Some background info first, followed by questions.

Background info

My girlfriend bought a '96 GS500 (CA bike) about 1.5 years ago and only rode it a handful of times. It has 27,000 miles on it. The bike had been sitting for a while and I decided to get it running again. While changing the oil I noticed that there was gas in it, so I decided to rebuild the carburetors. While disassembling the carbs I stripped the slot on one of the pilot jets and got a replacement from bikebandit. After cleaning the carbs and installing new o-rings and float valves I bench-synchronized them and set the pilot screws to 2 1/8 turns out (I'm at sea level.) I don't know whether the valves were adjusted.

The bike starts OK, but doesn't want to idle without choke. It doesn't hang up when revving with throttle open 1/2 way, but after I close the throttle, I hear a pop from the exhaust while the RPMs are dropping. After revving the bike I took out the spark plugs and photographed them. One of the spark plugs is blacker and cooler, and the other one is not so black and is too hot to touch.



There is a possibility that the pilot jets are of different sizes ( I didn't compare the numbers on the original pilot jet and the one I got from bikebandit). I also would like to synchronize the carburetors with a yardstick manometer, but I'm having trouble locating the vacuum port on the RH carburetor. I attached a hose to what I thought was a vacuum port (green circle on the photo), but it didn't move the liquid in the manometer.



Questions

Is the vacuum port for RH carburetor visible anywhere on the second photo?

Do any of the symptoms I described indicate a problem with the carburetors? I would appreciate any suggestions on further troubleshooting.



Thanks,

Ilya.

Finally got back to working on this bike. Still cannot get it running properly, but I was able to find the location of the vacuum caps. See the modified photo.

Right carb where you have put that red circle isn't drilled through. Dont try to drill it or put a cap on it.

The bike wont idle without choke. What else did you clean ...

Bike bandit for the stock pilot jet ... you should have asked on this site ... we put 1 size larger pilots which I sell in a pack along with other jets for the setup on your bike. $25 shipped.

Anyway ... you have blocked something. BTW you have vacuum line hooked up right ? Some how its not getting enough gas at idle to run.
Revving before pulling the plugs is a poor way to diagnose the idle mix problem. let it idle for 3-4 mins wihtout choke, dont rev it, and pull the plugs after shutting it off. That way you can read it @ idle.

I'd clean and set the floats right. Synching them is also best done via eyeball not vacuum, and air screws @ 3 is a good starting point, 2 1/8th is the stock setting which is lean.

Cool.
Buddha.

Buddha,

After much fiddling with the carbs, here are the current symptoms:

1) With air screws at 2.6 turns out, after starting without choke, the bike idles for a few seconds and then RPMs rapidly climb. I shut off the bike at this point.

After reading some forum posts, it appears that the float levels are set incorrectly. However, there's no gas draining from the overflow tube. I have pulled the carbs again to adjust the floats and will post the pictures later tonight. I did a blow test, and the float needles are sealing properly. I have a suspicion that the float needles are installed incorrectly on the float tangs.

Quote from: ilya on January 05, 2010, 02:03:44 PM
I have a suspicion that the float needles are installed incorrectly on the float tangs.

Yes im curious which way they go on too... I believe I put them on the same way they came off, but I cant be 100%.

Floats wont cause it to rev up ...
So first off before taking anythign apart, back off the idle screw. Set it where it needs choke for the first 1 minute after cold start. It should rev between 3-4K on the choke. Then when you're taking it off the choke, it should rev 1500 or so, set the idle screw there. Then ride it ... 20 mins of riding later it should be right about that same 1500.

Now if it revs higher as it gets hotter, open the air screw more.

If it will still do that after you get it to ~5 turns on air screw, you need to rejet.

I am assuming your floats and synch are OK, and that is a reasonable assumption, you being able to set the idle etc right indicates they are not too bad.

If you have to remove them off the bike, then check synch and floats, else run em as it is.

Literally if the bike behaves proper at all stages of use, I will leave it be till you have to crack it open again.

For now ... idle screw ... then air screw ... then fiddle the rest.

As it revs up after starting, turn the idle screw out till it settles @ 1500 when its been runnign for 1-2 mins with choke. Go ...

Dont laugh, I just spent 20 mins draining the oil on the bloody savage in the dark and cold (20's and windy ...) ... who's the moron that put the oil drain where you can get a wrench on it only after laying the bike on the right ... man I wanna kill him.

Freezing cold days are golden for working on jetting ... mine (savage) ran without skipping a beat today ... whoo hooo and the xs did that this weekend, a balmy 25 degrees and broke the 35 mark for the high ... booya ...

Cool.
Buddha.

The carbs are now off the bike. I'm attaching a photo of the current position of the float needle. Is it installed correctly?

Buddha, thank you very much for answering my questions about the carbs. I think I'm getting a feeling that I might be able to get the bike running this time around. To answer your questions, when the carbs were on the bike, the idle screw was turned all the way out, so it was not touching the throttle linkage.

Idle screw should be touching the linkage and should be about 1-2 turns open past making contact.

Float looks fine though it could be high for level. May have to set it right. Though a picture is a terrible way to comment on a float. It coule be just fine ... just check it then install it.

Cool.
Buddha.

Quote from: ilya on January 05, 2010, 02:03:44 PM
Buddha,

After much fiddling with the carbs, here are the current symptoms:

1) With air screws at 2.6 turns out, after starting without choke, the bike idles for a few seconds and then RPMs rapidly climb. I shut off the bike at this point.

However - Climbing rpm isn't due to a shut off idle screw ... it will cause it to stall ...
You got somethign else wrong there also.
Vacuum caps or somethign ...
Cool.
Buddha.

During the last couple of weekends I attempted to adjust the valves but ran into some problems. On left cylinder (facing forward), the IN valve gap was at .13mm and EX valve gap was <0.03mm. I was able to set all valve gaps in spec except for left cyl. IN valve. After I put in a thicker shim, the gap has increased tremendously, to the point that it's visible without a feeler gauge. It seems to me that the bucket is not extending all the way. It's possible to rotate the bucket by hand, so it's not stuck.

At this point I'm seriously considering giving up on this GS. I'm reaching limits of my mechanical skills and I have too many other projects at the moment. So if anyone is interested in '96 GS with 27k miles, good tires, straight frame and forks, overhauled carbs, good electrics (as far as I can tell), 1-year old battery that's on Battery Tender, and no rust, please contact me. I can deliver within 100 miles of Los Angeles.

You put in a thicker shim and clearance increased ... OK now you know if the bucket was all the way out before when you measured it ?
Cool.
Buddha.

It was just a guess, based on the fact that previous reading of 0.13mm is just barely out of spec, compared to the wildly out of spec reading that I obtained after the shim change. I think I stopped measuring at 0.7mm.

You think you read the numbers on the shim correctly. BTW you can measure the shim exactly with a micrometer and confirm its size.
BTW If you pull the shim out and put a new shim in based on accurate calculations, I will not bother measuring it till you get it ridden even if it is a few feet. The shim floats on oil and gives you a lower reading than it should have. Like you pull a 260 shim cos its tight and put in 255 and you can have 0 clearance. Oh crap you think and put in a 250, still 0, what ... 245 - 0, 240 -0 ... yea you get the idea. Oil float I call it.
Cool.
Buddha.

Unfortunately I don't have a micrometer, but I did measure the shims with a dial caliper that's accurate to 0.02mm. After replacing each shim I turned the crankshaft several revolutions to squeeze the oil out. Well, I'm going to put the bike back together this weekend and give it a shot. I can't possibly make it any worse .

Hi,

Having a hanging high idle is likely to be caused by extra air coming in somewhere so that the engine runs lean. You said that one spark plug is hotter that the other, so I would check the rubber boots for air leaks in that side.
Also check vacuum seal plugs (the ones you put a green circle around in the first picture) for tiny leaks.