it was a perfectly good motorcycle...

[adidasguy]

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.

[piresito]

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...

[younastytwin]

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.

[piresito]

Like your signature BTW.... 

[bombsquad83]

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.

[younastytwin]

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?

[piresito]

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

[The Buddha]

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.

[younastytwin]

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!

[younastytwin]

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]

[bombsquad83]

I think replacing diaphragms is a great idea.  I did the same and it made the bike perform much more consistently.

[The Buddha]

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.

[The Buddha]

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.

[BockinBboy]

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?   

Sincerely. 

- Bboy

[weedahoe]

IDK if its been said and I didnt read through everything but make sure you also synch the carbs

[younastytwin]

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!

[The Buddha]

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.

[younastytwin]

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.

[bombsquad83]

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. 

[DrtRydr23]

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.