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-   -   flat spot (http://www.horizonsunlimited.com/hubb/yamaha-tech/flat-spot-6402)

bigbrummer 1 Sep 2005 01:45

flat spot
I took my bike for its first long weekend away post running in. I seem to have a flat spot in the accelleration, in 4th and 5th at around 100kph. It doesn't do it every time, and tends to do it more when really pulling such as on a hill. I'm 99% certain that the clutch isn't slipping. The baffles on the exhaust are rattling, and I'm going to take them out. Could the two be connected?
Other than that 500 plus sunny trouble free miles around the south of England. Just what the doctor ordered.

FredXTZ 1 Sep 2005 02:37

BigBrummer, it seems like you have a carb setting job to do. First make sure your air flter is clean and you don't get false air in somewhere [rubbers between carb and head?]. The exhaust wil not cause problems like that. The only important thing is volume. If you have the standard can, no sweat. You can try to improve breathing out a bit with a drill or a saw.
Matt : synthetic oil is not good for our antique engines. Try mineral oil that is specifically for motorbikes. People say that car oil will do, but since you already seem to have a clutch problem, don't try.
p.s. we have the international Ténéré meeting in Holland coming weekend. Drop by and we will diagnose all your problems.

Fred, XTZ660, Holland.

Matt595 1 Sep 2005 04:07

Hi Fred,

Yes I use synthetic oil, because this way I keep it longer than mineral, 8000 kms instead of 6000 kms.
Synthetic is also appropriate in warm weather as summertime..
There is a risk of cluth slip but I only experienced this once when clutch had 80000kms and worn.
I think my "clutch slip" alike problem is solved.
I found a broken link on my chain, making chain slap excessively against swingarm.
The link was bend, probably because something as stone or other got trapped between pinion and link.
It was still useable, though, it would have ended up with chain going off again.

Thanks for the invitatation, I´ll try come service my bike and meet with the dutch tenerists one day, would be fun.



bigbrummer 2 Sep 2005 01:43

Thanks Fred
When you say carb setting, do you mean changing jets, or are there screws which will adjust the mix?
If its any help, I've now noticed that the problem seems to exist if I accellerate quickly at that speed, rather than smoothly through the revs.
Best Dave

aukeboss 2 Sep 2005 03:58

carb adjustements:
1. Idle mixture. This is not the issue here. Small screw just in front of bowl, difficult to get to. They first engineered the thing w/o starter motor and then put the starter on.
2. Jets. They only determine mixture at full throttle. Unlikely cause.
3. Float level. Unlikely cause if engine running well for the rest.
4. Needle positions. At first thought would think your problem might be solved by lifting needle second carb (right hand) one or more notches making mixture richer during acaccelaration.


bigbrummer 3 Sep 2005 01:32

Well, my 1% of uncertainty regarding the clutch proved right. My flat spot is indeed a very slight clutch slip at around 4k revs. I assume the plates are slightly worn. Will have to have a look and see.

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