Ok I finally got my compleat Yoshi system. I set it as per their specs, (these are for sea level, I am a 4700 feet) at worst I thought I would be a little rich. When I started it up last night I ran it for about 5min, when I slowed down to check for any leaks I noticed a deep red glow from my head pipes, and a small inconsistant back fire.

I put in 150 and a 155 jet, added two 1 3/4 holes to the air box with no snorkel. This is as per Yoshi, (since I was running great with 140 and 145 jets, the factory jetting for sea level) I thought I would be ok with there set up.

My question is do I drop in bigger jets? ( if so how much bigger?)
or can I make some adjustments with my air fuel mix?

As for what Yoshi says, they ask me to leave a message, (no answer yet)

 

Set your fuel mixture screws 3 turns out and see if this helps. It worked for me. If it's still too lean you might need bigger pilots.

 

I finaly got info from Yoshi. They said with a K&N filter I should go to 160 and 165 on my jets. Has any one else bumped up to this jetting size?

 

My headpipe glows too and that is a normal feature of stainless steel. As for the backfire, that is not main jet related. It is controlled by the idle mixture jet. It is located, on my warrior, between the bore of the carb and the motor. It is on the bottom and is the only adjustable jet on the carb. Turn it out at 1/4 increments until the backfire goes away. If however, you go past 4 turns out, purchase a new slightly larger idle mixture jet. The main jet should only be changed if at 3/4 to full throttle the machine stumbles.

 

Yup, stainless Yosh will glow, if you remove the lid try using 165/170 mains, clips 3 or 4th pos. Also, an aftermarket pipe makes a 4 stroke sound like its backfiring on deacceleration but its normal. If they are real crisp & loud & only occur as the throttle is let off for a few secs then it is too lean on bottom & fuel screws should be set around 3 turns out each side. I have talked to many Yamaha techs who said leave the left side fuel screw set @ 3 turns out & adjust the right one accordingly for best idle/no backfiring on deacceleration. I adjust my right one depending on summer/winter air temps, you can actually hear the idle worsen when it needs to be adjusted. I can run the right one from 2.5 ... 3.5 turns & don't hear/notice much difference. I think some people put to much stock into the fuel screw settings!?