bigfoot

Here is the description from SLP's website, notice it says mikuni round slide carbs: The UFO is a simple, trouble free, aerodynamic piece that fits Mikuni carbs from 32 to 44 mm. The UFO makes a normal round slide carb outperform the more expensive flat slide carb by eliminating turbulence and increasing air flow and velocity, creating a highly atomized fuel charge. Normal gains are 3/4 to 1 HP per 100 cc of engine displacement. (Rejetting and tuning are required). Without the UFO, air hits the forward wall of slide cavity creating a rolling air turbulence forcing poorly atomized fuel droplets to the lower portion of carb bore resulting in poor fuel atomization and performance. With the aerodynamic UFO filling the slide cavity, the rolling air turbulence is eliminated. The higher velocity air flow pulls the fuel further up the needle and higher in the carburetor bore resulting in superior fuel atomization.

because they make different sizes for different size carbs and slide cutaways.....

QUOTE (FireHead @ Jul 8 2008, 10:08 AM) * This is another one of those products that improve performance by covering up a problem in stead of fixing it. If your engine was jetted and ported properly, this product will only hinder performance. geek.gif Not true, the UFO fixes a problem inherent to the round slide mikuni carburetor. The void at the bottom of the slide causes alot of turbulence, especially at low throttle openings. The UFO fills this void, eliminating the turbulence, and strengthening the vacuum signal at the carb, this is the reason for halving the pilot as a starting point, and the reason for big gains in the low end and mid, but mild gains on top. If you don't believe pull the slide out of round slide mikuni, look at the bottom of it, then think of it in terms of air flowing through carburetor, you'll understand immediately. If you put one in just make sure you install the correct cutaway ufo in the slide.

I've run these in sleds before, even an older yz 250 once. they work well. Halving the pilot is a rich starting point, it's likely you will go even lower. They make the biggest gains in the mid to lowend. A great mod when tuned correctly.