SOHC.co.uk Forums > CB750

Under-geared F1?

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StealthDJ:
Hi all,

After a number of years since my last one (an F2), I’ve come into ownership of another SOHC 750, this one a 1976 F1 that had been dry stored for 20 years, but with a largely unknown history of modifications.

I’ve sorted the obvious issues - rotten exhaust, worn out clutch, seized brakes, plus a few others and last weekend did 240 miles over two days, mostly motorway work.

The thing that struck me, especially from what I remember of my F2, is that it feels very under-geared.  The Delkevic exhaust isn’t exactly quiet, but 70mph (around 5k rpm) feels like I’m thrashing it, whereas my memory of the F2 is that it’d pass 100mph with relative ease.  I’ve checked the drivetrain though and it’s running 18/48, which appears to be standard.  Should I be taking a couple teeth off the rear sprocket, or is this normal?

Also, from the section of the trip where my wife was following me, it seems what shows as just over 60mph on the speedo is probably closer to 70.  Wondering if I might have the wrong speedo/drive, or if it’s more likely that the internals are gummed and a refurb is required…

Bryanj:
There is only one speedo drive for 19 inch wheels so its likely gummed, as long as rear wheel is 18 inch stick with standard gearing or it wont pull away at all well

Trigger:
Unless you have a 16 inch rear wheel at, 4.000 rpm in top gear your clock should show 60mph  ;)

Spitfire:
My 76 F1 speedo is 7 mph fast at all speeds, when I first got it back on the road I followed my wife who was in our car through Liverpool and was amazed at the speed she was going past speed cameras, so we checked the bike speedo at 30, 40, 60 and 70 and found it was consistantly fast.
I've had the bike since new so it is fairly bog standard apart from cosmetics.

Cheers

Dennis

Skoti:
Previous owner fitted a smaller rear sprocket to my 1976 F1, it pulls 60mph @ 3500rpm.
It's nice and relaxed and pulls top gear fine when two up touring loaded with camping gear etc.

So yes I can recommend a smaller rear sprocket.
Hope this helps.

(Photo taken on route to Honda4Fest earlier this month)


   

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