Intermittant mis-fire

[Active Rascal]

Cheers Mike, that's what I'm looking for, trying to narrow it down. If it happens again, and I really do hope it won't, I will try and take note of a few things as I say and a video. It's just a bugger being intermittent in that it's hard to diagnose or swap things around and tell if you've found the cure. It certainly doesn't happen every ride.

It did mis fire a while ago whilst out, took out plug on the lane, tapped carb and ran fuel through, drained float bowl and filled, clean (but not new) plug in and WHAM..... ran a treat, revved out clean as a whistle. This was with a 9 plug, only been ridden twice with the 8 plug.

[helisupp]

It sounds to me like an electrical part is being given time to cool down whilst having a fiddle with other things.

Just try a coil, nothing to lose trying one.

[fallenmikethebike]

Cheers Mike, that's what I'm looking for, trying to narrow it down. If it happens again, and I really do hope it won't, I will try and take note of a few things as I say and a video. It's just a bugger being intermittent in that it's hard to diagnose or swap things around and tell if you've found the cure. It certainly doesn't happen every ride.

It did mis fire a while ago whilst out, took out plug on the lane, tapped carb and ran fuel through, drained float bowl and filled, clean (but not new) plug in and WHAM..... ran a treat, revved out clean as a whistle. This was with a 9 plug, only been ridden twice with the 8 plug.

And it's been fine since then? It might have been a some foreign matter in the float bowl obstructing the main jet?
Mike

[Active Rascal]

No, it's still been intermittant since. The last time green laning had a brand new B8EGV in.... Ran perfect first thing... Then fouled quite bad for an hour or so then ran really really well. Has been out once since for a couple of hours... Again ran fine. I'm supposed to be out this weekend so will soo then how it goes.

[Active Rascal]

In addition..... When mis-firing the tick over is also very weak.. And usually cuts out at gates. When running right it will tick over sweet as a nut. Maybe a weak spark?? This is why I don't think it's dirt in the fuel. The fuel used had been in a jerry can for a good 3 weeks or so but wouldn't have thought this would matter. Coincidentially ran fine after filling up with fresh fuel. Im not saying directly afterwards though. It's always been ran on super unleaded due to the engine mods.

[helisupp]

Regarding super unleaded, I am not sure a 2 stroke ever needs it, no matter what the state of tune.

Comments.........

[Active Rascal]

Think I read it on here, have never tried it without, apart from the odd time it's been mixed with normal fuel when that's all the station has.

So I read with higher compression you should run higher octane fuel to avoid pre-igniting..... something I don't know an awful lot about so just go with the super unleaded, think Steve on here advised me to also a while back.

[knackeredMk1]

The only reason for using super unleaded is that Shaun is using a Mugen cylinder head that increases the compression ratio to the extent that the engine needs to run on a higher octane fuel for engine longevity.

[Active Rascal]

Well, went out green laning all day yesterday, did probably about 120 miles in total.... and she ran fine all day. There was the odd very very slight bogging in the morning, but it was extremely damp, foggy and quite cold. Temperatures about 4/5 degrees first thing with heavy fog/mist which then lifted as temperatures increased to about 10/11 degrees. Tickover was fine, and the bike revved out clean as a whistle all day no problems.

I will post if the problem returns, as I say it doesn't happen often, and won't ever last the day, just for intermittent relatively short periods.

Shaun.

[Active Rascal]

Update,

As I posted, bike ran fine yesterday no problems at all. Today I washed it, started up..... took a good few kicks, ran OK, let it warm up then the misfire developed.

I noticed that the carb breather that's near the fuel inlet was missing, and maybe water had got into the carb? I drained float bowl and ran fuel through. Still misfired, this could have been just an unfortunate coincidence? This wasnt missing before I went out yesterday.

Took out plug, was a bit sooty, but not too bad, spark appeared strong and good. Returned plug and started up, error consistent.

I also bypassed both the ignition and kill switches and the problem still persisted, so neither of those.

I managed to take a video, as you can see it's a very flat exhaust note and has lost that high rev 'ting' which I normally hear. Also lots of smoke noted, in particular very dark smoke, almost like black smoke came out on the over run a little, cant be seen in the video.

http://www.youtube.com/watch?v=B5IQoI0B ... e=youtu.be

Any clues or more ideas??

[knackeredMk1]

This might sound a bit odd - Is the return side of the oil pump running smoothly .

Just take the cover off and observe........

[Active Rascal]

That's a very good shout, but every time I've set up the oil pump or cables it's been fine. I certainly will check again.

Is the PV sticking shut a possibility?

Just sent the video to a mate, he said it's like it's 4-stroking, and running very rich. Not sure what would make it like this intermittently, as usually it runs really crisp and clean.

As I say in the video it is ticking over nicely, when it misses on the lanes it doesn't always tick over.

[helisupp]

At some point in this thread you will have to CHANGE something, as until you do there is no process of elimination.

One thing will happen for sure if you do not, it will happen again and again. If a fault goes away on its own, it usually comes back on its own.

Change carb, change coil...........both then eliminated, next change PV controller, ECU.............both then eliminated.

Then we can start looking at sticking PV, Clean it, then thats eliminated.

[Active Rascal]

The carb has a special sleeve machined and bonded to the air filter side to compensate for the larger CR air intake, so not really easy to change a carb.

Have a spare standard ECU.... but reluctant to try it as I don't know enough about the problem and don't want two duff ECU's if this turns out to be the problem. Current ECU is Mugen.

I agree with what you're saying entirely, however don't want to start chucking money in, would rather know more about what's most likely the cause prior to full investigation. Also it's very difficult to get to things on this bike unfortunately.

There's a relay behind the headlight which had water in the connections after washing, but not even sure what the relay is or does. The relay is sealed but the plug isn't. I'll start by looking at this......

Cheers.

[Active Rascal]

At the workshop now. It is the powervalve. Please don't say ECU again