Hi everybody on the forum.
I am sending you this message concerning my VRF400 NC24, which starts easily, that runs great up to 5000 RPM and then it starts to run less regularly (up to 8000 RPM), in fact if I need to overtake, I need to leave 2 gears (from 4 to 2 for example) and then the engine runs perfectly as soon as the frontier of 8000 rmp is reached.
The sparks are new, oil and filter new, tank has been cleaned and has some cream (RESTOM kit for old tanks) , the fuel is perfectly reaching the carbs, the carbs have been cleaned with an ultrasonic engine (perhaps I could do better on this side). the battery is new.
I have made a test without the air filter (no improvement).
If somebody has had the same problem and has some clues, I do thank you

Please, forgive me because my english is not perfect, I spent some years in England but that was ages ago...
I hope that everyone is going through this covid crisis without any damage.
stay safe with you familes.

Manu from the south of France

Hi Manu,

I suspect something to do with carburation maybe an air leak or the jets & emulsion tubes are in need of a thorough clean also check the air galleries etc, my NC30 did not run right and a proper inspection of the jets along with emulsion tubes cleaned sorted it right out.

I am sure the lads in the know will have some pointers for you.

Measure the battery voltage with the engine running up to 5000 rpm. Should read no higher than 15 volts.

Thank to both of you,
I suspected something wrong with the carbs..I am working on it.
But now I see that It could have something to do with the charging system...I am a wreck on electrical stuff...I try to test the battery at 5000 rpm...and come back .( do you suspect the regulator to be dead ?) I know that this is something that needs to be carefully controlled as it is a weak spare part on the NC24..
Could it be just like RDX125 yam that needs a fully charged battery to rev high??

I was about to buy a set of carbs on ebay (from scotland) to work on the side...(in order not to make mistakes on the bike) but I missed them, damned..they were bought from a guy in ireland...by the way I was abut to buy a carbs kit on ebay (cruzinimage), has somebody already worked on his carbs with such a kit ? I have heard so many things about that sellers (which sells from Japan? which does not mean that it is manufactured in japan...

thanks to the forum for your help
Wish you a very good day
regards
Manu (sorry for my english)