750 f/b reinstated

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Davy

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Dec 12, 2009
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Hi Folks

After 8 years i have got my f/b running again it went off the road due to white van man doing a Uturn infront of me and although it only suffered light damage my knee didn't .I was not happy with the repairs done by the ins company and stripped down to repair but never got round to it till now. New mikuni /belt drive /close ratio gearbox .the lot!
put petrol in the new 8yrs ago tank started no problem sorted timing e.t.c had to leave for a week started again and it ran like a pig the carb was full of resin there must have been a spot of fuel left in tank when it was put away ! i cleaned carb removed tank put on my lawnmower tank and got it running again have found that i need to slip clutch on pulling away i think this is caused by the gearing ie. belt drive/close ratio gearbox/21t gear sprocket.Would dropping down to the 19t sprocket make a big differance?



750 fastback 1971 bmw k75s honda cb1300
 
L.A.B. said:
swooshdave said:
Why did the insurance company do the repairs?
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Why would you consider that to be unusual?
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Are they familiar with repairing Nortons over there? If so they have amazing skills for an insurance company.

If you mean they picked the shop and the shop fixed the bike, well, who did the work?
 
swooshdave said:
If you mean they picked the shop and the shop fixed the bike, well, who did the work?
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If you are going to be pedantic about it :roll: yes. I'm sure most people would have understood what he meant, after all, it's the insurance company that's ultimately responsible for getting the repair work done, the repair shop is merely a subcontractor.
 
Welcome to the forum, Davey.

If the gearing was right before, it shouldn't need to be changed now. (I would think).

Maybe a clutch cleanup?
 
grandpaul said:
If the gearing was right before, it shouldn't need to be changed now. (I would think).
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With a new "belt drive" (often higher ratio) and a "close ratio gearbox" added, the gearing is unlikely to be the same as it was before, especially in the lower gears.
 
Hi folks

just to clear up a few points the ins company allocated the repair to a local company who did not have a clue about commandos . The gearing was fine with std primary and std g/box and 21t g/box sprocket Now that i have belt drive and (RGM) c/r gears i will need to drop down to a 19t g/box sprocket as the gearing is now a bit to high although 1st is now a looooong gear

Davy
 
Sorry, misunderstood the "running like a pig" was AFTER the change-over to belt drive.

Agree with L.A.B. regarding gearing change needed...
 
Hi again

The running like a pig was the resin from the tank clogging the carb (ethinol in the petrol) the engine runs fine now just got to sort the gearing (smaller G/Box sprocket) Sorry about any missunderstanding
 
IMHO the close ratio gear set is a BIG mistake on a street bike as you have found out. I would find a new owner of this gear set and go back to standard gear set as you will have a lower first gear. what is the RGM belt ratio from stock? if it is over driven from stock that is a good thing and you will need to adjust the final drive to get back to where you were.
 
Id fit Cork Clutch plates . :p :roll: :lol: . or a 5-speed .

First will be about where second was with a close box .
if its just for ' street fighting ' lowereing top wont do
a lot of harm . But if youre setting the Edenborough to
London speed record , youll need the tall gearing .

Schnafliner did six speeds , but no kick start .Quaife 5-speed
as per 72 P.R. is the go , but ive seen one that broke a main shaft .

Triumph 5 speed will go in a pre-unit trumpy box , if youre sacriligious.
 
G'day Davey, Welcome aboard.
Is the motor standard, or have done some nice things in there, the reason I ask is
that the single Mikuni will tend to run out of steam at around 5,500 -5,800 revs, ish, and as you have fitted the C/R Gearbox
I am assumeing that you like to twist that throttle right around more often than some.
I know nothing of the gear box so you could inform those of us that don't already know.
Is it four speed, which would explain the high bottom or is it five speed.
21 teeth down to 19 teeth is a pretty fair jump in my opinion, but with the extra gearing caused by the belt drive
then it's understandable and probably right.
I think from memory,... One tooth on the front is only worth about 400 - 500 revs in top gear so it's not much at all in first.
I believe that altering primary gearing, has much more effect on Engine characteristics than changeing Secondary gearing.
Also what clutch. I fitted the Barnett clutch to mine with the rebiuld and up to 22 Th sprocket, and the Barnetts seem to be
a lot more reactive than the standard clutches, which makes it a little harder to get going with the wife on the back.
Anyway get some photos up for us to see what you've done, it sounds all good.
AC.
 
Hi folks

THe final gear ratio is the same as std the first is longer (higher) so i will try 19t g/box sprocket and see how it goes. I am not too bothered about high top speeds as i prefer the twisties and hoped that the c/r box would help keep it on the boil 4 speed .The engine is fairly std ( knackerd knees) the bike had a 19t but i felt it a bit revvy and put on the 21t as it was my main bike if all else fails iv'e still got the old bits
 
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