Vfr400 nc21 high speed running problems.

duanebray_08 · Post by **duanebray_08** » Thu Jun 21, 2012 8:29 am

Right, I have a nc21. It runs brilliant in 1st,2nd and third and gets to about 80mph no problem. The issue in having is as it hits around 9/10k revs it stops acceleration and just stays at the 9/10k revs. If I change up a gear it decreases to around 7/8k revs and will not go up and once this happens in either gear it's like the bike wants to go but is hesitating. The carbs have been ultra sonically cleaned, it has a brand new air filter and plugs and have tested the plugs with a tester and they all spark really well. My mate said it could be the coils breaking down at high revs so changed both coils with some old ones known to be working and still the same problem. I though the coils were a long shot as in 1,2,3 gears I can redline it. It's more like its a speed problem than a rev problem if you get what I mean. Any help would be appreciated as its plenty fast for around town but annoying on the long straights out of town. Thanks.

Post by **Neosophist** » Thu Jun 21, 2012 12:33 pm

duanebray_08 wrote:Right, I have a nc21. It runs brilliant in 1st,2nd and third and gets to about 80mph no problem. The issue in having is as it hits around 9/10k revs it stops acceleration and just stays at the 9/10k revs. If I change up a gear it decreases to around 7/8k revs and will not go up and once this happens in either gear it's like the bike wants to go but is hesitating. The carbs have been ultra sonically cleaned, it has a brand new air filter and plugs and have tested the plugs with a tester and they all spark really well. My mate said it could be the coils breaking down at high revs so changed both coils with some old ones known to be working and still the same problem. I though the coils were a long shot as in 1,2,3 gears I can redline it. It's more like its a speed problem than a rev problem if you get what I mean. Any help would be appreciated as its plenty fast for around town but annoying on the long straights out of town. Thanks.

So you'll be doing about 100mph in 6th at 10krpm.

How heavy are you? And have you head the bike dyno'd?

Is the gearing standard? [15/45]

It should do around 120mph (12k/rpm in six) so not a lot more, but if your over 10 stone you'll find it might come down a bit.

duanebray_08 · Post by **duanebray_08** » Thu Jun 21, 2012 2:01 pm

I'm 13stone. It's not like it's the power dies off. It get up there quickly but it suddenly stops pulling. I'm thinking it maybe the main jets or something to do with the carbs as the ignition side of things seems to be good. My next door neighbour has a motorbike dyno at work so will see what it's gonna cost for a run on it see if it sheds any light on the problem.

Post by **Neosophist** » Fri Jun 22, 2012 12:28 pm

Get it on the dyno see what it's doing.

It's not been restricted to 33hp has it?

duanebray_08 · Post by **duanebray_08** » Fri Jun 22, 2012 10:32 pm

No, it's not restricted. I'm gonna strip the carbs and make sure the jets are standard and the imulsipn tubes are in the right way. If then it still isn't right I will get down to my nearest dyno. I'll let you know how I get on.

Vfr400 nc21 high speed running problems.

Vfr400 nc21 high speed running problems.

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Re: Vfr400 nc21 high speed running problems.

Re: Vfr400 nc21 high speed running problems.

Re: Vfr400 nc21 high speed running problems.