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.
When the bike is running, PRIME is the same as RESERVE.
PRIME only bypasses the need for vacuum to let fuel flow. Used when carbs are empty or you ran out of gas and need to get the carbs filled again.
When the bike is running or not, the floats in the carbs control the fuel flow. If floats are not right and always let fuel in, you'd still flood out when running (just not as fast as some gas is being used). When stopped, if floats are stuck then extra fuel will flood the carbs in PRIME. With that in mind, PRIME or not, if there is flooding then it is the carb floats that need attention.
Quote from: younastytwin on July 10, 2013, 01:30:20 PM
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?
Did you lost a significant portion of gas? Didi your oil lever raised? If so, or in doubt, change the oil.
Now, for the carbs. Keep in mind that these are very simple carbs, and there isn't much that can go wrong (try compare it to a SRAD 750 carbs).
So, use the clear tube method to check the float height. It's the only way to know for sure, even knowing that everytime I've measured with a ruller and carbs upside down, then compare it later with the clear tube method, they match up really well.
1- Does that check's up? If it does, don't mess with it anymore.
2 - When you rev the bike, sitting without airbox, do the slides go up and down evenly?
3 - Spray WD40, starter fluid, etc, around the carb boots and vaccum chambers. Does the idle changes?
If 1 & 2,are yes, and 3 is no, then you probably have a adjustment problem.
Start with known good configuration, 125 main (are those real mikuni or aftermarket??), 40 pilot, 1 washer in the needles, and 3 turns out from lightly seated (dont forget that that screw, tightents against an oring, after lightly seated you're squeezing that oring).
The, if you feel flat spots, duct tape in the air filter. Then you know it it's lean or rich. Other way, you will be guessing.
Also, keep in mind that the pilot jet provides fuel for the idle up to around 1/8? opening of thottle. Then needles start to kick in...then, at full WOT kamikaze run you're running in the main jet openning. Floats also make a diference, but if their lever is ok, there are no need to change anything in them.
You can't rely much on Rpms, when checking for flat spots/even pull I use to open the throttle slowly as rpms go up, like if the throttle hand was connected to the tachometer. You also need to check how it pull's from 3K rpm with a WOT, but that's another check.
Also, it crossed my mind that you're now using more gas, maybe you plugs are too bad to burn it all? A long shot, the least probable, but it might worth checking...
Yep, fair enough. I found the video and I'm shopping for a clear hose today. Will change my oil, check float level, adjust if necessary and then post my findings.
Thanks a million for everyone's help on this. As they say on Spartacus: gratitude.
Like your signature BTW.... :icon_mrgreen:
Quote from: piresito on July 11, 2013, 02:37:36 AM
Start with known good configuration, 125 main (are those real mikuni or aftermarket??), 40 pilot, 1 washer in the needles, and 3 turns out from lightly seated (dont forget that that screw, tightents against an oring, after lightly seated you're squeezing that oring).
This would be key. Make sure that the jets you are trying to use are genuine mikuni jets, otherwise the sizing could be off. Also, make sure the pilots are the "non-bleed" kind. They should not have holes in the side of the jet, just in the top and bottom. Beyond that, I think checking the float height with the clear tube method, and checking for air leaks by spraying WD-40 around the carb boots are great areas to check for issues.
You guys are killing it - thanks again.
Just a little update here:
Jets are genuine Mikuni (pilots don't have holes in the side), float height was exactly at 14mm (and confirmed with float height check trick), and the plugs are new (400 miles, max).
When re-installing the carbs, I discovered (and then made worse) a tear in one of the air intake tubes. After getting it back together, I shot some WD-40 on it and the idle spiked. SO, this is likely the culprit, right?
I've ordered the intake tubes along with new fuel and vacuum lines. To be continued.
In the meantime, I stripped one of my fuel/air screws - any of you guys still selling these?
Quote from: younastytwin on July 13, 2013, 08:28:03 PM
When re-installing the carbs, I discovered (and then made worse) a tear in one of the air intake tubes. After getting it back together, I shot some WD-40 on it and the idle spiked. SO, this is likely the culprit, right?
I've ordered the intake tubes along with new fuel and vacuum lines. To be continued.
In the meantime, I stripped one of my fuel/air screws - any of you guys still selling these?
That's likely the culprit, at least, the bike will never run well with that crack.
As for those screws, try to contact Adidasguy, he has every part for the GS in duplicate! lol
Intake manifold leak - yes you have to fix that before getting on with more tuning.
But, if you have K&N pods, the new manifolds you get these days dont fit as well, the pods and carbs should be "held in" a bit better by other means, like a block of wood in front of the battery box - you gotta give the K&N+carb set - "nowhere to go".
Cool.
Buddha.
Yeah, I wondered about that. I'm sticking with the stock box for now while I clean up the bike and hopefully put a few miles on it. But I definitely think some kind of mounting brace would be in order in the absence of the airbox and screws that anchor it to the frame...
I'll be back with an update as soon as the parts get here... thanks!
Hey fellas, thanks again for your contributions. Just thought I'd give a quick update.
I installed the new intake pipes/manifolds with new o-rings and that seemed to even everything out a bit and bring it back to life but not quite where i wanted to be. In the meantime, I said eff it and bought a drop-in K&N and 127.5 mains.
So I ran the K&N with the 125 mains and it was still flat. Sounded better, maybe even a little more mid-range power but ultimately still flat. I then cleaned the carbs and added the 127.5 mains, and put in all new o-rings, gaskets, needles, etc. and confirmed my float height to be correct by every measure I could find.
I put it back together, fired it up and took a drive. Good low-end, dead flat spot around 4500/5000, climbed to 6000 and then BANG. LIGHTNING. Bike just tore off, revving and pulling hard to almost 9k. Completely different bike. Just incredible.
I read that jetting FAQ from the Factorypro site that somebody had posted here so I decided I'd move on to the mid-range and added a 2nd washer, so now I have 2. Well that flattened the whole thing out again, which was strange. I decide to go back to just the one washer. Now it runs totally flat - but at least even. No more dead spot, but no more madman power from 6-9k. I can only assume the diaphragms - which don't really stretch all the way across the seat - are the problem. I think they've kind of withered/wasted and shrunken a bit. I must've got a good seal on them the one time it ran like a beast and then not done quite as good a job after the washer swaps.
So I ordered new diaphragms. Does my story check out? And do you think I'll ultimately need one or two washers with my 127.5 main/K&N drop-in/stock exhaust setup?
Thanks again, guys, I really appreciate the feedback.
RC
Oh, and just to "humanize" my bike, here's a pic:
[attachment deleted by admin]
I think replacing diaphragms is a great idea. I did the same and it made the bike perform much more consistently.
Stop stop stop ... random sheite ... stop, your diaphragms are fine if all they do is not stretch across all the way ... spray em with a shot of wd40 .. .wait 2 min, and wiggle em ...
Or send me the carbs and I'll seat your diaphrams free ...
Diaphragms are fine if you're getting to 9k ...
Let me read over the new post slowly ... I'll post back.
Cool.
Buddha.
Quote from: younastytwin on July 28, 2013, 06:53:51 PM
I then cleaned the carbs and added the 127.5 mains, and put in all new o-rings, gaskets, needles, etc. and confirmed my float height to be correct by every measure I could find.
I put it back together, fired it up and took a drive. Good low-end, dead flat spot around 4500/5000, climbed to 6000 and then BANG. LIGHTNING. Bike just tore off, revving and pulling hard to almost 9k. Completely different bike. Just incredible.
Oh no its purple ... so what you do is sell it and buy somehtign more ... lets say, not purply ...
OK anyway ... 4500-5000 flat spot may have been a case of the slides comming up too fast. Post that symptoms ... if you're able to get back to that stage ... I'm thinking you're rich or have slides comming up too quick.
Diaphragms are fine, you may need to go back to that setup. Then we will sort ourselfes from that.
Cool.
Buddha.
Fix it until its broke does seem to be the theme of this thread... started by a rejetting attempt you didn't get to run right in the first place, I would have turned back then... and now you've added things to the mix multiple times(literally to the mixture) and you are chasing a moving target. Kind of painful to watch, really. It does sound like you have the know-how to get it done, though my suggestion is one step at a time.
I'm not totally sure what you are wanting from this bike with the path you have taken/planned... but you have to remember it is a GS500 with 46hp... Do you want to ride it, or fiddle your wits away? I really do hope you get it running where you are satisfied, I'm just unsure whether this bike will do that for you? :dunno_black:
Sincerely. :cheers:
- Bboy
IDK if its been said and I didnt read through everything but make sure you also synch the carbs
Buddha:
You're not the first to razz me for the purple! Haha... I'm thinking white wheels, satin black frame and a 90s Grand Sport (GS!) Corvette blue paint job with white decals and a red "E" but let's get the thing running right first!
And sorry for the confusion - I actually did go back to the same setup where it ran well up to 9k (back to just the one washer, the K&N drop in and the 127.5 mains) but it was flat again. So I assumed that I had somehow seated the diaphragms better the first time (when the carbs were off the bike) than I did the second time when I added - and then removed - a second washer.
I appreciate the offer but will try to properly seat the old diaphragms in the meantime. Figure the rubber is almost 20 years old and I could stand the $35 for new diaphragms though, right? Or is that money spew?
Weedahoe:
I have a sync and it's on the list!
BockinBboy:
Totally get what you're saying and I'm acutely aware of how unscientific this is! :) Not sure if I have the know-how but I'm certainly acquiring it, one patience-testing Saturday at a time. I know it's not a 600, etc. and besides, I was really astonished/pleased at how well it ran the one time I almost got it right so I'm good with a GS for awhile I think.
I'm sticking with the K&N and whatever jet/washer combo will work from here - no more other random variable changes until I get this part sorted!
Older diaphragms are better than new. Seat em right, and made sure needle and the spring and whatever else also sits in there good.
You may have an issue with seating the thing, but that's not going to be rememdied by byuing a new set, those are the same size/type/fit as the ones in there.
If you see a rip in one, yes, replace it. Else they run forever ... I've lost 1 set in under 4-5k, and got 50+K out of others. Not really a wear item ... more like a gorilla item ... if its been mangled by a gorilla ... yea replace.
Cool.
Buddha.
Ok, Buddha, I feel ya on using the old stuff if it works but I had already ordered the new diaphragms and decided to give them a go. Bike runs like a maniac with the new ones, BUT, there is a small stumble around 4k when throttle is opened (past a quarter I'd say).
To recap, I'm running 40/127.5, just 1 washer, a K&N Drop In - without the little restrictor thing it came with, and stock exhaust. My floats are correct and my screws are set out to 3 turns out from a soft seat (right when I feel the o-ring engaging).
To get rid of the stumble, am I looking to add a washer - making it 2 - or am I just dealing with air mixture screws now?
Psyched for the replies.
Try putting the restrictor on and see how it goes. I could never get mine tuned quite right with the K&N drop-in. I didn't have the restrictor, and eventually I got tired of trying and went back to the stock filter and everything was all good again. You aren't gaining anything but frustrations by leaving the restrictor off IMHO. Only think I think might be worth trying would be going back to 125 mains (with the restrictor), if you can't get your current jetting to work. Remember to get the bike nice and warm before you judge too much about what you should do with the jetting.
Quote from: younastytwin on August 02, 2013, 12:36:23 PM
Ok, Buddha, I feel ya on using the old stuff if it works but I had already ordered the new diaphragms and decided to give them a go. Bike runs like a maniac with the new ones, BUT, there is a small stumble around 4k when throttle is opened (past a quarter I'd say).
To recap, I'm running 40/127.5, just 1 washer, a K&N Drop In - without the little restrictor thing it came with, and stock exhaust. My floats are correct and my screws are set out to 3 turns out from a soft seat (right when I feel the o-ring engaging).
To get rid of the stumble, am I looking to add a washer - making it 2 - or am I just dealing with air mixture screws now?
Psyched for the replies.
Try the carb sync now that its running better.