Hi All,

I've been lurkin' awhile, and, after three days of rejetting woes, I'm ready to ask for help. I have a 94 GS500 with almost 10k miles. It runs (or did run) pretty well, despite the PO using it as a commuter and neglecting nearly all aesthetic aspects of the bike.

After reading about the benefits of rejetting, I decided I'd give it a try. The bike had the stock airbox and exhaust with stock jets (37.5/122.5). I went ahead and ordered 40 pilots and 125 mains and bought myself some #4 washers. After trying nearly every combination of washer from 1 to 3 and every possible air mix screw setting, I could not get the bike to run right.

It started and idled perfectly, the midrange power was there, and it sounded throaty as hell compared to stock, BUT, it fell flat at around 7k rpms. It didn't bog, it didn't backfire, etc. it just kinda lost pull. The engine revved and made a bunch of noise, but just stopped pulling. At first I thought I had the needles in wrong so I double-checked all that stuff and everything was correct as far as I could tell.

From what I've read, the main jet determines fuel supply at higher RPMs so I'm wondering if I just need to go up to a 127.5 main (and the fact that the Dynojet Stage 1 comes with a 128 makes me fairly confident that that's my issue). As for elevation, I live in New York City.

My hats off to the user and moderators whose enthusiasm and knowledge make this site such a great resource. Any and all advice is appreciated!

Thanks!
RC

I did the same thing and had the same issue. Solved with K&N luchbox air filter. BTW 1 washer was fine for me.

Interesting - thanks for the reply. So it was too rich, I guess? And the lunchbox leaned it out?

Keep in mind, the benefits are mostly when it's not stock anymore. Yes it may run a little lean as it sits stock, but only just. It is worth changing out the air filter and rejetting for that, but only if you were going to do it anyway.

DJ 128 is not real 128 - cos their needle is a lot thinner ...
Its easier to fix it with the 40/125 you have.

OK lets start with the basics.

Carbs: Assuming all fuel passages are clean - problems @ 7K - what throttle position ? is the emulsion tube holes clean and the O ring @ the bottom of it in good shape ? How about float level and O rings in that.

Then air flow: Air box - all hoses intact in that ?
Air filter - clean ?
Exhaust ? pipe or stock ? is it loose @ the head or nice and tight.

Then float level ? where is it on the U tube check.

Just back to Basics, you're pretty close.

Falls flat @ 7K - but @ what throttle setting ? and is it when you open the throttle or @ steady throttle ?

And is it better if you open throttle slowly than when you whack it open ?

Its easier with 40/125, do not ever buy a DJ kit. Ever ...

Cool.
Buddha.

Quote from: younastytwin on July 09, 2013, 07:02:16 AM

The engine revved and made a bunch of noise, but just stopped pulling.

This sounds like a slipping clutch - did it rev but not increase the speed lock step ?

Cool.
Buddha.

Ok, so first, I'm gonna rule out the slipping clutch because I know what that feels and it would be an insane coincidence if it just now started slipping. And it's not like free revving at that point or anything.

I'm gonna say that all fuel passages were clean. The emulsion tubes seem clean but I did not check the o-rings at the bottom. I did actually just notice some gas on the left side of the air box so that could be an issue. I saw a post on here about that but couldn't figure out which size to buy at the auto parts store (nitrile not rubber, check). Any ideas on that?

Still, it ran well in the higher range before I did anything so I guess if the o-ring down there is bad it's just a coincidence that it went at the same time I rejetted?

As for airflow, all hoses are intact (checked on two different diagrams), it has a new stock air filter, and I've just repainted the exhaust and know it's tight (because it was loose when I started it up the first time to cure the pipes and definitely know what that results in).

As far as throttle setting when it falls flat, it didn't really seem to matter whether I was wide open, steady, or whacking it.

Sorry, I didn't respond to float height. I didn't actually check that - just left it as it was (tangs looked the same and neither seemed like it had ever been adjusted).

Floats drift higher, looking like its never been adjusted means nothing, they dont look bent after you adjust them. Its likely to be high.
Fuel on left side of airbox ? gravity, and side stand ? Float is overflowing likely.

And the throttle position @ which you're having issues - 7K is fine, but is it @ 1/2 throttle, 3/4 throttle ?

And it acts up @ that position in all circumstances - steady, opening slow, or opening fast ?

I think your floats should be set right, and try it again. 1 change at a time and find out what it did.

Cool.
Buddha.

My EX-500 project has a similar problem. Above 70mph it just won't go much faster.
I know the clutch needs adjustment. The catch point is very small with not much slipping range before engaging. My bet is the clutch is engaging but not fully. When going for high speeds and RPM's, it starts slipping.
Right at the point the clutch lever gets free play, the clutch engages. That means the clutch needs adjustment at the engine end.

So try a proper clutch adjustment before tearing into the carbs and other stuff. It is fast and easy on a GS500. Plus, it won't hurt and may save you from doing lots of unnecessary work.

Next weekend I'll be adjusting the EX-500 clutch. 2 of us rode it last weekend and came to the same conclusion.

All good questions. I'm going to check the o-rings on the carb needle seats and then adjust the float heights. After that, I'll give you a solid answer on throttle positions, etc. because I'm not 100% sure.

Thanks again, I appreciate. I'll be back in touch.

Adidasguy - thanks for your reply. Totally worth checking out, but it was fine right until I did the rejet. Would be an amazing coincidence if the clutch faltered exactly when I put the new jets in, ya know?

I missed part of it.
1. Perfectly good running bike.
2. Did rejet for some reason
3. Bike doesn't run so good anymore
Conclusion: messed up the rejet.

Possible floats are low. Possible you have dirty frame petcock or pinched fuel lines since your fuel demands are higher than before.

"If it ain't broke, don't fix it."

Quote from: younastytwin on July 09, 2013, 10:22:05 AM
Adidasguy - thanks for your reply. Totally worth checking out, but it was fine right until I did the rejet. Would be an amazing coincidence if the clutch faltered exactly when I put the new jets in, ya know?

When jetted right. the thing make a wee bit more power. It also runs a wee bit cooler. Cooler = cooler oil = slipperier ... more power+ slipperier oil = slip.
Anyway maybe clutch, maybe not.
Cool.
Buddha

Ok, so I checked the o-rings and they looked fine so I cleaned them and put them back in. I tried to measure the float height and it seemed a few mm over the standard 14.6, assuming I measured correctly. That's a very tough measurement to get precisely, btw.

Ok Buddha:

Still, it worked fine before with those float heights and I didn't want to exacerbate the problem by futzing with yet another variable. Since I'm riding this weekend, I decided to see if I could get it running right with the old main jets (122.5).

I installed the old jets and turned the air/fuel screw TURNS turns out. It ran totally flat so I brought the screws out a half turn at a time - many flat spots along the way - until I arrived at a whopping SIX turns out. Then it ran great - like it used to. So now I feel like I just never turned the screws far enough out when I had the 125s in? Does that make any sense? I am at sea level (NYC) so maybe I just needed it a lot richer to compensate for air density here?

Or is that compensating for a bad float height in some way?

Also, I nearly stripped one of the screws and I'm having a hard time finding a new one - or better yet, one of those fancy easy adjust ones. Anybody have ideas on where I can get either?

You set them 6 turns out from small screwdriver bit "lightly" seated or from long screwdriver gorilla seated? It makes a diference.
As for the flat spots, I think you might be masking other (needle jet, main jet, vaccum) problems with that much "turns out" on the mixture scew, someone correct me if I'm wrong...

Also, when you disassembled the carbs, didn't you forgot those tiny orings on the vaccum chamber caps? Are both the vaccuum ports plugged?

And...when you whan to see if it's running too lean or too rich, stick a bit of duct tape at the air filter openning, covering like 1/3 of the openning. If the flat spot disappears it was because it was lean, if it's worse you were already running rich.

With 122.5 you have 6 turns ?
You have 40 pilots in ?
Some else is wrong - 6 - 1/2 turns or 6 full turns ... and yes lightly seated like GSXR 750 guy said ? - finger tip on small screwdriver, or ham fisted 2 hands and a bench vice ?
Your float height is @ the top of the bowl ? I dont know this mm BS.

Cool.
Buddha.

Yep, I've got the 40 pilots in and the 122.5 mains now. O-ring and cap on vacuum ports are good. And as far as turns, I lightly torqued them down before screwing out - not gorilla style, but like it needed to be firmly seated but I didn't want to strip out anything/go too far.

On the float height, I measured by turning carb on it's side with the needles at the top. Then I leaned it over to the left until the float started to touch/pull out the needle by the little hook/bale thing on top. When I did this, the distance from the float and the edge of the bowl where the gasket would go was well over 14.6mm. Does that mean my float is low and it's not getting enough gas in the bowl?

It's such an imprecise and difficult measurement that I'd almost just buy new floats if they were set up properly when shipped. Is that usually the case, or would I have to adjust those too?

Thanks again, guys.

To top it off, I've just discoved the bike was in the PRIME position (not ON). With the larger end of the know at the bottome and the arrow pointing up. Do I need to change my oil now?

The only way to be sure about the float height is to check them with a clear tube while installed on the bike. Do that. It's already been suggested twice, maybe the third time is the charm.