Miss-fire under load 9000 - 12000 rpm

[chownsy]

HI all, Its me again,

MOT is due soon so thought i would get her back on the road fully running, so i got the coolant cleaner in and going to put a rad seal in to stop any leaks as the water is still disappearing slowly (new flexi- hoses fitted so know its not the hoses leaking, hose in V has been sealed so know its not that leaking).

Anyway i took her out for a ride witht he rad cleaner in as it said 30 min ride needed and the misfire that i thought had been fixed was still there

It seems that under load between 9000-12000 rpm the bike just hesitates (like out of fuel even). I have set float heights, set pilot screws, balanced carbs, new rubber between carb and block, proper hose clamps. no leaks detected with brake cleaner, fuel tap fully works, tank full of fuel.

Could this be the coils and HT leads deteriating? (spark plugs are new)

I was thinking of fitting a set of dynotek 30000v coils to the bike if the coils are at fault.

Hope someone can shed some more light on this as I seriously am out of ideas of what the cause is of these issues.

Regards

Richard

(ps, i was out raced by a VW TDI transporter van and the bike wouldnt make it over 100 on a private strip, it just hit 95 and stopped going any faster)

[philfingers]

I would have tried plugs, but as you've changed them whilst it's possible to be a dodgy plug i'd start by swpping bits from a known running bike. post you're location. Someone local maybe able to help you out. I'd start by swapping coils and HT leads

[chownsy]

I live 5 miles out side redditch B49 5LH

[hunter]

I would be wanting to know were the water is going,
Are you loosing a lot of water or just a small amount,
have you replaced the rad cap,
if so and you are still loosing water it could be a head gasket,
and that could also account for your misfire.

[chownsy]

Just a very small ammount, like 100ml or something like that. Never below 1 inch in the rad when cool.

No blue smoke from engine, no water in oil, no oil in water, no excessive water vapour from exhaust and not over pressuring so know its not head gasket gone.

Rad cap has not been replaced, but thats not the issue as im wanting to fix the missfire under load. Its only under accelleration between 9-12000 rpm.

[philfingers]

does it start and run ok from cold? If it does then i doubt it's water (ie headgasket) causing the missfire. If it was then it would missfire when cold I suspect.
I have a collant pressure tester, but if it works on small caps like the VFR i have no idea.
If you wish you're welcome to bring it around to me and we can fit my coils etc, that might be easier.
I'm between Bromsgrove and Kidderminster

[philfingers]

sorry, is it NC24 you have, my bikes a '30

[chownsy]

mines a NC24 frame with NC21 engine, loom and coils.

[philfingers]

ah right, i probably won't be of much help then. I'll take a look at my Sykes coolant pressure tester and see if it will fit for you,
Phil

[isca1987]

I have the same issue with my nc35 & can not work out why. But when my bike is cold it's ok but when it is warm I have the same issue as you, also when it's happening if I change gear it stops but when I hammer it, it comes back again is this the same for you?