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94 Cb750 maxes out at 80mph

Smolina

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Hi everyone. I have a custom cafe racer with a stock engine running on 135 Jets into stock carbs. Bike runs great but fifth gear she is basically maxing out at 80 so mph. The sprockets are not factory and I believe are smaller in front and back which gave it more acceleration but I don’t know why that would affect rpm hitting high at 80mph in 5th gear. Any tips??
 
Hi everyone. I have a custom cafe racer with a stock engine running on 135 Jets into stock carbs. Bike runs great but fifth gear she is basically maxing out at 80 so mph. The sprockets are not factory and I believe are smaller in front and back which gave it more acceleration but I don’t know why that would affect rpm hitting high at 80mph in 5th gear. Any tips??
If it's a '94 CB750 Nighthawk, the stock sprockets are 15 and 38 and should yield a top speed around 115 @ 8500rpm - or thereabouts
 
Yes I believe it is running on 14 and 40. Do you think that would explain top end speed? Torque is definitely nice though.
 
Do you know of anyways to keep the top end high and still raise the torque?
I'm not real familiar with that model or the mods that have been made, but I would think stock gearing would be better for all-around riding and should have plenty of low-end torque to pull that gear.
 
Hi everyone. I have a custom cafe racer with a stock engine running on 135 Jets into stock carbs. Bike runs great but fifth gear she is basically maxing out at 80 so mph. The sprockets are not factory and I believe are smaller in front and back which gave it more acceleration but I don’t know why that would affect rpm hitting high at 80mph in 5th gear. Any tips??
Smaller back sprocket less acceleration
 
Are there other ways to gain top end besides changing sprocket and losing acceleration?
The upper rpm the motor was designed for (redline) is the limiting factor and most folks prefer to cruise at a mid rpm. Many engine modifications (except racing extremes) are aimed at gaining better acceleration and torque so one can run taller gearing. Old adage: How fast ya wanna go, how much $$ ya got?
 
well I believe a 1994 rc42 is supposed to go 125. Given her age regardless of work done to re do the engine I would expect her to go a bit less around 115 120 but now with the sprocket change to gain torque which is now 14-40 I would still like to gain top end without hurting the torque. She is basically maxing out at 80 now. I’m not expecting her to go 150 or anything but I would like around factory range or 130. I am just unsure how to go about it.
 
It is a trade off between torque ( acceleration) and top speed. I found the stock gearing of 15 front 38 rear to be the best ride. I never go above 75mph.

you need to bore that baby out to at least 1000cc then you will be happy!!!
 
It is a trade off between torque ( acceleration) and top speed. I found the stock gearing of 15 front 38 rear to be the best ride. I never go above 75mph.

you need to bore that baby out to at least 1000cc then you will be happy!!!
Haha I was just looking into that. I’m thinking of first trying to change the rear to 38T and keeping the front at 14 and hoping to get a little more at top end. As far as getting a bore kit. I only know one that works with rc42 and it is a lot of mixed parts and gets it to 815cc but I’m not sure how much more top end that’ll give.
 
Are you sure theres no clutch slip...either from maladjusted cable/incorrect oil...?
Miles per hour vs rpm in top gear should b linear....(in the absence of slip)....

Also are.you running regular wheel and tire size?
 
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