Hi all,

Brand new to this forum, although I have read tons of threads since buying an NC21 KM in Thailand (which has been an incredible source of useful info, thanks guys!)! Needless to say, parts for this motorcycle are hard to come by here and the interweb seems to be the only place to find specific parts.

Anyway, I recently took the carbs out, cleaned em, adjusted the float heights, pilot screws (which were all waaaay off), but then I noticed that all my main jets are .98s. Now from what I know these should be 112s in the front and 110s in the rear. I think that the KM model was produced a couple years after the production of the last set NC21s, and so that makes me wonder whether the carbs (kei hin manufactured) may be differently set up, or whether the previous owner just slapped on 98 jets all round.

So if I do need to swap out the jets, where is the best place to find them online? And what type of jets am I looking for (thread diameter, length, height, part number)?

The help would be much appreciated as this is my first ever motorcycle I am working on, and I would really love to restore this vfr400 to its original, legendary performance!

Best,
Tyler

Some sets of nc21 carbs I've pulled apart in the past had keihin #98 jets in them - I now have a box full of 'em in the shed!

I have a feeling that the different model nc21's were indeed jetted differently. Is the KM the naked NC21? David Silvers has it listed as 1991 model, pics please!

I would leave yours alone unless there's an obvious jetting problem (e.g. so lean that it won't rev to redline).

Yes, it is the naked version with raised handlebars. I believe these were made as training motorcycles.

The bike revs fine and the jets are good, but I just don't want to lose out on performance. One thing however is a poor throttle response problem from idle: If I gas it hard from idle the engine is slow to respond, but once above 3000rpm response is quick. I'm gonna follow up on your jetting guide (great piece btw), and see where that gets me.

Thanks for the prompt response, Cammo!
Appreciated!

TeaMonkey wrote:Yes, it is the naked version with raised handlebars. I believe these were made as training motorcycles.

The bike revs fine and the jets are good, but I just don't want to lose out on performance. One thing however is a poor throttle response problem from idle: If I gas it hard from idle the engine is slow to respond, but once above 3000rpm response is quick. I'm gonna follow up on your jetting guide (great piece btw), and see where that gets me.

Thanks for the prompt response, Cammo!
Appreciated!

Your symptoms point to the jetting being goood


0-3000 is nothing to do with main jets.. its to do with slow jets, float height, pilot screw and slid spring / air hole.

if its running good dont mess with it.. ill double check the NC21K (M) parts book when im next at the bike shop, but if cammo has seen 98s before then probably ok..

Original 1986 N21 has 110/112s, The K model training school bikes are different in a few ways..

Thanks for the input, Neo. The bike is a little rough sometimes, and I actually have yet to give the slides and diaphragms a good look, so I think I'l do that just to be sure everythings in working order. Rear suspension seems to be leaking a bit too, so thats going to be an expensive fix if not replacement

Anyway thanks gentleman for the advice.

The joy and hardships continue....