NC24 troubles.. Engine cutting out?

[TTR]

Hi there

Just recently had the collector box swapped out on my NC24, and had a new link pipe made up, aswell as having cleaned the carbs and had the valve clearances done.

Anyway, just picked it up from the fab shop doing the link pipe the other day, and it seemed like she was running on three, so we figured probably a fouled plug or similar and to check it out when I get back. So off I go, and a mile down the road (on the m271), the engine just suddenly cuts out, revs smoothly drop and I'm pulling over onto the hard shoulder. The electrics are all working fine, lights etc.. So I try to start her up again, hit the starter a good 600 times, but nothing - the starter turns the engine over but she wont fire.

Fast forward a day, and a night of charging the battery up after my battle with the starter, and I have the bike in my garage (breakdown recovery for the win), and on the offchance, on my way to the bus stop I decide to try starting her up. And after a few tries, yep, you guessed it, she fires absolutely fine. So I dive back in the house to get my gloves, and have a mosey at the header pipes - seems she's firing on all four now! Very strange.

Fast forward another day, and I now have time to have a look-see. So on advise from the chap who did my collector & valves, I decide to check the fuel tap first. Now the plot thickens! My fuel tap has three settings - on, reserve and OFF? Odd for a vacuum tap?

So I'm musing over which to set it to, in order to remove the tank. I decide to try off, out of curiosity. So off comes the vacuum pipe and I go for the fuel pipe - next I know fuel is trickling out down my arm, quickly stick the pipe back on and go for on this time - off comes the fuel pipe and it starts PISSING OUT all over the place?!

Correct me if I'm wrong but nothing should happen when set to on, surely, if it's a vacuum tap?!

Seriously confused about what's going on with this bike! Any thoughts appreciated!

C&KR

T

[TTR]

Ah double post

Just found the link to the NC24 manual on here - seems it should be on/off/res, fair enough - though that's confusing in and of itself.. Is the 24 not vacuum fed?

Fair enough though, so that's probably not the culprit after all, which leaves me at a bit of a loss really!

[castrol101]

The 24 is vacuum fed, as is the 30 (and 35??)

However if fuel pisses out even when it is not under vacuum then there is a spring missing from the fuel tap that holds the diaphragm in place. Its quite a common mod to increase fuel flow, but it does have its negative effects. Mainly a flooded engine, and a wet arm when you remove the fuel tank

Its normal for a little bit to trickle out in the off position when this mod is applied. Just stand the tank up against a wall to stop fuel going everywhere :)

[Neosophist]

sorted it yet?

That the manual I scanned in by any chance? :) I'm 1/2 way scanning the workshop manual but its taking its time!

I know if I run the fuel out of the carbs it's a bitch to get it going again, could have just been low fuel / bad vaccumn?

[TTR]

Fair enough, but would that mod cause the engine to cut out? Or is this probably unrelated? Figured up the propping it up against a wall thing after a good soaking and wasting a few pence. Probably worth replacing the spring then aye?

And to Nesophist - not yet, no. And yes, 'tis indeed, cheers for that!

Fact that it's working now is what confuses me a bit. Also hard to find a fault that's not currently present! But then again don't really want to take her out if I'm gonna have to push her back. Or at least spend the whole time worrying about having to push her back!!

[Neosophist]

Hmm, Interesting one there.

I'd say it was probably some kind of fuelling problem.

Have you made sure the choke mechanisims are all engaging / disengaging properly as they sometimes stick open, engine could have flooded itself and sorted itself out after standing?

[castrol101]

i would replace the spring yea. But I don't see why this would cause what appears to be an intermittent fault.

Could be an electrical fault of some kind?? But i nothing of electrics so i wouldnt know lol.

Are all the HT leads connected correctly and the caps arent corroded?

[TTR]

Hmm, Interesting one there.

I'd say it was probably some kind of fuelling problem.

Have you made sure the choke mechanisims are all engaging / disengaging properly as they sometimes stick open, engine could have flooded itself and sorted itself out after standing?

Hm, see, matey who did my valves and collector box reckons it's fuelling too.

I'm not so sure, okay, fair enough you both probably know better than I, hooowever... Can't help but think if it was fuel starvation, it would have felt like running out of fuel feels - ie, choke splutter burble die... And surely if it had flooded it would have bogged down before cutting out?

I think excess fuel must be accountable for the fact that it was firing on three, but yeah...

i would replace the spring yea. But I don't see why this would cause what appears to be an intermittent fault.

Could be an electrical fault of some kind?? But i nothing of electrics so i wouldnt know lol.

Are all the HT leads connected correctly and the caps arent corroded?

It's wierd. Something tells me it's electrical, somehow. It just seemed so sudden. But for all four cylinders to go? What part would have had to die, that could come back to life overnight?

Maybe a loose connection... Pulse generator or something? It'd be before the HT leads, I would have thought, if not, indeed, before the coils? Stabs in the dark, in all honesty, though.

[castrol101]

the reason i guess at electrical is because it seems on and off, like a loose connection somewhere, mechanical problems don't tend to fix themselves and return.

And your right fuel starvation would give the splutter/die feeling.

Maybe pulse generator but as i said i don't know much bout electrical.

Another thing to look at is corroded connections in the kill switch? This could cause a sudden cut out, and it would still spin fine on the starter but not fire?? Something to check i think.

[TTR]

Well!

Had a gander at the wiring diagrams in the Haynes manual.. Admittedly for the 30/35, but it seems to be a common feature that the killswitch comes before the ICU in the circuit.. So to cut all four cylinders it would have had to be there, or at the ICU itself, assuming the problem is electric.

So I had a look at the connectors both ends.. Pretty much look fine and dandy, no problems there. So that leaves the ICU, right? But I'm thinking if the ICU failed it would stay dead, not just randomly jump back to life?

So in a moment of desparation (I really don't want it to be fuelling, carbs confuse and scare me!) I took apart the switch assembly for the killswitch and had a right good poke around inside.

I have no idea how likely it is that this would cause my problem, but the contact plates on the switch itself, and the housing, where the switch completes, or breaks, the ignition circuit, were dirty as hell - covered in grease (presumably for the little ball bearing affair on the other side? Or just 20 years of grime and crap, I don't really know!) type stuff and some weird green-ish gunk.

So naturally I cleaned them off with some wd40 and a good scrubbing.

How likely is it, do you guys reckon, that this is the root of the issue?

I'm getting mixed verdicts - Elliott up in Swindon has suggested I check the fuelling, a matey I know has suggested electrics, I lean towards electrics (wishful thinking?), and another forum has largely suggested fuelling...

It's bad, because I really want this to be it, so I can just get her back on the road, I love that bike damnit!

Anyway, that aside, thoughts?