Stumble/misfire at part throttle

[jetblack]

Got the bike back on the road after sorting the forks and the charging system, took it for a bit of a shakedown and noticed that it is missing/stubmling ever so slightly- its not massively jerky- you can just hear its not quite right- at about 4500-6000 rpm. its fine when you open her up- pulls well all the way to the redline.

Any ideas what could be causing this?

[jetblack]

Anyone? Would be great to have something to go on?

[CMSMJ1]

What is your setup? carbs? airbox? flaps and so on?

[jetblack]

Stock nc30 Carbs. Have been cleaned, balanced (on the bench using the drill bit method), slides drilled to 2.5mm, extra 0.5mm washer under needles and rejetted to 118/120, Blueflame end can. Stock airbox, flap is in place. New plugs, new battery, new generator coils, R6 Reg rec, new oil, filer and coolant.

Bike has done 16,000 miles.

[CMSMJ1]

try without washers I reckon. Easy to do and it is in that zone. Not all bikes like that mod

[jetblack]

Im booked into a dyno on tuesday so hopefully this will help identify whats going on. I guess the washers would show as running rich in the midrange if theyre causing the problem?

[CMSMJ1]

yes - too rich at part throttle in the midrange - get a good graph on here!

[jetblack]

Will do.

took it out tonight and did about 15 miles. Its definatley not quite right at 4.5-6k but still pulls really well everywhere else. Going to give it its first long ride tomorrow- 54 miles to and from work. fingers crossed it doesn't break down!

[jetblack]

Well, she made it to work ok. Whoop whoop!

[jetblack]

Well, have had the bike on a dyno this morning at SPR racing in Ruddington, Nottingham. They were great, very friendly, helpful and knowlegeable and fairly priced (£20+vat) for a dyno run.


Its running a little rich everywhere so have been advised to drop the jets 1 size all round and put a clean air filter in (mines not propper dirty but probably due a change!)

The stumble at part throttle seems to a charachteristic of the bike not liking low revs and be me being over sensitive- looking for problems! Have covered a good few miles in the last few days and its been fine.

The operator reckons its making healthy power and pulls nicely, figures a touch low but he reckons its not far off and given todays heat, humidity and my tired chain and sprocket would probably expect to see another 3 or so extra hp on the figure.

Graphs below:





Any thoughts?