My VFR had not been started for about 4 weeks so I knew it would take a bit of cranking to get her started. Tried that but no start. Left her for a couple of hours and tried again, she tried to start but clearly all was not well.
Checked spark, a good one there, so decided it might be fuel.
Removed the tanking hoping the vacuum tube might have come off, no such luck.
Removed the fuel tap thinking maybe the diaphragm may have failed, no, all well there.
For a few years now I have not been able to select "reserve", the "knob" would not turn to that position, also getting difficult to switch from off to on. So I took the opportunity to investigate, I can see something has broken inside the tap. Replaced the tap with another (acquired when the reserve position became unavailable). Reassembled (with the vacuum bits from the failed tap) and she started up and has continued to do so.
Without dismantling the tap I cannot be sure to my satisfaction that I have cured the problem.
Anyone else had this happen.
John

Yep I've had the fuel tap break before - bit of the internal that helps select the fuel flow direction snapped inside. No idea how.


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Looks like I may have spoken too soon. Tried to start her this morning, no go, tried again a couple of hours later and started easily. Seems like the fuel struggles to get to the carbs. I took the tank off and put a length of clear tube on the fuel pipe, filled it with petrol, started the bike, the fuel drained into the carbs and ran well. I'm hoping this suggest the carbs are OK. Going to borrow a hand vacuum pump to see if the tap functions properly.
Anyone with any ideas as to what else may be wrong?
John

Suck on the vacuum tube and fuel should flow freely. Alternative is to convert tap to non vacuum, no need to crank engine to get fuel flow.

Tried that and a few other things on the fuel side, all seems OK. I have noticed the spark seemed to become erratic while trying to get the bike to start, now there is no spark at all. Looking like ignition rather than fuel. Tried new spark plugs, no different, checked the coils, they seem OK. Done all this with a fully charged battery. Beginning to think there may be some serious failure on the ignition side, any thoughts?

Check +12 volts is available at the ignition unit. Apply smell test to ignition control unit, can be a useful way to check for over voltage damage and/or remove ignition control unit PCB from case and check for damage.

Would that be the unit that sits above the back lights?

Under the tail lights, yes.

Thanks, will have a look.

I've now been trying to get the bike to run for the last couple of weeks. Sometimes she starts, sometimes not due to no spark. I have worked through all the ignition components and checked them as detailed in the workshop manual, the only thing I cannot do is measure the peak voltage, I don't have the device to do this. Everything else checks out OK.

So I thought there must be a bad connection somewhere, continuity is good as are the voltage readings at various points. That would also suggest that the earths are good.

When the bike runs I have wriggling the connectors and tugging on the wiring loom trying to find a bad connection, no signs of one.

I've opened up the ignition unit as suggested, no visual signs of a problem there and good continuity back to the various things connected to it.

It has what I think is a HRC de-restrictor wired to it, no idea how to check that. I am going to remove it from the ignition circuit and see if the spark returns.

The intermittent nature of the problem suggests that the electronics are OK, they either work or they don't, usually.

Anything else I can try, I'm running out of ideas!

John