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CB750K0 Carburettor Problems

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Steph550:
Hi all,

My other half has a 1970 CB750K0 which has been causing problems for a while now, it looks stunning but has had consistent carburation problems which we can't solve.

The bike is reluctant to pick up at RPMs less than 3500 - when the throttle is opened it initially dies and then suddenly picks up. There is a considerable amount of hesitation when riding at around 30-40mph. It is also a nightmare when trying to pull away, for example at a junction, he has to rev it and ride the clutch to stop it from dying half way through pulling out. However, the tickover is very sweet, and at higher RPMs (for example, cruising at 50mph plus) it picks up fine.

The carbs have been balanced several times now, just after they have been balanced it runs beautifully, but once it's been left for ten minutes it's all over the place again. It has been checked for air leaks (by spraying fluid onto the engine to see if it temporarily improves) and there are none. Plugs all look perfect.

The bike has been restored to a very questionable standard by a 'professional' company, and it has taken 9 months to even get it running and on the road. However we are now really stuck with the carbs. They have had new carb kits fitted, but we are beginning to think that the carb bodies themselves are worn, and the bike will never run properly with these carbs on it.

Has anyone else experienced anything like this? My other half is now looking to source another set of carbs for it, if anyone has any they would be prepared to part with..? :-\

Cheers,

Steph..

Bitsa (Ralph Wright - RIP):
Steph,
I can not help you with your problem at the mo but I am sure the other k0 owners will come to your rescue.Though they had four cables the rest apart from jetting etc can not be much different between the rest of them.If at a last resort you want another set I do know where I can lay my hand on some albiet there condition is unknown.
Cheers
Bitsa

Trigger:
It sounds like they are sucking air or a load problem. Will sleep on it and talk to some carb racing engineers tomorrow and get back to you Steph.

JamesH:
Have you tried running the bike on a later set of std carbs with the twin linkage? At least a known good set of carbs would tell you if yours are suspect, Did the bike come from the dealer in Ireland that have ceased trading?

Steph550:
Thanks for the replies.

We want to try and keep the bike original if possible, as the rest of it is completely stock. It may be worth running it with a later set of carbs to verify that it does solve the problem, but that just means buying an extra set of carbs which adds to the expense!

Cheers,

Steph.

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