Nc30 race bike starting problems

[col4555]

Hi,this is my first post and I hope you can make sense of it.I have recently purchased a vfr400 nc30 recebike.First sign of trouble was when ticking over it started to backfire when warm.I had this inspected by a mechanic and jetting was 112 all round.Jets now changed to 120,125 (shotgun cans).The bike started ok for a week then the plugs decided to die.Plugs changed but bike takes around six attempts to start,the first few attempts it doesn't sound like there is any fuel then it starts spluttering into life.Once warm it runs perfect.The bike is running total loss,the battery is fully charged when attempting to start the bike,and also the choke works but doesn't seem to make starting the bike any easier.Any help appreciated thanks Colin.

[magg]

Poor fuel flow from tank. Vacuum hose ok, vacuum tap ok?

[col4555]

Hi,yes all checked and ok.The tap doesn't turn off but I don't think its causing any probs.

[magg]

Usually need choke for first cold started, particularly after a week or so standing. Once started does choke should increase engine revs without using the throttle. Why does fuel flow with tap off, even HRC modified taps turn off. How much flow do you have.

[col4555]

The bike has only to be left overnight after a full day at the track and then won't start properly the next morning.The tap just passes when in the off position not much just dribbles .sorry for the confusion.

[magg]

For my road bike I use full choke after overnight but it fires up after a few seconds cranking and runs hard until I back the choke off. If you are not getting similar results I would suspect the choke function. I must confess I have done the HRC mod to eliminate the vacuum function as I have had difficulty with starting after a week or more without use. Suspect fuel evaporation was leaving carby bowls low and fuel tap vacuum at cranking was insufficient to fully open the tap to fill the carbies before battery went flat.

Also rereading your initial post, a main jet change would not have improved the idle, onl the top end running. Maybe he made other changes, any ideas what he did besides changing main jets.

[col4555]

Choke is definitely working.When I've eventually got the bike up and running I've pulled the choke on and the revs rise straight away.All the mechanic did was the jets.When I purchased the bike the bike the seller claimed it had rvf400 carbs and rvf hrc cdi.When taken apart it was found to have vfr nc30 carbs and a rvf hrc cdi.My mechanical knowledge isn't the best and I don't know if the cdii being different would cause any problem.

[magg]

RVF and VFR ignitions are not interchangeable, but either way would not affect starting. What makes you thick it is an HRC ignition. Just to clarify, you use full choke ON to start and then after the engine is running the choke is backed off.

[col4555]

I can't be certain it is an rvf cdi,somebody has just written on the top of it (rvf hrc cdi) so it probably isn't if that's the case.I have owned a few of these in the past so I'm quite familiar with the starting procedure,I will have to dig a bit deeper and hopefully it's something daft.

[Neosophist]

cant remmeber off hand, too late here but did hrc even make an f3 kit cdi for the rvf?

could be a chiense kncok off.

since its running total loss, battery is fully charged right? shit battery will often crank engine but make it hard to start.. using a good dummy will let you test that.

is airbox still there? all standard?

asked the old owner how they started it?

without seeing it there could be an awful lot of false herrings.

since you have some familiarity with the bike can skip a lot of the basics but id make sure there are no vaccumn leakes / carbs are jetted properly, pilot screws ok, balanced etc.

are the valve clearances ok? excessivly tight or loose valves could make it hard to start.

compression ok? a thrased race bike might be well worn out.

if your suspecting fuel then a dummy tank (pop bottle etc) and a dummy hose (long pipe) directly into the carbs might help.

carbs float valves could be leaking, draining the fuel overnight and it needing some cranking to get fuel to the engine to start.. which could be draining your weak total loss battery causing hard starting for example.

if you set up a pipe directly into the cabrs.. dont neeed to be long and stick a funnel in it.. brim it until you can see fuel in the funnel and wait an hour.. see if the fuel level drops by itself indicating leaking float valves.

gonna have to make a big list of everythign that can cause your issues and go thru 1 by 1.

fuel - carbs / carb settings / balance / choke / fuel tank / hose / tap
air - vaccum leaks? clogged filter / box / valve clearnces.
spark - electrical system / kill switch / battery

good luck