Running rough at High Revs

[Grim]

Hi all,
Anybody experienced problems with their bike running rough at high revs?

Mine has just been serviced and since then it has been stuttering from 5tho in 3rd gear. The bike pulls we in 1&2 up to 7thou, and is fine in 3rd up to 5 thou, after this it hits a flat spot.

The bike is running Remus cans and a K&N air filter?

Any ideas?

G

[stef]

can it be carburation problems ?
did you remove the side pods (the grey triangular ugly thinggies) ?
i suspect float height, carb imbalance (in fact, very likely) or the atmospheric pressure breather pipes facing the wrong way (also more likely).

[crust]

if it was ok before the service and isnt now

sounds like fuel starvation

lift the tank and check the fuel line is not kinked or kinking as the tank is lowered

fairly common problem on m900

:) crust

[Grim]

Thanks for the advice. The bike has been back to the guy who serviced it and he was/is baffled by it. Its not the fuel hose. The ugly grey pods have not been touched, and the guy has fiddled to death with the carbs.

The dyno showed the bike was running way lean at high rev's but rich at low revs.

He has now managed to 'fix' the problem by refitting a standard airfilter, but I cannot help think this is not a true fix but simple masking the problem.

That said I'm making the most of it.

G

[stef]

Thanks for the advice. The bike has been back to the guy who serviced it and he was/is baffled by it. Its not the fuel hose. The ugly grey pods have not been touched, and the guy has fiddled to death with the carbs.

The dyno showed the bike was running way lean at high rev's but rich at low revs.

He has now managed to 'fix' the problem by refitting a standard airfilter, but I cannot help think this is not a true fix but simple masking the problem.

That said I'm making the most of it.

G

yes, that's not right (iMHO)
i would really double check the carb balancing. this used to be a problem on mine, because i was balancing then at idle. the bike would run fine up to 4th of fifth, but with speed, it would just stammer and run rough.
i then balanced the carb at idle, reved up, and refined the balanced (which was off) at higher rpms.
problem solved. now smooth all the way.

[Zimbo]

Have you just put the K&N on, and perhaps cut the top out of the airbox?
Basically it's incorrect jetting. You need to rejet the carbs and set the needle heights. A stage 2 Dynojet kit is the quickest and easiest answer. You should then be able to run the K&N and open cans with an open airox and it'll pull much better and run smoother than ever.

[Grim]

Thanks for your thoughts guys.

Bought the bike 4 yrs ago with the K&N filter, needles, cans and pretty dyno results and up until a year ago no problems. The air box had been opened.

Last year had problems at low revs (around 3K) which I initially put down to carb icing, however the problem became worse and no amount of Silkolene would fix.

Dropped the bike off to a 'specialist' as opposed to dealer, after much investigation, he found the needles were worn and he 'solved' the problems by fitting standard needles (I assumed all needles, but may be not).

Then this year problems at high rev's, hence my concern that there is an underlying problem that needs addressing.

I guess take it down a tuners and get them to set it up.

G

[stef]

yep, or give it a go.
it's not that difficult if you take your time.
but if the needles were replaced by originals, i would swap them back to stage 2 . they have to match the jets, if i rememeber correctely !