Jap import GSXR750G

[kerryg]

I have a Japanese domestic market model (180km speedo) GSXR750G and I wonder if there is anyone out there can shed some light on how they are restricted. I know from different sources that the domestic market model had (1) restricted HP (down about 20+HP on the unrestricted ones) and (2) as well as a speed limiter. I believe the speed limiter may be bypassed by fitting an aftermarket CDI...but I'm not even 100% sure about that, but does anyone know how engine can be de-restricted and/or with certainty how to by-pass the speed limiter? I know the easy answer is to throw the engine, if not the whole bike, away and get a better one but that's not an option!

And another question: I bought it as a non-runner and having finally got it back from the mechanic I got to ride it on the weekend for the first time and found out that it is geared really low (6500rpm in 6th is 100km/hour), therefore redline at 11000rpm gives a top speed of 170k. I was not well pleased! As this is (was?) going to be my track day bike I need more top speed, and so I'm thinking of changing the gearing. Currently has a 14 tooth engine sprocket and 42 tooth rear. My rough maths suggests I need to raise the gearing about 20% which means up 3 teeth on the front or down 9 on the rear!!!

I'm wondering if anyone else has had to make a gearing change of this magnitude on a similar/the same bike and would value any comments before I start hurling yet more money at it.....

[F5 Dave]

A quick look at a sprocket site (AFAM) shows that 14/42 is std gearing. I would have thought a GSXR of that vintage should be able to cough its way through to 200 easy enough (restrictions aside). 6500 at 100 sounds about 1-2000rpm too high though. Sure someone hasn’t slipped a 400 engine in there??

Something does not compute. Perhaps the gauges are suspect? The rev counter? On some bikes the restriction is in the speedo so someone might have been in there tampering & stuffed it (ZXRs you add a resister somewhere to fool the connection back to the CDI.

[White trash]

My Dad had a 750G back in the day (Where I got my Gixxer addiction from) and it was good for a real 247kph with Yoshi pipe and cams on Std gearing.

"OldR" has a Gixxer7F and its pulling about 5000 at 100kph.

Normally, in those days, they restricted the power through smaller carbs, cams and timing. They used to be really easy to get second hand parts from as they were a popular bike to crash so I cant see you having too many problems.

Go to www.gixxer.com and see what others have done to unleash the fury.

BTW, nice bike.

[kerryg]

A quick look at a sprocket site (AFAM) shows that 14/42 is std gearing. I would have thought a GSXR of that vintage should be able to cough its way through to 200 easy enough (restrictions aside). 6500 at 100 sounds about 1-2000rpm too high though. Sure someone hasn’t slipped a 400 engine in there??

Something does not compute. Perhaps the gauges are suspect? The rev counter? On some bikes the restriction is in the speedo so someone might have been in there tampering & stuffed it (ZXRs you add a resister somewhere to fool the connection back to the CDI.

Dave, thanks for the comments. I suspect it might be that the internal gearing on this bike is different (geared lower). The front and rear sprockets currently fitted are, as you said, pretty much the norm. I am pretty sure the rev counter is reading right just from a seat of the pants perspective. It pulls happily to red line but is fair howling, and it certainly does feel like 6500rpm at 100km, so I'm reasonably confident the tacho is accurate, and judging from my speed relative to other vehicles I think the speedo is reading correctly. If it's out at all it's not out by much.

I'm going to try a couple of teeth up on the front sprocket and see what difference that makes. Then I'll look at releasing some more HP (somehow...)

[kerryg]

My Dad had a 750G back in the day (Where I got my Gixxer addiction from) and it was good for a real 247kph with Yoshi pipe and cams on Std gearing.

"OldR" has a Gixxer7F and its pulling about 5000 at 100kph.

Normally, in those days, they restricted the power through smaller carbs, cams and timing. They used to be really easy to get second hand parts from as they were a popular bike to crash so I cant see you having too many problems.

Go to www.gixxer.com and see what others have done to unleash the fury.

BTW, nice bike.

Hi WT. Thanks for your info. I owned a stock NZ new GSXR750H last year (wish I'd never sold it...another story) and it sat at 5000rpm at 100k, just like you say, and it was good for well over 200 (I never tried to redline it in top but I'd guess 240 or so). Went like a much newer bike really. So I am puzzled...anyway I'm going to change front sprocket to a 17 (up 3 teeth!!!)and see how she rides. Might be like a RS125 to launch though....

[F5 Dave]

Yeah the internal gearing change would have to be either primary vs clutch from another model (v.unlikely) or someone has fitted a close ratio racing box. Also unlikely on a jap domestic bike I would have thought.

So you’ve launched an RS? Esp. the older less powerful ones, you paddle while screaming the engine introducing mm by mm of lever travel until you get to ~ 80k & then let go of the last little bit & it bogs –What? There’s more?!?!??

[kerryg]

Yeah the internal gearing change would have to be either primary vs clutch from another model (v.unlikely) or someone has fitted a close ratio racing box. Also unlikely on a jap domestic bike I would have thought.

So you’ve launched an RS? Esp. the older less powerful ones, you paddle while screaming the engine introducing mm by mm of lever travel until you get to ~ 80k & then let go of the last little bit & it bogs –What? There’s more?!?!??

Nah I haven't personally launched a RS125 but I've watched them being launched (stop slipping the clutch by about the time they get to Castrol)...

I agree with you about the internal ratios. Neither very likely, but it seems the only explanation if my gauges are reading correctly. Anyway just now ordered my 17t front sprocket from Colemans so here's hoping it works