Tri-z Jetting

[Rigaman]

my buddy has an 85.5 tri-z with a 320 main jet in the carb. My 85 has a 480 main jet. I am not sure what the stock main jet on an 85.5 is, but the stock main on an 86 is 320. What is so different between an 85 and an 86 that would make such a huge jump down in jet sizes from 85 to 86?

Would my 85 run good with a 320 main? I was under the impression not much changed in the engine from 85 to 86. I just dont get how it could be that much different.

[TimSr]

The 85.5 TriZ is an internet creation. There was one 85 YTZ250N with two color schemes. Since they ran the black and red scheme in the 2nd 85 run, it got nicknamed 85.5.

The 86 used the same carb as the 85, but they were trying to smooth out the light switch powerband by changing the midrange carburetion with a different needle, and needle jet which also necessitated a main jet change. If you change the main without changing the needle and needle jet, you will most likely end up running very lean. How does it run now? Stock on yours is 470, and my guess is its currently running way rich, like most TriZ's out there. Monitor and read your plug, and drop in increments of 10 until its right. Most run okay on the stock jetting, but you can get more out of it by fine tuning it down. If you want to go the 86 powerband route, its not worth the effort. Most people don't realize the needle and needle jet were far more significant than the main jet change, or that they are very different.

Your buddy's should also the same as yours. He probably either has an 86 carb setup from some previous owner, or somebody was confused between the years as to what it should be. How does his run?

[Rigaman]

His runs amazing. Or did before he blew it up. His vin shows his is actually an 86. I think he has an 85 motor though. He does have the 86 air box.. 86 carb.

[wisconsinite]

His runs amazing. Or did before he blew it up. His vin shows his is actually an 86. I think he has an 85 motor though. He does have the 86 air box.. 86 carb.

famous last words, lol. maybe he was running too lean. they do go like stink when you lean'em out.

[Rigaman]

Heh ya. His actually blew when the bolt holding the main crank gear in place shook loose, and it in turn stopped turning the water pump, which over heated it. It also pulled the crank seal right out. The main crank gear bolt was just sitting there on the bottom of the case when he pulled the clutch cover.

His is an 86 carb, with an 86 air box, and an 85 motor. Im not sure if it was running too lean. But it had more nut than my 85. I think he was running 50:1 too.