Advice on my Plug Chop pics please.

[Royston]

Hey guys,

Hope you can help me please. I'm sure I know the answer to this but I'd just like some reassurance please before I kill my top end.

I have just fitted a PWK33 on my 212cc stroker motor and when I'm WOT flat out (and sometimes when when I whack it wide open) I get a bit of a stumble/misfire/blubber. It feels like I'm rich which makes sense but my plug chop doesn't look as rich as I expected:

To me this looks slightly rich but I wouldn't have thought I'd get such a pronounced misfire @ ~8 - 8.5k rpms.

I've gone down one size and I'll try again but I've ordered the next two sizes down as well.

I just wanted to get some feedback from you guys please coz looking @ the other plug chop threads on here I'm not sure if it's rich enough to cause the problem I've got or whether I should be looking at another issue going on.


Thanks

 

[Awk08]

I can't recall anyone running a 178 main jet. that does seem rich, as the plug shows a black ring, your looking for cardboard colored.
but keep temp drops in mind, jetted right on the line may fry at 20-30 degrees colder temps.

 

[Royston]

Thanks for the reply. That's exactly what I needed to hear.
I will go down 1 size at a time and test. And I'll keep an eye on ambient temperature.
This is built only for road riding so I'm wide open for extended periods. So I know I gotta be careful but I can't sit full throttle atm coz it breaks up.

Thanks

 

[Royston]

Thanks for the advice Awk. I went down to a 172 and now it revs upto the limiter (10.5k) scary fast. Its about as cold as I'm happy to ride here atm (5*C) so I'll plug chop tomorrow to see how it's looking

 

[Royston]

So I'm down to 170 now and looking like this:

Definitely better but I still get an intermittent stumble at about 8.5k before it takes off again to 10k or so. It's come back since the weather is slightly warmer (~10*C)

So I'm thinking I'm still good to keep going down?

Other than this stumble and being intentionally rich on the needle straight, it rides great.

Thanks


EDIT:

This is resolved now.
Went down to a 165 and added more timing advance between 8k & 10k.

 

[Larry's Shee]

Try leaning air screw a hair. If not better return to original and lean needle one clip

 

[Larry's Shee]

Did it seem to run worse when weather is warmer?

 

[Royston]

Yeah it seemed okay when it was cold (5C) on a 172, then it warmed up a bit (10C) and a plug chop on a 170 looked just like the 172 but sometimes held back at around 8.5k. So I went to a 165 (and added some timing advance at the top - not sure if that's made any difference) and then it would rev into the 9s every time without hesitating @ 12C. I pulled the plug and looked down at the smoke ring and its still brown but I didn't chop it coz I'm out of plugs.

 

[Royston]

Merry Christmas BTW!