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I was just wondering about My 88 gixxer 750. I just put a newer engine in out of a 91 and installed the newer carburetors on it, and it seems to stutter just a bit when you first give it the gas, a little less than the original engine, but as soon as it puts a bit it has plenty power. I was just wondering if this is normal, or if maybe I need to get it rejetted or something. I really appreciate all the advice you guys can give. Thanks in advance!!!
 

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Mine runs like snot when it's cold, but once warmed up, there's no hesitation or "stutter" anywhere in the powerband... whack the throttle open and hang on. Did you use the ECU from the new engine as well, or keep your ECU from your old engine? That's something that can make a big difference. I'm sure the resident gurus can tell us what year ECU's are interchangeable...
 

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NaNaNaNO!
My 90 as no stutter at all. Just pulls hard (39 Keihen FCR's Dyna 2000) and my 88 7-11 Has no trouble at all (38 Mikuni RS's, Dyna 2000). If you are using the box from your 88 this is the problem. That box is programed diffently and also has a higher rev limiter than your new 91 engine can handle. The 88-89 box is different than the 85-87 or 90-92.
Bones

[ 05-21-2002, 01:52 AM: Message edited by: Bones_GSXR ]
 

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Discussion Starter #4
Thanks, everyone. Would you advise me to get an aftermarket box, like the vance and hines or something like that, or should I go stock and grab a newer one for the 91. Thanks again. This really helps.
 

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Mine has the same problem! Once I am above 4-5K rpm it is fine, but below that it isnt so good. I usually ride the clutch to get the RPM's above this point then it is fine. The hotter it gets the worse it is. I just replaced the CDI Box this season & re-did the carbs, but it did not help.

Cheers,
CarKnee
 

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My advice pacman is to take your bike to a race prep shop and get them to set up the carbs on a dyno. There is no better way to set up carbs.
I take it for granted that you have already stripped the carbs and cleaned them, checked that your valve gaps are OK and had the carbs balanced and put a clean air filter in ??.
I had my bike set up on a race shop dyno and it was the best 100 pounds(UK) I have spent on the bike, honest.

[ 05-21-2002, 12:59 PM: Message edited by: TorF3 ]
 

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Originally posted by TorF3:
My advice pacman is to take your bike to a race prep shop and get them to set up the carbs on a dyno. There is no better way to set up carbs.
I take it for granted that you have already stripped the carbs and cleaned them, checked that your valve gaps are OK and had the carbs balanced and put a clean air filter in ??.
I had my bike set up on a race shop dyno and it was the best 100 pounds(UK) I have spent on the bike, honest.
<font size="2" face="Verdana, Arial">Good advice; I had mine set up on a dyno as well and it's near-perfect... but no amount of carb-tuning will make up for the wrong ignition box.
 

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Originally posted by XLTRider:
Mine has the same problem! Once I am above 4-5K rpm it is fine, but below that it isnt so good. I usually ride the clutch to get the RPM's above this point then it is fine. The hotter it gets the worse it is. I just replaced the CDI Box this season & re-did the carbs, but it did not help.

Cheers,
CarKnee
<font size="2" face="Verdana, Arial">I'm embarrased to say I've got something similar, but it only happens at really low RPMs like under 2k. I had a really bad lean spot down low until I upped the pilot jet and now it runs great except sometime when you let out the clutch without giving it any gas it bogs. It doesn't seem to do it every time and it happens so infrequently I haven't spent much time on it. I've cleaned and synched my carbs and it hasn't helped. I know my spark plugs are pretty grungy and next time I do valves I'm going to replace them but I doubt that's got anything to do with it. I guess I could try leaning out the idle needle and see if that helps but it runs so well otherwise I don't want to make things worse before they get better.

Matt
 

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Use the KISS principle here, ie Keep It Simple etc.

I'd hold off on dropping $$ for a black box until you can prove that the one you have in there is definitely kaput. You wouldn't believe how much mix and match you can get out of the boxes with greater and lesser degrees of performance. EG, my 93 1100 water pumper kicks ass with a factory WSB oiler 750 box. As well, I'll be using a Katana 600 black box on mine for a NON performance experiment.

Damned near all of that low end stutter can be traced back to CV carbs with factory set pilot jet sizes still installed. Just go up a size and see how much the 'up to 2000' cleans up.

Small rant: lots of guys get their minds fried fucking with the emulsion tubes/needle clip positions etc from their Dynojet kits on account of the owner/designer does not feel the pilot circuitry has any play in the works 'since the bike can run fine without any of the other carb circuits'. Well, that's very nice, but unfortunately, things don't happen in zero time within a CV carb. While the thing is coming up on the mains etc, you get an analog, not digital result, ie the pilot circuit is still in the mix for about 1000 rpm into the main circuit 'turn on'.

That's why so many guys get great results from dynojet installs done by pros in a dyno shop and so many others are just fucked trying to get things going by themselves.
 
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