Hi, appologies for what looks like an essay below, but I have tried to give an as detailed account of my problem as much as possible, to assist any advice you may be able to offer...

Im looking for some help / guidance on diagnosing a problem Ive got with my GS500 which has only occurred in the last two days or so.

Firstly the bike its a 1998 GS500e with just under 37k on the clock, owned just over six months and it came with a stack of history so has been looked after.

Symptoms, on my way back from the MOT (which it passed) I noticed it was idling a little low when stationery, so I thought maybe the garage had tinkered with this, so I adjusted it so it was idling at just over 1000rpm. Thought no more of this.

Following day, after I had been riding for about 30 minutes, so engine was at full working temperature, It stalled twice when trying to pull off from a standstill, thinking about it, it was like it was bogging down when opening the throttle in low revs. After these two occasions, normal service was resumed.

Today, on my commute to work, had to switch to the reserve tank, nothing unusual there, however, I think I switched it a little too far and left it on prime all day....lost some fuel...had some trouble starting the bike after this point which I guess could have been expected as it had been on prime all day.

Once I got it going, filled up the tank. It did seem a little lumpy, seemed as though it was missing now and then, I dont think it was but thats how it felt when accelerating, also noticed that it had developed a bit of a backfire when blipping the throttle at low revs...that was new.

Just come in from inspecting the spark plugs and the one is all coked up and the other is bright white, so one cylinder is obviously rich, and the other lean.

Does this sounds like this could be the cause of the problems I have just described, or should I be looking at something else.

Any advice on how to rectify the mixture issue would be greatly appreciated.

Thanks All

If it's got two carbs, it's almost certainly a float valve problem on the one that's sooted up. Sometimes, there is a bit of sludge or grit stuck in the float valve or it could be a bit worn. Drain the bowl a couple of times or remove the carb, strip and clean. If the valve is sticking, fuel just overfills the bowl, enriching the mixture on that cylinder, causing rich running and misfires/backfires etc.
Mike

I agree; sounds like a carb prob.

Also check for air leaks on the white plugged side as this could give you the same set of circumstances.

Thanks for all the replies, Ive just ordered the workshop manual and am going to strip and clean the carb, see how it goes then? Im pretty handy as far as maintenance goes so not affraid to tackle this, will the haynes manual provide sufficient information for me to do this.

Are there any things likely to need replacing which I could buy prior to stripping it down or should I just suck it and see so to speak.

To pick up on the air leak suggestion, I was going to update my post a little.

Started the bike up from cold this morning, and heard what I can only describe as a spitting noise coming from by the carbs, it was intermittent and happened only a handful of times, didnt affect the idle or anything. Could this be the signs of an air leak, maybe caused by head gasket or something.

Id imagine an air leak would be hard to track down, any tips on a good place to start would be much appreciated.

Thanks for all your help so far with this, much appreciated.

One way of checking for an air leak is start her up and spray some WD40 where the sound appears to be coming from - if the engine note changes there's a leak.

On an older bike this can be quite common when the carb rubbers (inlet rubbers) get old and hard, I had this problem on my Superdream. Can't remember what was done to sort it as it wasn't me that did it but I don't remeber buying new rubbers??

Thanks for all your replys, just thought Id give an update as I have now fixed the problem, so for those that are interested:

Started the bike up yesterday with the choke on, turned the choke off after only about 30 seconds, expecting the engine to stall...to my suprise, it didnt, it ran fine. As I wasnt intending to use it over the weekend, thought Id leve it go stone cold and try again in the morning to start it up, this time, without the choke.

Went out this morning and she started first time without the choke on. This led me to believe it was more of an air leak than mixture issue.

So, pulled the bike out of the garage, and into the daylight. Left the engine running and could feel some air blowing from the top of the carb, but couldnt quite pinpoint where it was coming from. I happend to look at the carbs from the other side of the engine and found what I can only describe as a rubber cap, about 2cm long and the same diamter as a biro.

This soon led me to think that it had come off the carbs somewhere and was some kind of air plug.

From looking at the carbs both sides, I established that this "Plug, Cap" was off the black cover on the top of the carb, it has a sort of breather pipe on it, not entirely sure as to why, but by putting the cap back in place, the engine note changed instantly and no more back bire.....

Gave the plugs a quick clean with a wire brush and she seems to be running like a dream now.....

Think I'll give her a full service next month and change all the filters, oil, plugs etc, then see how the plugs are after a few hundred miles and see whether the mixture problem has been resolved by fixing this airleak before I think about cleaning the carbs....

Thanks All

Sounds like the cover for the stub that you would put the gauges to to balance the carbs to me.

I agree with the above. It sounds like the vacuum pipe to attach the vacuum gauge to when you balance the carbs. If left open the carb would pull too much air and weaken the mixture - perfect setup for backfiring and dodgy slow running.