Does anyone know what changes the AC 650 has in the powerplant over the Prairie 650?

The stock jets for the P650 are 138 front, 142 rear. I pulled the jets out of my AC 650, and
they are 122 front and rear. I'm a little confused, since they are quite a bit smaller!

I was re-jetting, and I tried the 138/142 and it seems to run super rich. Right now I have the Dynojet 124/128 in, but it still seems pretty rich when just reving it up.

Should the engine rev easily from idle to full thottle with no load? I was thinking of leaning it out a bit more, because it seems to labor a bit before it reaches full throttle.

 

Turns out that the inlet to the stock airbox is 2" in diameter (that's huge for the engine), but the snorkle immediately shrinks to 1 5/8" (21% smaller in area than the combined carb area). The Prairie 650 doesn't suffer like we do.....

I removed the snorkle, and increased the jets to 21% bigger. Turns out that places it right where Dynojet recommends the Prairie to be.

I haven't taken it to the trails yet, but 21% more fuel should give 21% more HP. That'll be sweet. I found that it pulled hard until about 65 kph, and then the acceleration flatline (obviously due to limited air intake).


To replace the snorkle, I wrapped about 6 turns of black tape around the inlet to the box. Then, bough 2 - 2" ABS plumbing fittings. One a 90 degree (female-female ends), one 45 degree (male-female ends). With the black tape on the inlet, the 90 degree forces on fairly tight (that one points straight up). The 45 degree plugs into the 90 degree, and points towards the back of the bike. This all fits under the stock airbox fairing. It cost about $2 bucks, and it puts about 7 HP back into the engine......