Hi Folks

Can anyone help me out source the rubber flap that fits under/in front of the airbox on an NC35? A template would help if you have a flap sitting around so that I could make one.

My bike is having issues (its a track bike)....it flies to the redline in 1st/2nd/3rd, then in 4th/5th/6th gets more reluctant and won't rev out, from about 10k on. OK I'm a porker at 13 1/2 stone but at the moment shes geared 15/42 so should rev out in 6th! Its like a little misfire, or slight fuel starvation and hesitancy on a wide open throttle. My best guess is turbulent air going into the airbox, perhaps too lean at higher speeds.

Just been dyno'd, healthy 63.5hp at the wheel, good curves. Had to be rejetted to 116 all round as was rich, and runs a K&N filter in the original airbox but no snorkel or rubber flap. I'm new to the bike (and 400s generally) and done 3 track days on her so far and its a tad frustrating....if I can get her to rev to 12-13k in 5th and 6th she'll be sweet.

I'm thinking a good starting point is to fit the snorkel (I have one on the way) and the flap (which I need ASAP....HELP!). I've read what I can on this forum, which I must say is all excellent stuff, and conclude that standard spec is where I need to start from.

Have fitted new plugs, HT leads and the old coils show correct resistance.

Am I missing anything? She also has HRC carb springs and the extra 0.5mm washers fitted. Could the gearing be masking the fact that the problem also exists in gears 1/2/3?

Sorry I know theres plenty of info on here about this, really just need the rubber flap so I can self help to start with.

Cheers, Guy

I feel your pain (and guessing that you inherited it!).

Sounds pretty typical of a buggered airbox - the gearing isn't masking it, it's more down to the speed you're travelling at. Once you have the flap and snorkel you should be sweet and have a good base setting to go from.

As for the dimensions of the flap, you probably could make one, but I'm sure you could pick one up for a few quid in the for sale/wanted section - they have clamp thingies attached to them that fasten to the cross bar of the frame. Stick a wanted ad in there.

guy971 wrote:Could the gearing be masking the fact that the problem also exists in gears 1/2/3?

It's caused by the air velocity, it won't rev out in the higher gears because too much air is being forced down its throat and the bike is running lean. It won't be running as lean in teh lower gears due to reduced air/bike speed.

Fitting the snorkel and rubber flap is a good start like you say, fitting a standard filter in will also help (will probably need to jet down slightly).

RB Imports in Sydney can source most parts: http://www.rbimports.com.au/

DataRacer wrote:RB Imports in Sydney can source most parts: http://www.rbimports.com.au/

Australia?

superlite wrote:

DataRacer wrote:RB Imports in Sydney can source most parts: http://www.rbimports.com.au/

Australia?

Yes. Sydney is in Australia.


Oops! Thought the OP was in Oz...!

guy971 wrote: Just been dyno'd, healthy 63.5hp at the wheel, good curves. Had to be rejetted to 116 all round as was rich

Did you ever ride it with the 'rich' jetting??

DataRacer wrote:

guy971 wrote: Just been dyno'd, healthy 63.5hp at the wheel, good curves. Had to be rejetted to 116 all round as was rich

Did you ever ride it with the 'rich' jetting??

Yes, round Brands Indy in the wet (first time I rode the bike)...wasn't sure at the time if it was the damp causing a misfire or the fuelling. After that, had it Dyno'd and jetted down a bit and the filter changed from a modded thin foam one to a K&N which we had spare, next time out in the dry, same track, same problem

Maybe too many changes at once! The bikes a good one though and I'm looking forward to ironing this problem out even if its at the expense of a bit of power. My other half has a fairly standard NC30 which has almost no vices, not as powerful though, but very nice to ride. Hopefully, when (& if) I get good at riding a 400 I'll be back asking questions about getting more power!

Now have a rubber flap on the way too, so will report back on progress when its fitted with a snorkel. Thanks for your replies folks.

Cheers, Guy

Have you got a copy of the fuelling mixture graph from the dyno ?

guy971 wrote: Maybe too many changes at once!

Possibly. With a standard filter you would probably run around 115 main jets.

It would be a wise move to go back to use a standard filter once you have the snorkel and flap in place, all that aftermarket filters do is make it hard to guess what jets to use!

Does anyone have a picture of how the rubber flap fits that is associated with the airbox? I'm normally quite good at working this sort of thing out but this has beaten me!

Do the carbs need to come off to fit it?



Heres a picture of the flap I now have, anyone know if its the right one for an NC35?

What is its purpose in life?

Thanks in advance....

Cheers, Guy