Yeah, do the plug check first. It's easy to do.
If your engine is stock condition, stock pipe, etc., start with the stock main jet. See how it runs. I can't comment on Yamalube, don't know anybody that uses it. Most of the people I know use Golden Spectro or Amsoil. Put your needle in the middle position. Start there. I, personally, like mine to smoke a little when reved, not a lot, just a little. I have the clip in the 3rd notch, run a 158 main jet, have an opened up airbox with a K&N, FMF pipe and silencer. This is good for dirt/trail. Dunes, I run a 160 main. Seems to work well for me. But, I started with everything in stock position, closed airbox, etc. Then for each thing I did, I adjusted for it. When I opened the airbox and added the pipe I went up 3 main jet sizes, etc. Check it out and have a good time and good luck.

 

raped ape, that is too much...

 

Sounds to me like your main jet is too rich.

 

Your main jet number sounds right if your quad is STOCK! If you have a CLYMER manual it gives ALL JETTING recommendations for the stock 250R(all years), I have the manual and that is why I said the Main jet size sounds about right. Before you lean the main jet and make a costly mistake, give us more info on your mods. I DO FEEL you need to run the BR8ES plug--gapped to 25-28 should be about right. Just by guessing, with the info you provided, it sounds like you may have a faulty component in your ignition. PLEASE BUY A CLYMER--you can't believe the amount of info it contains. It even has a trouble shooting guide!

 

20:1 is a rich mixture. i ran my r at 32:1 and it ran great also your jetting could be off.

 

you can't always go by plug readings because of todays gas be careful.

 

You shouldn't have to jet it out of the blue unless you did some other mods,or the weather has changed.