Hello all,

I am a new member to this forum, and have been reading up a lot since getting my gs500.  About 2 months ago now I purchased a 1990 GS500E with 7200 miles on it for my girlfriend to learn to ride on.

Upon getting it, it suffered from what I read is the common fuel starvation problem.  At first the bike would only run decently up to about 55mph (with a slight bog in a roll on), but would pop and spit if attempting to go any faster.  I have since

1) Replaced stock fuel petcock with after market valve (couldn't find a rebuild kit for the original, and didn't think it needed it, as it seems to be fine)
2) cleaned filter in tank
3) rebuilt carbs and wired them out, paying particular interest to the pilot circuit
4) attemped to shim the needle jets with 3x1mm o-rings
5) replaced intake pipes on engine side of carbs, which had a massive crack in them
6) Checked and re-gaged plugs

These changes have made an improvement, namely the intake pipe replacement.  I can now get the bike up to 70mph, but it still suffers from a minor surge.  No back firing this time, but you can feel the bike easing fore and aft.  I have also made sure the vent on the tank is performing as it should (no hissing when opening cap).

So my question is, what could I possibly be missing?  I have in the mail:

a) a set of #40 pilot jets, as well as a set of #42.5
b) 125 main jets

My hope is that by rejetting a size up I can get the bike to running as good as new.  Perhaps this is the solution I need, but I had hoped you guys with more experience than myself on this platform could lend some guidance as to something I may be missing?  The one thing fuel/air related that I have no confirmed is valve clearences all around.  These were supposedly done by the previous owner within the last 500 miles, but I've yet to confirm for myself

Other than at highway speed the bike runs like a dream, and it will run up through the gears all the way up to redline in 4th with no issue.  So I can't figure out why steady-state cruising at highway speeds is an issue. 

Thank you all in advance for any guidance you can give.

Brian

After posting this, I have since received and installed my new jets.  Upon pulling the carbs apart, I found that the original pilot jet was a 40.  So I replaced the mains with 125s, the pilots with 42.5s, and turned the turning screws out 3 turns.

After getting them back on the bike I took it for a cruise and the thing won't run well.  The new jets certainly weren't an improvement over the old jets.  The bike continues to stumble, no at or around 60 mph.  When turning around and heading back on the highway I was able to run the bike up through 5th to ~90mph and it pulled just fine.  But when decelerating, it started to surge again.

I pulled the plugs and they are, as to be expected, quite white.  The bike appears to me to still be running lean.

At this point I am totally stumped.  Could anyone please offer some advise as to what I could be missing?  Just to go over it again, my setup is:

Stock Intake
Stock Exhaust
125 mains
42.5 pilots
3 turns
NGK XS-4163 plugs, properly gapped (my only thought is these may need to be replaced? But they appear brand new)

Thanks in advance

have you read the wii re-jet? maybe you have the wrong size jets? i cant say yes or no for sure, but it'a a possibility

I have read and referenced the wiki a number of times.  Suggested setup for stock intake/exhaust is 40/125.  So if anything I would think with my 42.5/125 I would be a little on the rich side at cruising settings. 

My next step that I haven't tried is to shim the needles again.  Besides that I plan to evaluate whether there are any leaks I missed by spraying the starting fluid around the carb/intake area.

Thanks iclrag and anyone else for guidance

I will offer up my first thoughts - keep in mind they are first thoughts and may hold no substantial credit 
My hopes for these is that they spark something else for you, or others to help. 

After reading your original post, I thought (probably just as you had) that well the carbs aren't getting enough fuel somehow... So I would test via the U-tube method to see how much fuel is actually getting in there to be sure if you haven't already, to get a better idea of where the leaness is coming from.

My next thought was your spark plugs... I'll admit I have limited knowledge of them, so take with a grain of salt... But the XS I thought stood for 'Extreme Sport' .. are they just too hot?  For no more they cost, I would eliminate the variable and go with stock if everything else is, other than your jets.  Our bikes tend to run lean in stock, so I doubt changing the jets hurt it in any way...

I would probably check for leaks at this point, if carb fuel level checks out, and the spark plugs check out, since you have already done the things I would think of before the carbs like the tank filter and petcock.

My last thought was elevation - but I wouldn't think it would play this much into a problem.

- Bboy

BockinBboy,  Thank you for your tips. 

I'll have to look for the youtube video you are referencing.  I'm assuming it is something alluding to the float height?  This is something that I haven't checked whilst on the bike.  But i did (at least attempt) to do it while rebuilding the carbs.  I'll have to make sure to check that

You are right, with the cost of spark plugs, i'll have to order a set and try them out.  If nothing else it would eliminate one variable as you say.

My next plan of attack (upon confirming the float height), is to bypass the aftermarket fuel valve with a t-fitting.  That would rule out any possible issues above the carbs, as you would flow fuel from both the main and reserve feed.  Also, i'll have to look for leaks using started fluid.  At this point, i'd be happy to find anything just so I have something to point the finger at. 

Thanks again for your guidance
Brian

Here you go. I should have included a link earlier. Literally, 'U-tube Method' 

http://www.bbburma.net/FloatHeight.htm

- Bboy

This morning I had a few spare minutes so I checked the float height on my GS.  Both sides checked out nenar the head gasket (about 1mm over).  So it appears that this is not the culprit. 

This again leaves me perplexed.  When i get the chance i'll get a new set of spark plugs and try bypassing the after-market petcock.  Then i'll be really really stumped.

Thanks again to all those who have weighed in

Brian

Last night I got the chance to test ride the bike with the new, stock, spark plugs.  It still refused to run.  In fact, it may be getting worse.  Now it seems as though there is a lean surge at 50mph, not the 70 like it used to be.

I then bypassed the after-market petcock (a blind stab in the dark), and again nothing.  The behavior of the 50mph lean surge persisted.

At this point I am up a size on the mains, and up two sizes on the pilots.  I have not shimmed the jets, but considering the fact that the performance has gotten worse as I have gone up in jet sizes, I don't think that is the issue. 

Again, i'll take any and all suggestions that people can come up with.

Brian

When you replaced the stock petcock, what did you with the vacuum pipe from the carbs?

You should have blocked it off, if it isnt blocked off, it could be causing your lean condition.

Also, for the surging, check the chain tightness and condition. That can also cause a surge at certain speeds.

I agree with vinny.  It sounds like there is an air leak somewhere.  Make sure your airbox boots are tight around the outside of the carb mouth, and your carb boots are fully seated and tight on the intake.  Also make sure that your carb breather tube is kept out of the wind.  It should terminate behind the airbox and be held there by one of those flexible clamps that is screwed un under the bottom left corner of the air filter. 

Oh and for sure if you haven't already, you have to cap off the place where the vacuum line attaches to the left carb if you are going to run a non-vacuum petcock.  I used one of the same kind of caps that go on top of the carb sync ports.

For a stock setup, 125/40/3 turns should be perfect give or take half a turn on the mixture.  You can probably get away with 42.5 pilots, but I would think you would want fewer turns out to avoid being rich at idle.

Thank you both for weighing in.  I made sure to block the vacuum line coming out of the carb when installing the non-vacuum pet chicken.  I used a short piece of the original tube, blocked with a dowel/pin. 

Also, I went all around the carb/airbox area with starter fluid, spraying it in the direction of points where leaks could occur.  I noticed no idle change whilst doing this, which would seem to indicate no leaks of air.

As for chain tightness, I have adjusted the chain to factory settings.

I have been advised to check compression, which I will do this evening.  I also am going to take it for a ride and see how it performs with the gas cap open.  Although I don't think that is the issue, i'm really scratching the bottom of my barrel at this point.  Short of that, i'm looking for a set of running carbs that I can replace my carbs with just to see if that is really the culprit.

If there is anyone in the Detroit area that has a functioning GS500e that they wouldn't mind me swapping the carbs off of, just to see if it will run on my bike, that would be awesome.  I would be willing to come to wherever would be convenient.

Or, if someone is selling a set of functioning carbs, please PM me

Thank you guys again for the insight.  I appreciate it

Brian

I bet you have a 'bad' igniter, or sumptin else ignition related.

Pinched fuel lines?

Is the undertank petcock full open - the slot facing totally vertical?

No other fuel filters in the system?

Michael

Tonight I went through the carbs again.  Tomorrow i'll be soaking them in carb cleaner and then i'll reassemble them.  I came across one thing of interest.  There appears to be a crack in the tube for the enrichment circuit on both carbs.  Attached is a picture (assuming I figured out how to attach a picture).



In regards to the recent suggestions:  The fuel lines have been straightened, although that was something that I was fearful of initially.  The tank chicken is fully open, I figured that one out the hard way by spilling gas all over my drive way.  I have a fuel filter on both the main and reserve line.  While this definitely could limit the flow, when I connect both main and reserve lines to the carbs via the t-fitting I still have all the same behaviors.

In regards to a bad igniter (coil, plug wires, harness, etc), I would think if that were the case one plug would appear more brown than the other.  But, both carbs are equally white.  This leaves me perplexed.

Thank you guys for offering your suggestions.  I wish that they all were the solution to the problem so I could stop tearing the carbs apart and just start using the bike.

Brian

Quote from: gilkeyb on July 23, 2012, 08:34:36 PM
Tomorrow i'll be soaking them in carb cleaner and then i'll reassemble them.

That is generally frowned upon - too many plastic parts that are not generally supposed to be removed.

Only soak 100% metal parts. Which might be what you meant, but some people have really screwed a carb by forgetting plastic bits they don't see and then melting them in carb cleaner.

What the Haynes manual says: Caution - the carburetor bodies contain plastic parts that cannot be removed. Do not dip the carburetor bodies

You have been warned, hopefully in time.

Everything in this thread seems to point to a vacuum leak to me. Have you tried spraying starting fluid around the carburetor?

I would also try to ride the bike around at a lower speed which you haven't experienced problems with, only ride a gear or two lower than you normally would. The higher revs will give you a stronger intake vacuum making any leaks between the carb and engine more apparent.

Also, if you can safely/legally do it, try maintaining full throttle in gear 6 to see if you have the same symptoms (steep hill maybe?). If you can do that without surging it means fuel delivery is not your problem, and again points to a vacuum leak.

Upon going through the carbs last night I returned to an issue I noticed when first breaking them down.  The gaskets on the bottom end of the guides look pretty shoddy on both carbs, and they weren't included in the rebuild kits.  Does this picture look like something that could cause issues?  And if so, does anyone know where to get that part, be it just teh o-ring or the whole guide?

Quote from: Badot on July 23, 2012, 09:56:01 PM
Everything in this thread seems to point to a vacuum leak to me. Have you tried spraying starting fluid around the carburetor?

I would also try to ride the bike around at a lower speed which you haven't experienced problems with, only ride a gear or two lower than you normally would. The higher revs will give you a stronger intake vacuum making any leaks between the carb and engine more apparent.

Also, if you can safely/legally do it, try maintaining full throttle in gear 6 to see if you have the same symptoms (steep hill maybe?). If you can do that without surging it means fuel delivery is not your problem, and again points to a vacuum leak.

I couldn't agree with you more.  I have tried spraying starter fluid all around the carbs, on both the airbox and engine side.  I'll try this again once I put the carbs back together, but it didn't appear to be the issue before.

Before I rejetted the bike, it would pull in 6th at WOT throttle well.  But after rejetting it will no longer do this.  It pulls decently in 6th up to about 70, but not beyond.

Every time I touch the carbs on this bike, performance changes (sometimes for the better, sometimes for the worse).  So that seems to point to the fact that the issue is infact in the carbs.  Although, a deeper concern is that there is some type of leak in the engine, which would most likely be catastrophic.  I have to contact the auto parts store to see if they loan out compression checkers, as mine doesn't have the right threads.

Brian

You most likely won't find a compression tester with the right threads at the auto parts store.  At least I couldn't.  I ended up buying one.  I'm strongly leaning toward the issue being in the carbs and not the engine anyway. 

I don't think that the small crack in the enrichment circuit tube will affect much, but I'm not 100% on that.  Maybe it could be fixed with some solder?  The o-ring at the bottom of the white slide holder, I've never been able to source that one.  Yours doesn't look terrible, I've seen worse (albeit not in a running carb).  I would just rub some 2-cycle oil on it and make sure it has integrity.  It gets pressed down into the carb and tighted down with the main jet screwing into the emulsion tube anyway.

One thing for you to check would be the diaphragms.  You might have a hole in a diaphragm, or they could just be very stiff and preventing the slide from moving as it should.  One sign of this would be if you have to do a lot of work to get them back into the groove for reassembly.  I replaced my diaphragms that didn't even look that bad, and it helped the bike feel much more smooth and responsive.

I think the best test for you at this point would be a carb swap with something with working carbs.