Hi all,

Im new to this but been wrestling with a problem since i got my bike on the road a couple of months ago.

I bought it to do up after it had been off the road for around a year since a low speed slide. Since iv ridden it there's always been an issue when trying to go over 85mph and also when sitting at between 70-80mph in the top two gears. It feels like there is a lack of fuel getting to the engine but only at these speeds.

The bike runs fine up to this speeds and there's no issue with getting it to the red line in the lower gears. I originally thought it was the vacuum hose so replaced that, then cleaned the carbs and finally tonight took the clocks apart to see if it may have been the restrictor but all these do not seem to be the issue.

Any suggestions what else may make this phenomenon?

is the air box standard?

I had a problem with my NC30 at higher speeds because the airbox tray had been modded prior to me owning the bike to allow more air into the air box which caused a sort of ram air at higher speeds leaning up the mixture so would hit a wall like it was a massiv flat sport and slowly revv abit more.

Kennon

+1

It's usually caused by running lean due to fitting aftermarket air filters or airbox mods.

Check that you have a standard (unchopped) airbox and standard Honda paper air filter fitted (Honda part number should be moulded into it).

When you're up that high and you're topped out, if you back off the throttle slightly, does the bike then start to accelerate?

Hi all I'm a new vfr 400 nc30 owner and are having problems with the bike, it's running on all cylinders and has had the carbs cleaned etc by my local garage, the bike has a 47bhp restrictor kit on it and runs fine in the lowers gears also, its the top two gears that seems to be the issue, as funny as it sounds it happens on open roads when a gust of wind hits the bike it makes a funny sound and seems to big down and not rev any further but I know in lower gears it revs up to 13k the airbox is standard but the bike has a tyga maggot can on, thanks Oli.

is it jetted accordingly to the can but i'm thinking witht eh restrictors in place it'll be super rich would be best to test by checking the plugs and possibily returning to a standard silencer.

Kennon

Oli400nc30:

Just curious, would not 85mph be a realistic maximum speed for a restricted bike, even when jetted appropriately for a non OEM end can? No experiemce with restricted bikes myself but there must be some effect otherwise what is the point of the restriction.

peebherault:

You might want to check the fuel flow from the tank, including the tank breather.

magg, when my NC30 was restricted it'd still reach 105mph sometimes 110mph, and that was restricted to 33bhp not 47bhp

magg wrote:Oli400nc30:

Just curious, would not 85mph be a realistic maximum speed for a restricted bike, even when jetted appropriately for a non OEM end can? No experiemce with restricted bikes myself but there must be some effect otherwise what is the point of the restriction.

peebherault:

You might want to check the fuel flow from the tank, including the tank breather.

Mine makes 45hp on the dyno and it does 120mph easily.

Begs the question, what is the purpose of the restriction?