VFR 400 hiccup

[gatch]

89' nc30. Bike has done 20.5k, although I am starting to doubt this is genuine.

Ok, have noticed that the bike has started to hiccup when I go from partial throttle to wide open, if I roll the throttle on it does not do it.

Some back ground info, aside from said hiccup, bike doesn't miss or stall at any rpm. It came with a "yamamoto racing" silencer, have owned it for about 3 months. The silencer where it connects to the pipe was leaking, so I sealed it up and no longer leaks. About a month ago, I replaced the paper filter with a higher flowing foam jobby, maybe made bike run too lean ? It takes wide open choke to get it to start on a cold morning, once its warm it runs fine. When its hot, it will idle a little higher than usual, say 1700 rpm rather than 1300.

Any ideas ? I don't have a lot of experience with fueling issues apart from blocked jets.. Given that the vif has 4 cv carbs I would like a reasonable idea of the fault before I pull it to bits..

[koba]

About a month ago, I replaced the paper filter with a higher flowing foam jobby, maybe made bike run too lean ?

Or too rich? It's easy to overdo the oil on such filters.

[gatch]

Or too rich? Its easy to overdo the oil on such filters.

Ahhaha, woops, no oil on the filter as yet. In fact the filter is a one off, made from some cushioning foam I found at work....

[koba]

Ahhaha, woops, no oil on the filter as yet. In fact the filter is a one off, made from some cushioning foam I found at work....

Try the old one if you still have it, the foam may not flow well at all. It may also dissolve in petrol mist...

[gatch]

Try the old one if you still have it, the foam may not flow well at all. It may also dissolve in petrol mist...

The old one is in pieces..

Never thought about it dissolving.. Will check it out tomorrow..

[Wannabiker]

Upholstery foam may be the problem...if it is "closed cell" type it will not allow much airflow. Air filter foam is "special" ... and them type of carbs need the correct air pressure in the airbox or they wont work as designed. It is most likely rich.

Its a pretty major job doing the carbs on that bike....ask me I know!!! (re-jetting a NC30 racebike to run on avgas)

Also make sure the vaccuum lines to the fuel tap are connected properly, and you dont have an air leak.....if you have had the tank off.

[motorbyclist]

it's running rich

put in a proper filter and get the poor bike tuned and balanced by a mechanic who knows what he's doing with that model (AJ at KTL motorcycles/motohaus is awesome and i've seen him do a carby swap in under 20minutes flat)

Ahhaha, woops, no oil on the filter as yet. In fact the filter is a one off, made from some cushioning foam I found at work....

:slap:

now, boys and girls, we will all sit down and hear the tale of how the NC30 was born......

while the cbr400 of the same year was made by honda's street division, HRC - the racing crew who had just built the hugely successful RC30 - were tasked with making the smaller replica of the RC30; the NC30.

The NC30 was costly to make, and cost as much as the cbr600 sitting next to it on the showroom floor, BUT, it has since proven itself to run in it's stock form for well over 10000km with only semi-regular care and an aftermarket rectifier. It's become an icon of reliability and is still popular on today's racing circuits.

The performance of this little beastie made it a strong contender in the race classes of the day, and HRC even provided a manual to orient the already track-ready bike into full racing trim.

The manual (or atleast my english translation of it) addresses a few things, like where to cut the front mudguard and what to do to the suspension, but the most interesting part is the airbox..... which is removed entirely (filter and all; even the trumpets are replaced, holes are drilled, the insulation is removed, an air scoop is supplied etc etc).....

This gives more top end power. Unfortunately to get this you require hours of tuning, the bottom end performance suffers and the motor is fucked by the end of the season.

For long term survival and street use, the bike has a carefully designed intake tract, airbox, air filter, and exhaust system which all work in a concerted resonance to produce the power they do.

When we go slapping big ol' pipes on them and cutting bits out of the intake at random, all that scavenging and HRC tuning goes out the window. Shit, most people don't even bother to re-jet the poor thing and let it deteriorate (people firmly believe noise=power despite all evidence to the contrary).

When we go replacing air filters that may only have needed a blow-out with an air gun with bits of couch foam, god knows what will happen - it might already be full of dust to be sucked into the motor!


Just always remember - Some japanese engineer working at honda neglected his family and children for months, maybe longer, while he worked on that air filter and airbox and another whole team of engineers neglected their children to develop that exhaust: Just think of the children!