Needle advice

[Houghton]

Originally Posted by Jacob 'Berg

How is your compression? How many hours on your piston and rings?

This is where I would start if you can definitively rule out the carburetor and jetting.

Piston and rings are less than 10hrs and the bore is in good shape. The misfire was there before I changed the piston, at the time I thought it could be the cause.

[(F5)]

For giggles, because we're running out of ideas and new piston etc bring better compression, can you try a better gas, AV gas if you can get it easily, just to rule out that or season differences perhaps.
Obviously try new plug to see if any improvement. Check cap resistance or swap out.

Does it get worse as hot? Stator don't last forever. They get a little weird but usually heat breaks them worse.

[Houghton]

I Have just ordered a compression tester to confirm its ok but I'm pretty confident it is.
I have a new plug cap on there and I tried a hotter plug yesterday, that also made no difference.
I'm gunning 98 octane fuel, avgas is 100 I think so might be worth a try if I can get any.
I am now thinking the stator is the most likely cause.
I'd say it is getting worse, yesterday it wouldn't even wheelie in 1st, not because of lack of power but just won't rev through quick enough. It doesn't seem half as bad in the higher gears when under more load though. Strange.

[(F5)]

Wishing you luck. That's tricksy. My stator started doing odd stuff. It would micro die like if you were blipping over whoops you'd miss the timing of them. Then it got worse.
But they die in different ways/symptoms.

Took me a while to figure out the above, and I thought I was fairly clued up. Runs like a champ since then.
Saying that I'd hate to steer you into buying the wrong parts.

[blitz11]

Coil? They're cheap. https://www.ebay.com/itm/15583197638...EAAOSwljhlLQEH

Especially if the problem is when the bike is hot, it could be a coil.

[(F5)]

In dyno testing I've found some coils are better than others , but only really relevant to racing when everything else is at edge of compression etc.


. And I've certainly replaced them fault finding. I've found a few multi cylinder 4 stroke coils of the 80s fail.

But I can't honestly think of a cdi type failing. Usually what drives them. By all means swap out if you have one to hand, but don't arrange a ride thinking you've fixed it. Bit like the optimistic replacing the radiator cap when you really know the head gasket is blown.

[Houghton]

I have actually changed the coil, as it was way cheaper than the stator I started with it on that side of things.
To be honest it's no worse when hot. It's strange, it starts 1st or 2nd kick hot or cold, idles fine, makes good power on top but just runs crap everywhere else. Compression tester is due to arrive on Friday so I'll see what that brings..

Thanks again to everyone for the advice/suggestions, it's appreciated.

[(F5)]

You haven't left it for a while between tests? Or swapped in a blocked pilot jet between tests?
Will often start just fine but run badly.

[Houghton]

Originally Posted by (F5)

You haven't left it for a while between tests? Or swapped in a blocked pilot jet between tests?
Will often start just fine but run badly.

I don't think so. I have been right through the range of pilot jets all in the same day and there was no difference (to the specific misfire).I was pretty convinced it was a carb/jetting issue for a while, to the point I bought another carb, rebuilt it and went through all the jets again.

[webmaster]

Originally Posted by farmerj

Jeff, do you know what kind of modification Ron did to the pilot circuit? I have one of his carbs, and have always been curious about the "pilot sensitivity" part of his work (is it enlarging a passage or jet or ???).

Sorry, he wouldn't say. It was his "secret"...

jeff