcock that the OP replaced may be faulty. But thinking back, I don't believe the tank petcock is vacuum actuated, is it? So if it were a faulty petcock, I think it would have to be the frame petcock that is failing.
Tank fuel petcock is not vacuum actuated. The normal petcock is and I have opened and cleaned it out. There was a flake of rubber in it that probably fell in when I changed the tank petcock. I figured this would be the problem but nothing changed after taking it out. I have tried running it without vacuum hose, that is capped off the carburetor vacuum port to exclude a petcock vacuum leak. Unfortunately this is not the case either. A waterspray doesn't do anything either.
I know this diagram is in german, but the color coded lines are a good way to visualize which lines should be where. Go ahead and double check them, even if youre "sure" theyre right:
(http://gs-500.info/images/thumb/b/b2/Image004.jpg/500px-Image004.jpg)
Here's an english version so you know what's what as well:
(http://www.gstwin.com/images/how_to/fuel%20hose/www_gs500_de_HoseRouting.jpg)
You could also disconnect the outlet hose from the frame petcock and feed fuel manually using a funnel or someting. This would basically simulate the petcock's PRI function and if the engine runs normally when doing this, you would know the problem lies with the frame petcock.