93 GSXR1000 carbs

[audijunky]

they didn't quite fit, but after some modifications got them on. Now the tuning begins, and that is where I would like some help.
So got it running , sounds good with full choke, can rev it up with full choke but kinda hangs at the top for a few seconds after releasing the throttle. barely idles without choke, cant rev without choke either, when applying throttle w/out choke it dies. at this time I dont have any air filters on them, and have straight pipes 4-2 headers. Anyways got me thinking lean condition. SO pull the carbs and check mains. they are 124, got to looking at my assembly of carb parts and have the original 137's out of the XS carbs. the threads match and the same diameter so I put them in. Only thing is the GSXR mains are a little longer, so I was not able to put the washers in under the XS mains. Haven't tried it yet, was wondering if I should check anything else while I have them off. Any idea if the pilot screws form the XS carbs wil fit the GSXR carbs too? if so would going up one size, or to the smallest I have be beneficial? And I dont know how these mixture screws work, fuel or air? any idea how many turns out I should start at?

thanks a bunch in advance GURU's or anyone else who has some suggestions

[Shuriken]

So got it running , sounds good with full choke, can rev it up with full choke but kinda hangs at the top for a few seconds after releasing the throttle. barely idles without choke, cant rev without choke either, when applying throttle w/out choke it dies. at this time I dont have any air filters on them, and have straight pipes 4-2 headers. Anyways got me thinking lean condition.

No air filters = lean
Straight pipes = lean

You have 2 known lean conditions there. You suspect even jetting might be too lean (running better with choke on).

Here's what I would do - just my opinions of course... I would put the bike in the condition you plan to operate it in before you start tuning. By that I mean getting the exhaust system on that you will be using on the bike or to pass inspection with. If you plan to run no mufflers all the time, disregard this. I would also choose the air filters you are going to use and get them on there. For example, pods. With some air filters and mufflers, then I would repeat your running test prior to messing with jets and see what happens. Does it run better without the choke on? I'll bet it will. Then check your spark plug color on the idle range, mid range, and full range, because it sounds like you haven't done that yet. White plugs? Probably not black.

When I put ZRX carbs on my 79sf, I immediately looked at plug color and all 4 plugs were black. This was with a 4-1 exhaust and everything else stock, at 5700ft elevation. So I started messing with things, trying to go leaner, especially the jet needle position. Then I tested and the bike ran worse. It dawned on me that I was using soot-fouled plugs from before. The bike was now warmed up but showing black plugs, so with it already being warm, I swapped in some fresh plugs, took it for a spin, checked plug color, brought it back. To my shock, the plugs were now white! I went from soot black to white by just adjusting the jet needle position. This didn't make total sense to me but what did make sense was that I was trying to check plug color on pre-fouled plugs. One can't rely on the engine to "clean the plugs."

So I set the ZRX carbs back to the stock jet needle position and tested again and I got a beautiful color on all 4 plugs. I didn't do anything at all to change jetting. In 6 years of dealing with "carb hell" as they say around here, I had never been able to get such a nice, consistent, even plug color at my elevation with the stock carbs. I got it right away with the ZRX carbs.

The ZRX carbs fit almost perfectly. Everything improved as far as carburetion. The only thing I had to deal with after the swap was starting the bike. I had to use full choke to start it almost all the time.

[Shuriken]

I forgot to mention that I would also make sure I didn't have any air leaks through the intake boots that your carbs are fitting into (a possible 3rd lean condition). Carefully spray an aerosol around them to see if idle speed increases.... what do people use for this, WD-40?

Also - again just my opinion - a possible 4th lean condition would maybe be your elevation - at least compared to mine. I have to jet all of my bikes leaner where I live. So IF these possible conditions are added to the existing 2, and if all 4 conditions are at play here, that may explain the running condition that you described.

BTW - do you have any pics of your modded bike that you could post? Sounds like a very interesting project...

[oldyam80sg]

I have a 99 ZRX and was wondering how is the bike power wise with the carbs in place on your XS?I know the ZRX scares me sometimes if i give it alot of throttle because it will immediately take off,just curious.

[audijunky]

I got a few pics, this one is the best though (has a rear fender now)



I have a 05 ZRX1200 too


what year ZRX are your carbs off of? I measured the spacing on mine compared to the XS and they didn't match up. cant remember now what they were though. Anyway
plugs were white, didn't do plug drop though, just checked them after idling and reving some, couldn't do a plug drop actually. I am at like 80 feet above sea level, so I am pretty sure I need bigger jets, probably need to raise needles. Haven't sprayed anything around boots yet with these on, but did do it with the originals on. Also was searching and read your post on the GSXR carbs good info, thanks for posting. to answer some questions, going to be running pods, dont have em right now, pipes are staying as is for now.

When doing the plug color testing, am I incorrect in assuming the motor has to be under load? right now I dont want to ride it until I can atleast get it to idle and rev without the choke on.
When I get home I am gonna check float height, adjust mixture screws, see where the needles are set, and see what happens from there with the
137 mains I put in. This monster has very little air restriction, so I am thinking the stock fuel jets are to small.
thanks for posting
How is it running with those ZRX carbs? Gotten it Dynoed?

[Shuriken]

I have a 99 ZRX and was wondering how is the bike power wise with the carbs in place on your XS?I know the ZRX scares me sometimes if i give it alot of throttle because it will immediately take off,just curious.

It had good power but nothing scary. Your ZRX would stomp all over it.

The bike had crap exhaust when I got it and I put a 4-1 on it, so I lost some bottom end but the bike would really wake up nice for a 79 when you took it bast 5500. My reasoning in trying the ZRX carbs wasn't really for power but for management. They were 2003 carbs and were pristine. Easy to get parts for and relatively cheap. Easy to work on. They were clean, also. But the best part is that they gave me a good fuel/air mix! No more black sooty plugs.

This review makes me really want to own a ZRX:
http://www.motorcycledaily.com/26mar...1zxr1200r.html

I used to like where Suzuki and Yamaha were going with the Bandit and FZ1, but manufacturers keep raising the powerband and making the bikes more aggressive. The ZRX, Bandit, and FZ1 used to be the swiss army knife of bikes, but they are more and more a sport bike. I'd still snatch up a ZRX though!

[Shuriken]

what year ZRX are your carbs off of? I measured the spacing on mine compared to the XS and they didn't match up. cant remember now what they were though.

Yeah, they aren't a perfect match. I had to be creative to fit them, but they did fit into the stock manifolds without any mods. IIRC, the #2 and #3 were a bit too close together? I think mine were from an 03, non-California jetting.

Anyway
plugs were white, didn't do plug drop though, just checked them after idling and reving some, couldn't do a plug drop actually. I am at like 80 feet above sea level, so I am pretty sure I need bigger jets, probably need to raise needles. Haven't sprayed anything around boots yet with these on, but did do it with the originals on. Also was searching and read your post on the GSXR carbs good info, thanks for posting. to answer some questions, going to be running pods, dont have em right now, pipes are staying as is for now.

Gotta be too lean. 80ft ASL is way different than 5700ft ASL! Dan Hodges on here said a good rule of thumb is to go 1 size leaner for each 2,000ft above sea level. I wonder how you could calculate jetting in your case where you need to go richer? Someone on here had a formula to help with jetting that took into account the changes and what each change would approximately mean in terms of jets... so if you had no mufflers, that was a +1 and if you had pods, that was a +2 and so forth.. you added it up and it helped you get in the jetting ballpark.... it'll turn up somewhere....

But if you are going to mess with jetting, I do think you should start with the main jet first. What happened when you put your XS Mikuni 137's in the GSXR carbs? That is quite a size increase but is the way that each manufacturer measures a uniform measurement? Is a Mikuni flat round 137 the same as a Keihin 137? I would think you would definitely see a change with 4 137's in there...

When doing the plug color testing, am I incorrect in assuming the motor has to be under load? right now I dont want to ride it until I can atleast get it to idle and rev without the choke on.
When I get home I am gonna check float height, adjust mixture screws, see where the needles are set, and see what happens from there with the
137 mains I put in. This monster has very little air restriction, so I am thinking the stock fuel jets are to small.
thanks for posting
How is it running with those ZRX carbs? Gotten it Dynoed?

I think you are correct that you want the engine to be under load when you are going to do a plug test. A slight uphill is recommended. I would look up specs for those carbs and check float height to spec. I wouldn't mess with more than one carb variable at once. I would spec the float height and then just mess with idle mix screws. If you have a ColorTune (glass spark plug) like I had, you can just turn the screws out until you see the flame turn blue. But if your pilot jets are too small, you'll be able to turn the screws completely out and never get a blue flame... In fact, you should get a ColorTune and see what color the flame is when you can get the bike to idle with choke on. IMO, a ColorTune is vital when you are going to put different carbs on the XS.

Unfortunately, I never got the bike dynoed. I did find an obscure Harley Davidson shop 45mins away that said they would dyno any of my street bikes, but they do look at and talk to me funny when I mention that the bikes are 4 cylinder! Plus, it's more expensive than a dyno shop in a big city that does a lot of tests....

[petejw]

Hey Audi,
I had the same problem as you with the zrx carbs, the mains
fitted were 95 i had to go to 130 mains to have the engine run.
Your right in thinking to check the carbs, to have the bike under load,
a nice long hill works well. If the bike is coughing and splattering under load, its usually rich, if its flat or pinging its lean. If it runs better when cold its rich if it runs better when its hot, its lean.

[audijunky]

Allrighty then, got it idling without choke. SO far I have installed the XS 137 mains, (luckily these old GSXR carbs are Mikunis), and installed 42.5 pilots. Also adjustd the float heights to 14mm. Somebody on here in one of the older forums said that was the stock float height for the GSXR carbs. I also checked the needles and they were set at the second fromt he bottom position, so I moved them up one clip position to 4 down. I did notice on these that for some reason carbs 2-3 had a shorter spring above the diaphram, whats up with that, anyone else run itno this. I hope its normal and not some silly mod the PO of these carbs tried. What I did forget to do in my haste was check/adjust the idle mix screws. Whickh I am sure is a big deal. Anyway idling good, get some hesitation when reving it up, and when riding it. God I love tuning carbs with the butt dyno!!! Gonna have to pull these bastards off again and check/adjust mix screws, I think I am gonna start with 2 1/4 turns out, what do yal think?

[DiverRay]

Why do you pull the carbs to adjust the mixture screw????? You need to do that ON THE BIKE, WITH A FAN BLOWING OVER THE ENGINE!. Read the tech tips on carbs and Kens write up on how to adjust it. You WILL need to adjust the sync at the same time, as everything is connected. It takes me about an hour to two hours getting everything set up once the jetting is close.

[audijunky]

I know you dont have to, I havent looked at these at all, I have know Idea where they are set, so I want to pull them to get them all the same to start with and double check my bench sync. Last time I tried that on my XS carbs I got the tip stuck from turning it in too far, and that was a PITA. So I figure I will pull them first to make sure I don't do it again

[CatatonicBug]

It takes me about an hour to two hours getting everything set up once the jetting is close.

Why does it take you so long? I just did mine, and it took about 20 minutes total to sync, adjust the mixture screws with colortune, then synch again.

[audijunky]

Some people do things different and maybe are more methodical and exact. sh-t 2 hours isn't long I have been trying to get the ol XS carbs right for 2 YEARS!! And have given up, thats why I started this thread

[Shuriken]

Allrighty then, got it idling without choke. SO far I have installed the XS 137 mains, (luckily these old GSXR carbs are Mikunis), and installed 42.5 pilots. Also adjustd the float heights to 14mm. Somebody on here in one of the older forums said that was the stock float height for the GSXR carbs. I also checked the needles and they were set at the second fromt he bottom position, so I moved them up one clip position to 4 down. I did notice on these that for some reason carbs 2-3 had a shorter spring above the diaphram, whats up with that, anyone else run itno this. I hope its normal and not some silly mod the PO of these carbs tried. What I did forget to do in my haste was check/adjust the idle mix screws. Whickh I am sure is a big deal. Anyway idling good, get some hesitation when reving it up, and when riding it. God I love tuning carbs with the butt dyno!!! Gonna have to pull these bastards off again and check/adjust mix screws, I think I am gonna start with 2 1/4 turns out, what do yal think?

That's interesting about the shorter spring lengths. I would probably be inclined to match all 4. But who knows. Typically, the inner 2 cyls on these engines will receive less air cooling, so they should run hotter and also a bit more rich. If shorter springs allow for faster jet needle response, that would be weird because when the jet needle comes out of the needle jet, it allows *more* fuel to flow out. If you are already rich on cyls 2 and 3, why would you put shorter springs on just those two cyls to increase an already rich condition?

Pay close attention to what throttle opening causes the hesitations. You have 3 carb circuits and each overlaps a bit - idle, mid, and full. If you can say that for example, it hesitates at 1/8 throttle for example, I would look hard at the idle mix and float height. If you get a hesitation at mid throttle, mess with your jet needle. If it doesn't run well on full throttle, I'd start back at scratch with a larger main jet and work back down again. I always start from the top down - main jet, jet needle, pilot jet. Plug color testing is vital if you want to see where you're at. That or an A/F dyno test.

[audijunky]

Yep yep, thats the next step, just gotta find the time now, only get about an hour or two each night (weekdays) if that