14-08-13, 07:17 PM
Well, I hope it won't turn out to be that!
So, the symptoms have been that approximately between 3-4k rpm, if I came off throttle very slightly, for instance when regulating throttle to match traffic speed, the bike gets a jerky stutter. It did it at exactly the same revs in every gear. As soon as I got clear of that rev band, it cleared so that above those revs it pulled cleanly and strongly just as it should. Below 3k it's a little glitchy, but no more so than I expect on these bikes (it hasn't been Ivanised yet). I have covered a little over 3000 miles in 2 months with these symptoms, and during that mileage the problem hadn't altered at all in any way. It doesn't do it if I accelerate through that rev band, only coming off throttle. And if I come off throttle slightly anywhere else in the rev range, it doesn't do it. If I come completely off throttle at any revs, the revs drop normally, there is no sticking that would suggest an air leak of noticeable proportion.
Today I had it looked at by a mechanic who was recommended to me. He cleaned the carbs, and noted that they were perfectly set up. Then I test rode it. It then only showed the symptoms at just about bang on 3k, instead of through a band of about 1000 revs. Still only when coming slightly off throttle, but every bit as bad at that point. He changed the plugs. I test rode it again, absolutely no further change. The old plugs came out a perfect light brown colour on all 4. (I've kept them as spares).
There was no time to investigate further today, but he said his next moves would be:
Ultrasonically clean carbs.
Check O rings at carb rubber-to-cylinder head face, as he said these can flatten down a bit and if even one was letting in just a little air it could cause the symptoms I'm experiencing.
We were both in agreement that it is not likely to be an electrical fault as a) it hasn't worsened with further use. b) it would likely be worse at higher revs if it was something electrical breaking down, ie, under heavier load. c) cleaning the carbs has improved things, although not eradicating the problem entirely. d) changing the plugs has made no difference. HT leads and plug caps are all in excellent condition.
There is some cracking in the carb rubbers, but it does not appear to have gone all the way through. The air filter appears to be in new condition.
We have decided for now that as Mike will be Ivanising it in September anyway (I hope - unless he disagrees), it might be an idea to see if this makes any difference to the problem.
Thoughts anyone?
So, the symptoms have been that approximately between 3-4k rpm, if I came off throttle very slightly, for instance when regulating throttle to match traffic speed, the bike gets a jerky stutter. It did it at exactly the same revs in every gear. As soon as I got clear of that rev band, it cleared so that above those revs it pulled cleanly and strongly just as it should. Below 3k it's a little glitchy, but no more so than I expect on these bikes (it hasn't been Ivanised yet). I have covered a little over 3000 miles in 2 months with these symptoms, and during that mileage the problem hadn't altered at all in any way. It doesn't do it if I accelerate through that rev band, only coming off throttle. And if I come off throttle slightly anywhere else in the rev range, it doesn't do it. If I come completely off throttle at any revs, the revs drop normally, there is no sticking that would suggest an air leak of noticeable proportion.
Today I had it looked at by a mechanic who was recommended to me. He cleaned the carbs, and noted that they were perfectly set up. Then I test rode it. It then only showed the symptoms at just about bang on 3k, instead of through a band of about 1000 revs. Still only when coming slightly off throttle, but every bit as bad at that point. He changed the plugs. I test rode it again, absolutely no further change. The old plugs came out a perfect light brown colour on all 4. (I've kept them as spares).
There was no time to investigate further today, but he said his next moves would be:
Ultrasonically clean carbs.
Check O rings at carb rubber-to-cylinder head face, as he said these can flatten down a bit and if even one was letting in just a little air it could cause the symptoms I'm experiencing.
We were both in agreement that it is not likely to be an electrical fault as a) it hasn't worsened with further use. b) it would likely be worse at higher revs if it was something electrical breaking down, ie, under heavier load. c) cleaning the carbs has improved things, although not eradicating the problem entirely. d) changing the plugs has made no difference. HT leads and plug caps are all in excellent condition.
There is some cracking in the carb rubbers, but it does not appear to have gone all the way through. The air filter appears to be in new condition.
We have decided for now that as Mike will be Ivanising it in September anyway (I hope - unless he disagrees), it might be an idea to see if this makes any difference to the problem.
Thoughts anyone?