Ok, I have an 86 250r. I got a new motor for it last weekend and when I got home, rejetted it. It would cut out badly in the top end, just kinda sputtering top end instead of running. It did this especially in 1st and 2nd gear. I thought it was rich and so I went down from a 155 main to a 152 main jet. I also moved the needle clip down 1 position, from the 4th (last) to the 3rd (next to last) position.
Today, I rode it and it was still cutting out, only now worse, now instead of mainly 1st and 2nd, now its 3rd as well. So I ran it hard across the yard and fouled a plug. I changed plugs, and it still did it. I pulled up to the garage and noticed that it was smoking BAD BAD BAD! There was a trail of smoke behind me I could see everywhere I had been. This smoke smelled really hot, not just like normal 2-stroke smell.
Please help, what did I do? I am stumped.

Thanks

 

If the plug is fouling out the carb is set too rich. What ratio are you using for fuel as well?

Try reading the following articles:

http://bombardierds650.com/techtips/jettingguide.htm

http://bombardierds650.com/techtips/sparkplugs.htm

 

On erery 250r that we have built. The clip is either in the top or next to top grove. We run any were from a 152 to a 158 main jet depending on the amount of engine work done on a stock cyclinder. When you mix your gas go with 32 or around 40 to 1. Done do the 20 to 1 like it says on the quad.
Did I read it right that you want to put a bigfoot kit on a 250r? Why?

 

Ok, well half of the replies to this thing got somehow deleted. Anyway...I took it to my mechanic and he thinks it blew a crank seal. It was smoking way to badly to be improper jetting, especially when it had run ok on the 155 main and I went down to a 152!
I am running my premix at 40:1 as well.
And as for the bigfoot kit, no...if you read a little more closely its for a 300 4X4. Dont think it would work too well on the R!!