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Thread: derestricting gsxr 750 ( help needed)

  1. #1
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    derestricting gsxr 750 ( help needed)

    got an 86 jap import gsxr 750.
    have taken the restrictions out of the pipes put another can on .
    but does anyone know if there are any other restrictions on these bikes?
    any help appreciated
    cheers

  2. #2
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    I don'r know your specific bike but if its the same as my zxr750 then the restrictions will be.
    1) speedo /rev counter only allowing the bike to go to 190k and less than max revs in top gear. --There is a little black box that solves that problem.
    2)different cams and cam angles - may be able to dial in better angle
    3) different innards in the cdi Box fixed by getting a kiwi cdi
    4) different jetting in the carbs. Possibly in your case different size carbs.
    5) may not apply -2 pickups in the airbox in kiwi model only 1 in jap model.
    6)restricted inlet manifolds -can be opened up as theyre only rubber.
    To see a life newly created.To watch it grow and prosper. Isn't that the greatest gift a human being can be given?

  3. #3
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    Quote Originally Posted by XJ/FROSTY
    1) speedo /rev counter only allowing the bike to go to 190k and less than max revs in top gear. --There is a little black box that solves that problem.
    Where's this little black box/what does it do? I'm pretty sure mine got some sort of limiting and I wouldn't mind removing it if it doesn't cost too many $$$$
    Life is difficult because it is non-linear.

  4. #4
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    Quote Originally Posted by dhunt
    Where's this little black box/what does it do? I'm pretty sure mine got some sort of limiting and I wouldn't mind removing it if it doesn't cost too many $$$$
    It's a good question. Does your bike rev freely and strongly and then "hit" a speed limiter at 180km/hour or so or does it lack the puff to go any faster? I expect it will be the former. What I figure is that the "mechanical" (like different cams or smaller carbs or different jetting etc) restrictions are going to limit only horsepower, not limit your speed to a certain maximum such as 180 but except to the extent that limited HP will limit top speed (even a limited HP GSXR750 has to be good for over 180km unless the gearing is way low). A speed restrictor has got to be electronic (forgive me if I'm mistaken but I can't see any other way) so if your bike hits a limiter at a certain speed I would be looking at electrical system and particularly at the CDI. There is a supplier of NZ made aftermarket CDI's for these bikes (check http://www.trademe.co.nz/Trade-Me-Mo...n-17217428.htm). Perhaps you should ask that seller about the issue of speed limiters. Another option is to beg/borrow a CDI off a NZ new (unrestricted) GSXR and see if that solves the problem.

    Do think about gearing too. It should be spinning at something like 5000rpm in 6th at 100km. If it's revving much higher you could look at going to a bigger front sprocket by (say) 1 tooth, and that will theoretically raise your top speed as well (although of course doesn't actually do so unless the speed limiter is disabled and you have the HP to push the bike to the red line in 6th
    Kerry

  5. #5
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    Quote Originally Posted by kerryg
    It's a good question. Does your bike rev freely and strongly and then "hit" a speed limiter at 180km/hour or so or does it lack the puff to go any faster? I expect it will be the former. What I figure is that the "mechanical" (like different cams or smaller carbs or different jetting etc) restrictions are going to limit only horsepower, not limit your speed to a certain maximum such as 180 but except to the extent that limited HP will limit top speed (even a limited HP GSXR750 has to be good for over 180km unless the gearing is way low). A speed restrictor has got to be electronic (forgive me if I'm mistaken but I can't see any other way) so if your bike hits a limiter at a certain speed I would be looking at electrical system and particularly at the CDI. There is a supplier of NZ made aftermarket CDI's for these bikes (check http://www.trademe.co.nz/Trade-Me-Mo...n-17217428.htm). Perhaps you should ask that seller about the issue of speed limiters. Another option is to beg/borrow a CDI off a NZ new (unrestricted) GSXR and see if that solves the problem.

    Do think about gearing too. It should be spinning at something like 5000rpm in 6th at 100km. If it's revving much higher you could look at going to a bigger front sprocket by (say) 1 tooth, and that will theoretically raise your top speed as well (although of course doesn't actually do so unless the speed limiter is disabled and you have the HP to push the bike to the red line in 6th
    Thanks mate, I'll look into it. I think it could be a combination of things including gearing as 6th gear@100km/h=6000rpm. It also feels like there is a soft rev limiter that starts cutting in maybe 9.5-10rpm as stops pulling so hard. Would a new CDI affect this at all??
    Life is difficult because it is non-linear.

  6. #6
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    mine sits on about 5000 at a 100 in 6th .put a different sprocket on it last time i done the chain and it does make a difference.

  7. #7
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    Quote Originally Posted by dhunt
    Thanks mate, I'll look into it. I think it could be a combination of things including gearing as 6th gear@100km/h=6000rpm. It also feels like there is a soft rev limiter that starts cutting in maybe 9.5-10rpm as stops pulling so hard. Would a new CDI affect this at all??

    You could ask the Hyperpak people their opinion. That's one possibility. And/or
    another KBer (Sedge) has got a Jap market GSXR750 (180km speedo) that he bought off me (silly fella ) and it has a Hyperpak CDI on it. When I owned it I never tried out the speed limiter but he, being younger and bolder than me, might well have done so by now. You could maybe PM him in case he's got any insights? If he sees this (nice fella that he is) he might post something...are you there Sedge?

    If I remember the standard gearing on the GSXR750 is 14/42 (correct me if I'm wrong). If your bike is revving at 6000rpm in top at 100km/hour and has that gearing then I suspect your internal gearing is different from NZ market bikes. That seemed to be the case with the GSXR750 I owned although it was confusing because the rev counter wasn't reading accurately. Solved easily enough with a slightly larger front (up 1 tooth is enough) or smaller rear (down 2 or 3 teeth) but it will make it slightly harder to launch and you'll need to be up and down the gears a bit more to keep it on song.

    Running out of puff at 9500-10000? I would have thought that it would rev quite happily to red line in the lower gears at least . You should get a real "kick in the pants" at about 7000 when it comes on the cams. May be a tuning problem more than a restriction but I could be wrong.
    Kerry

  8. #8
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    i rang hyperpak and they said their ignition system will advance by about 5 degrees and is a more even curve.
    my bike has been changed to make it breathe better and the guy says i will notice a big difference in it. if i use the ignition deveice for my bike.

  9. #9
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    Quote Originally Posted by soundbeltfarm
    i rang hyperpak and they said their ignition system will advance by about 5 degrees and is a more even curve.
    my bike has been changed to make it breathe better and the guy says i will notice a big difference in it. if i use the ignition deveice for my bike.
    Hmmm might try getting one later on in the year as it seems the way to go. Do you need to retune your engine at all, or is just a drop in replacement?
    Life is difficult because it is non-linear.

  10. #10
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    Quote Originally Posted by dhunt
    Hmmm might try getting one later on in the year as it seems the way to go. Do you need to retune your engine at all, or is just a drop in replacement?
    Sorry d hunt--I diddnt go back to this thread--Um the lil black box is something you can buy -as i understand it it allows the bike to rev out properly in top gear and run past the 190km/h mark. although Im not certain about the speed bit.
    To see a life newly created.To watch it grow and prosper. Isn't that the greatest gift a human being can be given?

  11. #11
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    Quote Originally Posted by dhunt
    Hmmm might try getting one later on in the year as it seems the way to go. Do you need to retune your engine at all, or is just a drop in replacement?

    he said just put the thing in and she'll de sweet .

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