Fast/idle when warm

[darkdev]

How dee thee fella-me-lads. I was hoping that someone would be kind enough to help me out...

My symptoms:

1. It can take 15-20 minutes for my engine to be 'warm' enough NOT to stall without the choke on. All the other bikes I've had could start without choke on a warmish day at least. Is this a common GS thing? Why is it a common GS thing?

2. After the 15-20 minutes of erratic and 'rich', choked miles; once choke is removed the revs still have problems in dropping from 3500-4000 rpm to the preferred 1200 rpm idle speed. In fact, the only way it drops, is if I slow the engine speed with the brakes whilst riding. I've never known a bike to be so sloppy to return to idle when the throttle is released.

3. When idling, the engine can do about 30 revolutions, and then it sounds like a cylinder just mis-fired, almost stalling it, obviously.

Generally, the bike's running like a bag of crap.

What I know:

1. Throttle cable is new, freeplay is correct
2. Carbs are syncronised (at 3000rpm, warm)
3. Engine idle speed is set at 1200rpm
4. Timing is spot-on
5. Valve clearances are set correctly
6. Spark plugs are new
7. Cam chain tensioner is working properly

Why the hell is it doing this?! I had a 500 mile-round trip on it last week, and it bugged the crap out of me everytime I came to lights, roundabouts (Europe) and such. Don't even mention 'slow-control' to me; that thing had be almost into the back of some poor old dear in her 1950s 'banger'. I mean, when you rev a bike, it should rev, then instantly drop the revs back down to idle in less than a second - in my opinion of course. What are your thoughts?

I want it to be fixed, because I don't want to sell it, but if it persists, I'll need to change it within the month. Probably for an SV650, CB600 or similar. And I wanted to give it the TCP elliptical make-over. I've already gone to the trouble of having the frame completely repainted, charcoal grey. Looks proper nice with the orange/black model.

[Wrecent_Wryder]

It's not normal for the GS at all. The GS is a little cold-blooded, as you might expect for a low displacement air-cooled engine (surface-to-volume ratio and all that), but what you're describing is not right. I usually use a little choke even on a warm day, but "warmup" (to the point where it will idle without the choke) is maybe 3-4 minutes max even on a cold day.

Sounds to me like it's very lean, and the first thing I'd suspect is a vacuum leak. I'd check carb boots for tightness and condition,  Check the vacuum hose from the carb to the petcock diaphragm, check to see that the corresponding take-off is capped on the other carb. Check your float levels while you're at it... what year is it? Have the carbs been apart (there are these tiny o-rings...)?

Bottom line, it's not supposed to be that way, you need to find the problem.

[darkdev]

It's a 1997 with near 39k on it now. To my knowledge - I certainly have not done it - the carbs have not been split.

Cheers guy; I'll get 'on the mofo' today, strip the mikuni bst33 down and such. Should it be the case that I can't find anything wrong with the carb, should I worry it could be a cracked block or dodgy gasket somewhere else?

[Wrecent_Wryder]

Should it be the case that I can't find anything wrong with the carb, should I worry it could be a cracked block or dodgy gasket somewhere else?

Nothing's impossible, of course, but it's not likely, guessing from the symptoms you've described. Over half of the problems people report with the GS500 are carburetor related. I don't think I've heard of a cracked block yet.

[darkdev]

Well blow me out a nugget of confusion and tow the line to smackville... don't know where I'm going with that, as neither do you most probably.

Right, so I've replaced the gasket between the inlet manifold and the rubbers from the back of the carb. In addition to this, I've stripped the carb down, cleaned it, rebuilt it, adjusted the float height to perfection (or near enough, I mean who can measure 14.6mm precisely without lasers?) I've also flushed/blown out the fuel/vacuum pipes, done the same to the main fuel chicken, fitted an inline fuel filter and after some more consciencious brain thingies; trimmed the ends of the HT cables for a better connection at either end.

All carb gaskets, o-rings and diaphragms are new and tight sealed, plugs are new, battery is fully charged and still it's running like a bag of peas that entered into the egg and spoon race: unable to perform like the broken monkey it is... or bag of peas.

Should I save all the good bits, set fire to it on a cliff and get a new bike? Should I have a go at a Honda? What does y'all reckon to the Yamaha FZR600? I quite like the idea of a little bit of front fairing to save me from the wind at 90 down the motorway

[scratch]

Float height is too low; set it to 13mm or less (12mm is perfectly acceptable, that is the level that I am currently running at).

Set the idle to 1200-1300 after a good 15-20 minute ride.  Use the throttle to keep the rpm's up when cold, and in the morning(s).  Nature of the beast.

You're running too lean.

And, the GS is not like all other bikes.