Stupid question regarding RS carbs on a 750.

[Upshotknothole]

I'm pretty sure I already know the answer to this, but asking here to save myself a days hassle trying it and returning it back to stock. I've got a GSXR 750M/N with the stock carbs and a warn to hell dynojet kit in them. Bike runs ok, but only gets like 30MPG on the freeway, emulsion tubes and needles are shot, usual stuff. I also have a nice clean set of Mikuni RS38s that I know are too big for the bike, but just how much too big are they? I had a J/K 748 years ago with RS36s and that bike was amazing fun, as long as you kept it over 5K. Every time I see 38s listed as being compatible for the 750s, I start to wonder a little...

Just how bad will the bike be on the street with RS38s? I know I should just buy RS36s for it, but I have other priorities right now. I also don't care about bottom end, I've got a 7/11 for that. I also have an 1127 sitting on the bench that could be used once I go through it, but I really like having a 750 again.

[Lachie04]

I had 38's on my 816 Dot head motor and loved them gave around 17k/l + (40+ mog) normal riding and were pretty good. Loved the fine control in mid range and for quick take off a little rev to around 2000 to get the air moving would pull sensationally I always thought they were a little big but they were destined for a bigger engine in the end so didn't mind .  If  just building a 750 then I would probably go 36's but they will work 

Edited May 20, 2022 by Lachie04

[Upshotknothole]

Cool, I'll throw them on for the weekend and see just how stupid they are. Thanks for the insight.

[Lachie04]

I dug out final jeting solution for mine after a few rounds on the Dyno it was border line 132.5 - 135 on the main jet anything to much bigger would over rich the engine at WOT  I did change the air jet to  09 just to play round with some slow speed richness but don't think it was really m necessary and changed pilot jets but main jet def start round 130 up 

 

[Upshotknothole]

Thanks! I was gonna start on it today but can’t find the throttle tube for my push pull throttle. I’ll check my carbs and see what they currently have in them. These are a spare set that I’ve never ran and can’t remember where I got them. 

[Upshotknothole]

Finally got around to checking my carbs. Currently have 135s in them. My stock BST38s started being really slow to return to idle yesterday if I didn’t let the throttle snap closed, like not really dropping RPM when rolling off while shifting. So thinking I might finally go ahead and swap these in tomorrow. If they’re too much, I’ll stick an 1127 into the bike next week. 

[davecara]

Please keep reporting back! Ive never used RS carbs andf I'll have a set of RS38's coming my way in a few weeks. Just need an 1127 to bolt them too!

[Upshotknothole]

6 hours ago, davecara said:

Please keep reporting back! Ive never used RS carbs andf I'll have a set of RS38's coming my way in a few weeks. Just need an 1127 to bolt them too!

My 7/11(that I need to put back together) has RS38s, you give up some bottom end around town, but get into the twisties or a long open road, and they come alive. Velocity stacks and RamAir filters are the way to go with them. I’m expecting my 750 to be nothing but top end with them if I can get it running.