Kymco 300 Maxxer misfires when hot.

[sidyid]

Hi Guys, having looked through the past posts none of it is relevant to this issue....
I operate an activity centre in Southern Spain and our most popular activity is quad bike tours on a nature reserve (slow, nature ramble on wheels tours for 20 years).
I have a Kymco 300 Maxxer, it started to misfire when hot.
Recently (through last winter) I completed the following jobs....
New barrel and piston, I now have 200 plus compression.
New valves.
Tappet adjust.
New Cam chain.
New oil pump and chain.
New gear change control unit.
New CDI unit.
New coil and ht lead.
New battery.
New carb.
Full service.
I have 18 of these quads (Maxxer, KXR and MXUs).

I have completed parts swap overs with running quads and still have the issue, however, it starts right up without and problems and only starts to misfire when it is hot (Southern Spain).
Do any of you guys have any idea at all what it might be Please?

[Iahawk]

did the misfire occur before you did all the engine work or after? You've replaced so much...air or vacuum leak? Clogged air filter? timing off?

[randyo]

what octane fuel are you running ?

my K-pipe will run on anything in cooler weather, in the heat of summer it needs premium

[Stig / Major Tom]

Octane question in the heat was my thought, too.
Plug heat range....?
Stig

[JJJoseph]

I have completed parts swap overs with running quads and still have the issue, however, it starts right up without and problems and only starts to misfire when it is hot (Southern Spain).
Do any of you guys have any idea at all what it might be Please?

Stators don't last forever, and if one of the coils develops a short it will stumble at higher power settings.  They will fool you because the machine will start and run normally.  It will misfire at higher power setting when hot.  You need a flywheel removal socket to change the stator.  Otherwise it's not a complicated fix. Takes about an hour to replace.

[Ruffus]

Late to party, but: since I had this lately.
Check fuel pump and fuelpump relais.
Gets tricky when hot.
As JJJ says, check stator too (3x yellow)

Pls see link
https://www.kymcoforum.com/index.php?topic=34331.0

[JJJoseph]

I just thought of something else to check!  Most Kymcos have a tiny little check-ball in the fuel filler cap to prevent gas vapors from exiting from the fuel tank.  If the little check ball sticks closed, there'll be a slight vaccuum in the tank & your fuel flow will be stifled.  It's like you've briefly run out of gas.  You can quickly verify when the machine is misfiring: your inline see-thru fuel filter will be empty. Then will slowly fill up again.  I remove the little check-ball and toss it, even though it contributes to global warming. I feel guilty for a day or so, and then I get over it.