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Discussion Starter #1
I had a problem with one of my CB750's where I couldn't redline it in top gear on the street. (yea - I already know I should do that)

Previously I had geared the bike to bring down the R'rs on the highway and I was thinking I had gone a little overboard on the gearing and that was the reason why I couldn't get more than 7500rpm's out of it in top gear. The bike would redline in all gears except 5th and ran pretty decent.

So I spent most of this past Saturday going through the bike and giving it a good tune up. It was due for an oil change anyways so I also changed the plugs, set the valve lash and cam chain and checked the timing. (I have electronic ignition in it)

After I got done doing the tuneup, I tested the bike on the highway. Now the bike will easily redline in 5th. I'm now thinking about throwing more gears at it to reduce the R'rs even more.

I guess the lesson learned here is even if the bike seems to be running decent - it still may need to have a schedule tune up.
 

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If it will red line in 5th, it needs more gearing for highway use.
That must be a real good motor or gearing was set for drag racing?
 

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Stock gearing on a k6 or earlier will be over 130mph at 8500 rpm. What's your final gearing now?
 

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Discussion Starter #4
The gearing I'm running now is either 17X45 or 18X45. (I cannot remember the primary size used without looking) Stock gearing would run the bike up to 125 downhill in a prone position so I don't think the 130 at 8500 rpm is that accurate. Redline is at 9500rpm but I don't run it more than 9000. As far as the motor goes - it's basically a stock 78 F2 motor with M29 smoothbores with a Kerker pipe with a comp baffle. I believe with the carb and pipe setup really helps this big valve motor run pretty decent. With this gearing it runs 160Kph (100mph) at 7,000rpm.

By no means is it gear'ed for the track. Last year I took it to the track and with stock carbs I ran 92mph through the trap at the very top of 2nd gear - I was toying with the idea of taking it back this year but change out the gearing to something like a 14X52. With this gearing I should be able to get into 4th at the trap. Before I do that I will need to upgrade my clutch as I don't think my stock clutch would run good with this gearing. My ET was a high 13 which is not that impressive. The gear change would bring that ET down to mid to low 12's and change my mph to just over 100. That really not too bad for an old fat guy.
 

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Oh, I was talking about gearing on the k6 and earlier.

Is it an 18" wheel? Because 18x45 puts you at 149mph at 9000 rpm with an 18" rear wheel.... 17x45 puts you at 140...
 

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Discussion Starter #6
Yes it is an 18" rear wheel - 19" front. I really doubt I was going anywhere near that fast but I can say my sunglasses got ripped off me when I tried to duck down below my windscreen (1/4 fairing style). What would be the max speed with a 15 or 16 primary gear? I'm sure the rear sprocket is a 46 - I checked this morning. As I said earlier, I would have to look again to see what I used as a primary. I'm thinking it's a 17 but I could be wrong and it may be a 15. I do remember making sure it was an odd number because the rear sprocket was an even number. I had read somewhere where the two sprockets should be even/odd or odd/even. I'm pretty sure I'm following that rule.

149mph - that would be bad ass but I don't think I am anywhere near that speed. I do cross the 100mph mark at 7000 rpm - that's verified.
 

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Carbs and exhaust [8D]
Nice ;)
Completely stock, they won't go over 125mph (worked at a Honda dealers when they were launched, remember it slightly, test riding the demo bike to break it in in pissing down rain :D
Forks are a bit flimsy
 

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quote:Originally posted by mlinder

What's your rear tire?
It's the round rubber thing at the back of the bike :D :D :D
 

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quote:Originally posted by crazypj

quote:Originally posted by mlinder

What's your rear tire?
It's the round rubber thing at the back of the bike :D :D :D
No, that's a Tyre.
 

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Discussion Starter #11
I'm using a 18x130/90 Shinko tire on the rear mounted on a Henry Abel mag rim. I agree on the 125mph max speed mark...
 

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quote:Originally posted by bmartin

I'm using a 18x130/90 Shinko tire on the rear mounted on a Henry Abel mag rim. I agree on the 125mph max speed mark...
16x46 with a 130/90 is around 135mph at 9 grand.
 

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Discussion Starter #14
135 - If that's an accurate number - Maybe that's why my glasses got ripped off my face... BTW - 18" rear wheel not 16"...

TrialRider - Nice buggy you got there. I'm planning on running this bike and another cb750 w/turbo at Loring next Aug. Records - who knows - I'm just going to do it for the heck of it. I'm under no illusion of breaking any real records. The last record I saw for a semi-stock CB750 was 137.## mph - but that record is like 10 years old. So who really knows what a/any record might be for a 750cc CB750. May be Geeto will chime in and say what that might be.
 

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I didnt say 16" rear wheel, I said 16x46 final gearing. :)

I've had a k0 at around 130, maybe a little more. Geared properly, though. About 9500rpm in 4th. I liked being able to cruise between 80 and 90mph at about 5200rpm. 90mph puts you are about 6krpm with 16x46. Find out your front sproket, please.
 

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Discussion Starter #16
Gotcha - I'll check it out tonight and let you know. I do believe I'm seeing 90 at 6K myself - so I must have 16X46 gears but I'll double check.
 
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