Runing issues with vfr - spark (i think)

[Lilley]

Hi guys, I recently had the chance to purchase myself a vfr400, and having a minor* running issue with it.

The problem seems to be that occasionally there will be no spark. When I say occasionally, I mean completely randomly. It will be fine for 300 km, and then next time its started it will conk out 2 km later. Or in the middle of a ride it will cough and die. Restart quickly then die again 15 seconds later down the road.

I'm certain that it is not mechanical. Fuel is still being injected into cylinders when the throttle is kept open as it will backfire a bit. It's either on or off, no spluttering or lost power, just all or nothing. It's all cylinders at once. This is making me think that the spark is being impeded by something. I don't think its the coils wearing out as they should last ages and wouldn't all happen at the same moment. I think I have got it down to either a bad grounding for the spark plugs or a dodgy distributor/cap. The battery grounding is fine, as lights still work when the bike cuts out.

Can anyone confirm, or suggest other things to check, and how to check them?

As a seperate issue, the tacho overreads like a bitch, about 2.5 times higher than it should be. Occasionally it will read accurately though. The indicators are also incredibly temperamental and only work very occasionally. The bike is a ex-track rebuild job I believe and I think they may have done a pretty standard job of the wiring all round.

cheers.

[uber pikey]

This sounds like a wiring issue to me, where it must be off loading to earth from time to time. It will have to be con checked just to see where it is going to earth or two wires rubbing together.
This is just my opinion, hope someone comes along with more info.

[CMSMJ1]

Sounds like you need to get all the earths checked as you seem to have an issue there. Does it have a standard ignition and a kill switch? Is it an NC30 with all NC30 gear or has anything else been changed?

Earths for my 20p bet

[Lilley]

Does it have a standard ignition and a kill switch?

yep

Is it an NC30 with all NC30 gear or has anything else been changed?

no idea. I think most of it is fairly standard going by the looks of it.

Thanks, will have a hard look at the grounding points. Any idea where I could find some sort of circuit diagram?

[uber pikey]

Mr Haines is helpful here I'm afraid, hope you have one.
Then again if you dont just follow a simple plan and test everything methodically.

[skinnydog0_0]

I would put my 20p bet on a faulty kill switch

[Lilley]

or a faulty side stand switch?

[Cammo]

vfr's don't have a sidestand switch.

Check the earths like the others say!