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Discussion Starter #1
So a little while ago there was a post about average top speeds for a given bike. A couple of you said your CB750s would take you well over a 100mph. Ive been riding mine around and it seems to be running fine. Lots of power on the bottom but it seems to wind out quick. When im in 5th doing 60-70mph im over 7k on the tach. To do 90 or so im at the red line 11k. Ive not owned one before, but was expecting more out of it. Should i be getting more out of it?

My CB750 Project:
http://www.caferacer.net/forum/topic.asp?TOPIC_ID=4739
 

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They should be good for at least 110mph on a reasonably fresh motor. Maybe the gearing's been changed on yours?

I've been thinking about caffing a CB750 and spent a while on this site........

http://www.cb750cafe.com/

You've probably seen it all before, but the stuff he does is superb!
 

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How worn is your clutch? sometimes when the clutch is worn, not adjusted properly, or the motor is hopped up the clutch will slip at high speed. A good litmus test for this is to get on the highway in top gear at 50mph and then whack the throttle wfo. If the bike revs up faster than it accelerates your clutch is slipping and you need to attend to that. A slipping clutch can cause all sorts of other problems with the pressure plate and flywheel.

Count the teeth on your rear and front sprockets. post the number.

My cb750 is between 4K and 5K at 60-70 mph.

A good upgrade for your bike is to get fresh honda clutch steels and fibers and barnett springs.


Edited by - geeto67 on Sep 12 2007 10:10:08 AM
 

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yeah, thats way too many rpms. i get around 5k at 65mph. and you should be having rods flying out of your engine if you are taking it to 11k rpm. since redline was around 8k rpm factory.

'72 cb750
'76 cb550
 

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Discussion Starter #5
the guy i got it from said it had an aftermarket cam in it, and i was told this would allow for a higher rpm band. ive burried the needle a couple times 11k+ and had no problems.

I havent noticed a lag in power or felt the clutch slipping, but its possible, i dont know if it would feel like it does on a car when the clutch goes out but if it does then thats not the problem, but ill find a way to check.

it could be a gearing thing, ill count the teeth and post the number, i dont know what factory was.

My CB750 Project:
http://www.caferacer.net/forum/topic.asp?TOPIC_ID=4739
 

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Discussion Starter #6
i counted the rear sprocket and it has 48 teeth, i looked around online and found that this was factory so im assuming the front sprocket is stock too, but i dont have time to pull the cover off yet. even if the front wasnt stock wouldnt it really make that big a shift in the power band. from what you guys are saying im 2-3 k over what i should be 60/70mph cruising.

My CB750 Project:
http://www.caferacer.net/forum/topic.asp?TOPIC_ID=4739
 

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K0 had a redline to 8500rpm
K1-K6 had a redline at 8000 rpm
F/F1 had a redline at 8500 rpm
K7/K8 had a redline at 8500
The 76 K6 and F1 were the only ones to have a light green face
Some of the early dark green gauges have faded and appear to go blue

here is the sohc gauge spotters guide:

http://www.sohc4.us/forums/index.php?topic=6961.0

Something tells me you have cb550 gauges on a cb750. If that is the case the cb550 and 750 have way different tach drives and are not interchangible. At idle they will be close to accurate but at WFO they will be waaaay off. The later cb550 big gauges (75 and up) are very similar to cb750 gauges and it is easy to get them confused.

the closest I could find to what your gauges should look like are these k2 gauges:



The cb350F and 400F had 10,000 rpm redlines and also use different tach drives from the cb750. The gauges are smaller than stock but will still fit the mounting bracket. The big 550 gauges look almost identical except for the 9500rpm redline.
 

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yup - 1976 cb550 speedo and tach. I didn't even think to ask about the speedo but all SOHC cb750 speedos read up to 150mph, the 550s read up to 120. You can see how similar they look to 750 gauges but they are not.

The speedo should be accurate, almost all jap bikes use the same oddball speedo ratio (2240:60), but the tach is way off. cb750 tach ratio is 4:1 where as the 550 ratio is somewhere in the neighborhood of 3:1 or some fraction there of. Either way it reads way higher on a 750 than accurate.

my advice to you, get the correct tach pronto. who knows what kind of damage you can do without knowing where the proper redline is.
 

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Discussion Starter #14

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sorry I had that reversed. The mini-gauges work ok. If that is really the look you want. I had a set from JC whitney and they fell apart on me but they were the cheap-o ones. those look a little better.

If you are going right to an aftermarket gauge, I would get a dwell meter and check the rpms electronically. Every dwell meter has the setting to do this and a good quality one costs $30 from sears. Plus you can use it to set the dwell on the cb750 points which is always good.

you can go to an autometer tach as well (or any other electronic tach for a wasted spark ignition) but those are pricey.
 

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Discussion Starter #16
i think im gonna go with the mini gauges, im gonna get clip ons and i think the stock gauges look too bulky with the lower bars. ill check out the dwell meter.

i am leaking some oil from my clutch cover, it leaks a little and itll smoke a little from the leakage burning, it seeps a little on and off depending on how long im running the bike, should i be that worried about it?

My CB750 Project:
http://www.caferacer.net/forum/topic.asp?TOPIC_ID=4739
 

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while the clutch cover gasket is one of those few gaskets you don't have to pull the motor to replace, when you buy your gasket kit and see all the pretty new leak free gaskets then you will want to install all of them.

My advice? if the motor is not currently leaking any oil from the cylinder block area, then buy a gasket kit and just replace the clutch gasket. If you are so inclined, when the first snowfall hits you may want to pull the motor and replace all the gaskets, but be forewarned, the little seals inside the block for the oil return are a huge pain in the ass. but for right now do the days worth of work and just replace the clutch cover one.
 

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gaskets? what the hell are they? i grab a tube of my trusty 3m brand clear sealant for EVERYTHING that needs to be sealed. including exhaust manifolds and turbos. that stuff is incrediable and you can't see it because its clear. just wipe away the excess.

'72 cb750
'76 cb550
 

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Most japanese engines are put together with hondabond, yamabond, or kawibond. however there are still some parts that have gaskets or orings. Typically SOHC cb750 oil pans have a gasket and you don;t really want to put sealer in an oil pan or a carb float bowl. a) it makes it hard to get off and B) you don't want any excess mixing with those fluids and gumming up the works.
 
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