Jetting/spark plug?

[AntNZ]

So my bike was running sweet then started running like s#*t. Sourced the problem, spark plug buggered.
Decided to get cr7hix irridium plugs instead of c7hsa.
I have put new plug in and now bike starts first kick every time with choke and no throttle, once warm it idles perfect with choke off.
First thing i noticed was the exhaust started getting really hot and i could feel the excessive heat from it just sitting on the bike.
I took it for a ride anyway, it ran fine for half a lap of a track( 1.20-1.50min laps), then it started breaking down/stuttering at half throttle.
It revs clean off idle and once past the mid range stutter it revs good all the way to top.

Jetting is #39 pilot,#105 main, z155/160HO with stock engine.

Needle was 2nd from bottom so moved it to bottom position and it was better but once engine was hot same thing happened.

In the past when exhaust was hot like that jetting was too lean on the pilot.

Is a #41 pilot way too big for this engine...oooops sorry, it has OKO 26Flatty.

Could the new irridium plug be burning more fuel therefore needing more?

Cheers

 

[my67xr]

I would readjust the mixture screw and find out how many turn's out it like's to run at.
This should tell you if you need a bigger pilot jet or not, i reckon it might need to be somewhere around 1 turn out now that it has a decent spark plug.
If that's the case then fit your #41 pilot.
The stuttering at half throttle is from being too rich, i'd put the needle clip on the middle notch
You might even need to drop the main jet one size too, especially if you need to go bigger in the pilot jet

 

[AntNZ]

Cheers Craig, But the plug is looking lean!

 

[gottagetacheaperhobby]

Try a 108 main with needle in the middle, if its starting with choke and idling well after its warm with no rev hang the pilot circuit is fine.. being in nz im guessing its a fair bit colder than here in south aus atm, and cold air burns hotter, which would explain why you need a bigger main jet than most ppl here in aus..

Sent from my SM-T110 using Tapatalk

 

[AntNZ]

Try a 108 main with needle in the middle, if its starting with choke and idling well after its warm with no rev hang the pilot circuit is fine.. being in nz im guessing its a fair bit colder than here in south aus atm, and cold air burns hotter, which would explain why you need a bigger main jet than most ppl here in aus..

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Cheers, temp average here atm is round 12-15 deg even cooler in mornings and evenings, 5-10 deg.

I have a 108 main spare so i'll try that first and if that doesn't work i will try what Craig suggested.

Thanks again.