Hi everyone,
I have been getting my old '93 GS500E back on the road (had it since new)  but I can't fix my latest problem although after reading about 50+ posts, I suspect it is something in the carbs or possibly my fuel addative. Anyway, I de-rusted the gas tank, new air filter and plugs. I put in fresh gas and added some fuel system cleaner. I tried to start it and it cranked right up. It ran real smooth at first but I heard a pulsating hissing sound so I checked all the vacuum and fuel lines using the GStwins diagram. I found that the vac line from the frame petcock was off so I put it back on. The bike still starts cold immediately with the choke on but it doesn't idle right anymore. It idles then revs up to like 4-6K then back down, then up, then down, up etc.... It doesn't stall and I can drive it but it constantly does this up and down idle. Also, even when warm  the choke cannot be closed fully. If I try to close it more than half the r's just decrease and it dies. Final symptom, when it is running and I try to give it throttle, all I have to do is just a quick twist on/off and the engine (after a short hesitation) will rev way up to like 5K before going back down to the fluctuating idle. Oh, when at the low idle in the fluctuation it is at about 12-1500rpm.
Any ideas on why it is doing this and what I have to do to get it idling smoothly?? I am hoping to get a few rides in this year yet.

Tomorrow I plan on checking the choke cable to make sure it is function right, draining out the gas with the addative and putting in fresh stuff again. Can anyone narrow down my search for a cure?

Thanks very much.

To me the symptoms sound like a lean mixture.

I would check the fuel supply, air supply, and look for vacuum leaks.

Sounds like a lean mixture problem like said abive or dirty float needles and float bowls.  I would check your float height with the tube method everyone uses here.  If it is low then there is your lean mixture problem.  Good luck.  I'll check up on here to see how things work out.

Thanks for the advice. Today I checked the float levels by the tube method and they were equal height at about 2mm above the bowl level so they are ok. I pulled the plugs and both look normal by the hayes picture. The choke is moving normally. I reset the idle speed screw to 3 turns out. All the vac hoses seem to be connected and they are like new so I don't think any of them are leaking besides that I don't hear any air like I did when the vac hose was off the petcock.

I started up and she ran rough but level for like 15 minutes (warmed) but then started going up and down between 1300-3000.    I lowered the choke and she settled back in at 1300. I tried giving some throttle and it immediately just bogged down and died. Restarted and tried again with small quick throttle burst and it started to rev to 5k but then with no warning it just went from 5k -0 and died. When I started it again (without touching the throttle) it jumped right back up to 5k and then died. Restarted and it went to about 3k and then settled back down at 1300 for another 15 minn at half choke. I tried to give it throttle and just hesitated and died. Now it is really warmed so it shouldn't need cholde but it needs half or it just spins and won't start and giving throttle while trying to start doen't help.  So I give it half choke and it turns over and revs to 4k and dies 2x.

I am totally bummed.  Any advice is GREATLY appreciated.

Check your carb boots (manifolds) for cracks or leaks. Try spraying some starting fluid or carb cleaner on them while it's running, and if the engine speed changes, then you have a leak.

Did you put that whole bottle of carb cleaner in there? any more than 1/4 bottle would be too much and could cause problems. Drain the gas and put it in your car, if you haven't already.

Idling for 15 minutes could overheat the engine, because there is no air flowing over the thing. This could cause some problems. If you have a fan, aim that at the engine while idling it for a while.

Good luck 

No cracks or leaks visible. They look like new. I sprayed starting fluid on them as suggested but she just kept idling along at about 13-1500rpm so no leaks there. It seems to idle better when cold/cool and deteriorates as the engine warms but you can't even touch the throttle when cold without a stall whereas when warm you can sometimes get a ride in.

No, I put it in yeaterday afternoon and didn't use the whole bottle; only about 1/3-1/2 (more than I wanted to but I didn't measure it out like I should have) but I figured it was too much and drained it back out today. Yup, I put it in my car. 4.5 gals. of gas is too expensive to waste.

Yeah, unlike my Nighthawk that prefers to idle a while before takeoff, I noticed that the GS gets way hot when just idling so I give it breaks in between tests. Or as I did yesterday, I take it for a spin up and down our road. Unfortunately, it isn't running as well today as it did yesterday so no rides. Maybe a clue! Today is is cold and rainy here in PA but yesterday it was warm and clear. However, as I said the plugs are firing fine (I did a spark test).

I may not have said, I did manage to ride it yesterday up and down the road for a total of 1.1miles. It stalled a few times, bucked some doing U-turns, and you could feel the up and down revving of the engine when coasting but the more I drove the better she seemed. Today though....phbttttttt

Any other ideas before I go insane?

I'm still leaning towards a lean situation.  As you said it will idle back down if you give it some choke.  The mixture becomes rich when the choke is applied.  I don't know if you have ever torn apart carbs or not, but your mixture screws might be dirty.  This would inhibit the flow of fuel/air to the cylinders.  I would just do a tear down and cleaning of the carbs.  This solved the problem I had which was very similar to yours. 

Alex

"It ran real smooth at first but I heard a pulsating hissing sound so I checked all the vacuum and fuel lines using the GStwins diagram. I found that the vac line from the frame petcock was off so I put it back on. The bike still starts cold immediately with the choke on but it doesn't idle right anymore."

It ran fine before you put the vac line on and didn't after.

How many vac lines do you have?

Make sure that line is on there correctly. Where does the other end go?

You could disconnect it again and put petcock on prim and see what it does. 

Good luck.

Quote from: Toledo Jim on October 21, 2006, 12:19:21 AM
"It ran real smooth at first but I heard a pulsating hissing sound so I checked all the vacuum and fuel lines using the GStwins diagram. I found that the vac line from the frame petcock was off so I put it back on. ...........................

This behavior is stange because with the petcock vacuum line off the fuel flow to the carbs is off (unless you originally had the fuel petcock set to prime).

Check for tears in the slide diaphragm, and make sure the tiny o-ring under each carb top is present and in good condition.  Also, I think your float level is too high.  Inspect the float needles for wear around the tips.

Hello all,

I seem to have the same problem with my bike: starts, idle fluctuates, when I give it gas (throttle) it bogs down and dies.  I see that many of you think it might be due to one of these:

1 lack of proper seal
2 too lean
3 dirty carb

how can I get my bike to run richer?  is there a way to know it is too lean (measurable, I dont know enough about bikes to know just by sound alone)? Meth3 let me know how your problem turns out,  good luck and thanks for any advice in advance

My bike sat for a couple of months while I was working on the suspension and when I went to fire it up I had the same / similar problem.  It would start and idle ok but opening the throttle caused the engine to die.  I got the carbs off today and found the problem. 

The emulsion tube (also referred to the needle jet in the manual) in each carb had become clogged with funky gas.  About half of the holes in the tubes were totally blocked.  When the throttle was opened, and the carb diaphragm lifts the slider, gas could not pass through the emulsion tube and so the engine died.  Clearing the blockage fixed it right up. 

Maybe you have the same problem?  I can walk you through disassembling the carbs and checking the necessary passages.  Drop me an e-mail: mike_manders@hotmail.com

Hello again. Wow, A lot of posts since last night. Anyway, I followed a few of the new advices.

Didn't get to do much today but I checked the petcock vacuum hose that had come off and it was secure on both ends. The other end goes up between the carbs and ends going into the left side. I checked the Haynes pic again and this is where it should go. I took off the hose again and put the switch to prime and had the same results as before - idled smooth but low rpms (1000). Put the hose back on and switched to ON and the R's increased and she started to do mild fluctuations. Tried to throttle a bit and Blahh. SO nothing new there.

It seems the consensus is rebuild the carbs. I was hoping it wouldn't come to that but with the rust I found in the tank, it is not a total surprise.  Last time it was done by the dealer as part of maintenance (years ago) so I have never had to do it. I am not a bike  mechanic but I may try it. I may be contacting you mike for some guidance if I start this project but it wouldn't happen until at least Thursday.

So, an a 1-10 scale...how difficult is a carb rebuild. I read the sites step-by-step but I have been told that a rebuild is more than just putting in new parts and putting it back together. Any thoughts on what this or if I should try it solo?

Thanks alot!

With 1 being "no harder than filling it with gas" and 10 being, "damn, I wish I'd paid the Suzukistealer $xxx.00 to do this for me  ,"  I'd say that a carb rebuild falls in the 5-6 range.

A few lame and probably obvious tips:
- get the right manual for your carbs.  The Clymer does not show the right parts in the right places for the carbs on my '02, manufactured in Aug '01
- take apart and re-assemble only one carb at a time
- be really nerdy about keeping your workspace clean and well-lit
- be very careful where you put parts during dissasembly
- buy and set out your replacement parts before your start. (this is tricky, as there does not seem to be a complete rebuild kit for these carbs - who's to know if you need $20 in parts or $60?)
- take your time.
- remember that carbs are very precise devices - almost all parts of a carb are very easy to permanently damage
- document what jets you've got in there.

Good luck, let us know if it solves your troubles!

Quote from: meth3 on October 21, 2006, 03:27:30 PM--snip-- I took off the hose again and put the switch to prime and had the same results as before - idled smooth but low rpms (1000). Put the hose back on and switched to ON and the R's increased and she started to do mild fluctuations. Tried to throttle a bit and Blahh. SO nothing new there. --snip--

Keep it simple until you can't.

I still think it has something to do with the petcock / vac line. (Since you said the problem was first noticed when you hooked up the vac line to the petcock.)

If the bike idles smooth in prime, and has problems in on or res, then that problem should be addressed before tearing other parts of the bike apart. (Any other problems can be worked on after you figure that out.)

Have you tried to ride the bike with petcock on prime?

Jim

Well, with the vac line off it idles nice but can not take any throttle so it can't be driven at all. As soon as it is put back on, the whole sound of the idle changes and roughens as I said previously but she does take a little throttle once warm if coaxed gently and can be "ridden".

I did notice something wierd which I forgot to mention but was reminded by my spouse as we discussed whether to pay our mechaninc the $100 he quoted for a rebuild or tackle it myself... When I was riding up and down the street it stalled in both U-turns and was bucky on the staright but when I drove up the incline to put it away (about 120ft.), she seemed to rise to the task. After a couple bucks she seemed to grab hold and took off like nothing was wrong but as I slowed to a stop on the level to open the door, it just lost it again and stalled before I had a chance to hit the kill.

I have been working on the bike for about 4 weeks now and am seriously considering just handing it over to the mechanic.  I trust him but I just hate to hand over the bike with a list of symptoms and say find what's wrong and fix it. I think ya'all can see why.

I will take your advice Jim and first pull the petcock and the vac line totally off and look for clogs or leaks. For the tube = I will block one end, submerge it, and force air into the other end. Any leaks should give bubbles. (Before being chastized  - I know it has to be totally dry before re-install). The petcock, I will have to see once I have it off. Maybe I will get lucky 

It's just your carbs man, pull 'em and clean 'em.  There's nothing to it.  It's harder to get them off the bike than it is to disassemble and rebuild them.

I've had lots of carb issues too. Here's what I've found out about them...

They're not hard to rebuild, just take your time.
You haven't mentioned what altitude you're running at. If you're much above sea level, you're going to have air issues because of a lack of oxygen.
What air filter are you using? If it's different than stock (like my K&N), you're going to have air issues--they draw air better than stock. Combined with stock jetting & you have issues.
As above, make sure all your gaskets, rings, & such are in good order. +1 on the manifold boots.
And when you're done--get your carbs synced! I can't stress that enough. Thought mine were fine, then I got them synced. Turns out one side was all F'ed up!

I've had huge carb issues. Turned out to be a combination of things--bad gas tank letting garbage in, great air filter & stock jets, bad cap on one carb, and on and on.

anyone still have emulsion tubes?