So I've just reached the pinnacle of what I thought was my NC30 build, it being finished! Everything is fine on it except when I pin the throttle and get to around 120/125mph it seems to stutter or drop cylinders or something severely restricting the pull of the engine at this speed. I can be in 5th gear pinning it and get it to near red line and it coughs as if theres not enough fuel then as I let of the throttle it picks right up again and can go again. It's annoying me because I haven't actually been able to fully top my bike out speed wise because of this issue.

All done on a private road...

Cheers in advance!

what jet sizes is it running and for which engine mods... for example race pipe? Is tank breather pipe blocked or kinked? What state of tune generally are the carbs in - clean, float heights needle etc? Air filter and intake clear?

You could try running it on reserve - sometimes helps fuel flow

Bike should rev out fine if everything is set up properly

118 fronts, 120 rears pipe werx race can (not a silly gp can, actually has a lot of dampening). Tank breather is clear and clean, routed for best flow I could get. Carbs are all good just had out for a quick clean and balance (could have done a thorough job but they already in good nick). Air filter standard and clean/new. Didn't try it on reserve but will do once Ive got another 15 amp fuse!

Got all the standard air box bits and flaps etc? Removing them can cause it to lean out at higher speeds / throttle openings (though I experienced this at more the 70mph mark)

Icemaestro wrote:Got all the standard air box bits and flaps etc? Removing them can cause it to lean out at higher speeds / throttle openings (though I experienced this at more the 70mph mark)

The front rubber flappy thing that sat underneath the airbox on the frame isn't there as I couldn't for the life of me remember how it went on. How could that effect the bike that much? I can try putting it back on but I can't remember haha.

your vaccum pipe new / ok?

ive had this many times when at speed, the older vaccum pipes can actually collapse in on themselves with the high vaccum and cut the fuel off (if you are using a stock vaccum tap)

Neosophist wrote:your vaccum pipe new / ok?

ive had this many times when at speed, the older vaccum pipes can actually collapse in on themselves with the high vaccum and cut the fuel off (if you are using a stock vaccum tap)

I replaced this literally days ago with a very high strength pipe with jubilee clamps either end to secure it thoroughly.

J-spec? De-restricted? How?

Ciao,

I have a speedo converter which i now put on the bike but yet to find an opportunity to pin the throttle on my private ride...so will have to see if it is the restriction...dont know what the restriction would feel like at 113mph...if its a judder/stutter and kicks back on instantly after releasing the throttle then that sounds like it

The restrictor drops 2 cylinders at that speed so could be what your describing