SOHC.co.uk Forums > CB750
CB750K0 Carburettor Problems
mick:
are there any forum members in your area that could lend you a set of "known good carbs" for you to try ?, rather than buying some,
I doubt anyone will have a spare set of the KO carbs so you would probably have to try some newer carbs and you may have to change the throttle cables to ?,
I know it a hassle but it may help you sorting out your running issues ;) cheers Mick.
tarmac:
damn!!,..I thought a change of plug caps would have solved your problems,but i hold my hands up and admit I got it wrong.
it looks like it's back to the drawing board then???
tarmac
MarkCR750:
Sounds very similar to a problem I had with my zxr 400, in fact the symptoms are identical, it was float heights, when the engine was cold it would run fine, after riding for 5 minutes or so it would have the symptoms you describe, the only thing that was changing in that time was engine temperature, this lead me to think that it was over fuelling (running rich) , so by trial and error I adjusted the float heights, I couldn't just set the floats to the factory settings because the intake, carbs and exhaust were modified so the standard settings weren't necessarily the correct settings, at the 5th attempt the bike ran perfectly, so I guess the question is after you balanced the carbs and it ran well for 10 mins did you subsequently let the bike cool to stone cold ?, and did it run ok for 10 mins after that subsequent cold start up?, I'm absolutely sure it won't be carb balance btw, cheers Mark.
Another thought would be a vacuum forming in the fuel tank due to a blocked breather, not so likely but easy to check, just go for a ride with the fuel cap off (well life is no fun without a little danger is it!), this happened on my XJR1300 a few weeks ago, after a few miles of imitating John McGuiness the engine started to cut out, I opened the fuel cap and there was a huge rush of air into the tank, I got home by keeping the revs below 3k and found that the breather hole in the cap was blocked, no problems since cleaning it out, I doubt your bike has this problem but it's a quick check.
K2-K6:
At least you've now taken that particular area of concern out of the way, you'd have got more frustrated if you did a load of work in another area only to find something simple like defective plug caps!
They are such nice bikes to ride so hopefully with you and us lot on here we should be able to get it.
Another question, if you warm it up by riding and then turn it off and let it sit for perhaps 15mins without turning the fuel tap off.....then start and ride it, will it accelerate normally at that point or is the fault apparent immediately? i.e.will it give you one good acceleration run and then the fault returns? or does it just display the fault straight off?
MarkCR750:
--- Quote from: MarkCR750 on April 09, 2014, 02:22:44 PM ---Sounds very similar to a problem I had with my zxr 400, in fact the symptoms are identical, it was float heights, when the engine was cold it would run fine, after riding for 5 minutes or so it would have the symptoms you describe, the only thing that was changing in that time was engine temperature, this lead me to think that it was over fuelling (running rich) , so by trial and error I adjusted the float heights, I couldn't just set the floats to the factory settings because the intake, carbs and exhaust were modified so the standard settings weren't necessarily the correct settings, at the 5th attempt the bike ran perfectly, so I guess the question is after you balanced the carbs and it ran well for 10 mins did you subsequently let the bike cool to stone cold ?, and did it run ok for 10 mins after that subsequent cold start up?, I'm absolutely sure it won't be carb balance btw, cheers Mark.
Another thought would be a vacuum forming in the fuel tank due to a blocked breather, not so likely but easy to check, just go for a ride with the fuel cap off (well life is no fun without a little danger is it!), this happened on my XJR1300 a few weeks ago, after a few miles of imitating John McGuiness the engine started to cut out, I opened the fuel cap and there was a huge rush of air into the tank, I got home by keeping the revs below 3k and found that the breather hole in the cap was blocked, no problems since cleaning it out, I doubt your bike has this problem but it's a quick check.
--- End quote ---
PS I'm sure your right to suspect that carburation is the problem, it doesn't sound at all like an electrical fault.
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