i know you guys heard of this problem before...
but any help will be great. i bought my nc30 bout a year ago. it ran fine other than that stupid flat spot between 5000 and 7000rpm. i had my bike on a dyno and it hit 212km/h. it produced 53bhp. which i tought was great for a 400cc. anyways, i wanted it to run smoother buy getting rid of the flat spot. so we cleaned the carbs and replaced the diaphrams. the flat spot seemed to dissappear, but now my bike seems to be hold back power as soon as i hit 11000 rpm it bogs down like and she doesn't want to rev up lthru the gears like she use to. it can't even rev high enough in 5th gear to switch over to 6th.

it recently came to my attention that the diaphrams i had in when i bought the bike was an HRC set i believe. it has a curve and two holes on the piston. i replaced 3 inthe mean time with the stock vfr diaphrams. im sure this can't be the problem as i ran the bike after cleaning the carbs with all 4 hrc diaphrams and it still game me the problem.
help!!!!!

guys at the moment my bike is extremely slow. has anybody had a problem like this?
i need to fix it.
a stupid nissan sti drove me away last night... im depressed now

hello mate..........212kph is very fast for 53bhp!!!!!! 131mph

what exhaust system is the bike running????standard or aftermarket?

the falt spot between 5-7 grand is usually due to the exhaust system,whether its been rejetted to suit.

it most definately sounds like a fueling issue so maybe take them apart and clean them.check what size jets its running etc and make sure everything is ok.



wull

i had the exhaust on since i bought the bike. i have no idea what type of exhaust it is. it looks like the standard can but with the inner pipe removed. so im not really sure if the jets were done.

the problem began with cleaning the carbs. i should of just left the stupid thing like it was.

You need to tell us what jets are in the carbs and also are there any mods to the airbox, filter etc?

i think the jets are standard size (120mm i think).
i have a standard air filter. but my box has a crack in it. hmmm, but it still seals properly.

the bike was fine other than the flat spot @5000 and 7000rpm, before i had it cleaned and balanced....

you think they are std...but are they?

You said you removed HRC slides...if you had them int eh bike you would be looking to run HRC sized jets adn no airbox,

Do you have the rubber flap at the front of th airbox? and is the snout still on there?

yip i think so. if i had bigger jets i wouldn't have the flat spot in the first place. right?
had a standard airbox all the time. the rubber flap is still there and the snout. still stock standard... i think it's time for a new filter thou.

will keep you dudes updated.

mambraNC30 wrote:yip i think so.

Until you SEE what jets you have in the carbs it's not worth trying anything.

You'll never know how much the previous owner/s screwed around with it.

crap!!! i forgot about this post.

got my 30 back from the machanic. 204km/h in 5th gear at about 13500rpm... great!!!
120mm jets front and back. new chain and sprockets.
but i still get a slight 'bogging down' when i run in the high revvs. it's friggin annoying.
i have a brand new air filter. i think its bogs the worst in 6th gear. anybody know what the hell causes this?