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.

 

I haven't really seen a AC 650, but if it is same motor and carbs, the amount of air intake has to be different, for the difference in jets.

Get it some more air with the bigger jets. Most of the p650 owners have DG snorkels and larger jets.

 

motor wise the dif is nada as far as i know. your elevation will also factor into the jet size you need.

good luck
cart

 

I read a magazine test that said it felt tuned down compared to the Prairie.

 

The engine is the same,but it has its own airbox.The airbox is a little more restrictive. I tested it last week.It runs about the sameas a p650 with mud tires and steel wheels(surprise surprise). It has a little heavier body weight(independant susp,and more fuel,etc)as well as 26" heavier tires and heavier wheels. It performed best with our plain /purple secondary spring installed(same as 650 p),but preferred the blue primary spring(the same one we use on p650's with oversized tires),rather than the plain/white,which is our preference on a stock p650,as well as the p700. I guess it makes sense. The plain/white also performed better than stock,but the blue was more responsive with the larger tires and more weight. With the blue in it actually ran 2 mph faster on top end.
Tis AC650 is a Very impressive atv. I personally thought AC500 were a bit tippy,the 650 is(suspension wise )like a Polaris 6-700 series Sportsman(pretty stable).I enjoyed the ride,handling,mud protection.And you still have all that potential from the same kaw 650 engine.The 26"radials are very good all around tires. My whole time riding it ,my head kept thinking...with a holeshot module,web cams,a FST750 piston,airbox mods,...this thing could be the ultimate.

 

Hey wires:

Where are you doing most of your riding at and at what altitude? I'm from calgary but do all my riding in the Clearwater area just south of RockeyMountain House.The altitude there is approx. 4000'. I tried the DJ kit at 124/128 as well and found it to be too lean. Basically I got tired of trying to find the best jetting and went back to the stock 138/142 kehin jets, but would like to try again next spring.

 

I ride in the exact same area. I'll have to see when I take it out how it works.

What prompted the whole jetting issue is I read about punching holes in the airbox lid. I was reving up the engine (worked fine stock), and then I popped the airbox cover off. The engine would barely rev off idle.

So I figured it's super restrictive with the snorkle, and I pulled off the stock snorkle, replaced it with a couple of ABS 2" elbows. Right now with the DJ kit in, it works way better in the midrange (I had to use the 6th notch though to get it to rev up decently in neutral -- I'll verify that more when I ride it). So when I used the 124/128 DJ needles, it still seemed rich. Right now I have 122/124 jets in (the smallest the kit had).

So, that's why I was wondering about the engine. The stock jets are equivalent to DJ 116, which are really tiny! Opening up the airbox allows a P650 to go from 138/142 jets to a couple sizes bigger. I could never use the 138 jets with the airbox lid off.......

Weird and confused. [img]i/expressions/face-icon-small-smile.gif[/img]

 

Turns out, if I grunt the numbers, my AC650 is jetted (stock) to flow 30% less fuel through the main jets than a stock P650.

I checked the intake, and the airbox has a 2" diameter hole (that's more than enough air for 2 - 32mm carbs), but the snorkel drops the diameter to 1 5/8". That ends up being 21% too small.

If I work out jets that are 21% larger, that would put me right where DJ recommends them to be for a P650.

My exhaust is the same as a P650 I believe (the muffler is stamped "Nelson 28472 Spark Arrestor"), so my problem must be the intake.

I have a question for all you Prairie guys..... If you leave your bike in neutral, and pin the throttle. Does the engine rev smoothly to red line, or does it labor at the high end, and smell really rich? Just wondering if I biased my results wrong, since I was jetting it, and unable to take it for a spin before......

 

mine reves out fine in neutral

you need to get your intake worked out. big jets and more air equal BIG power gains.

the ac feels detuned cause it weighs like 80 more pounds.

 

Wires,
With the Kiehin carbs they like to have a rich fuel circuit. For one thing those DJ jets will not flow as much fuel as the OEM jets. The largest DJ jet in the kit is smaller in volume than the original jets that came with your machine. Open up the air box, replace the muffler with an after market one or drill 1/2 inch holes in the exhaust baffles. If you move the rear jet to the front and install a 145 in the rear carb you will be in the general area same as the Kawi group. If the jets are the same I think a few members have said their carbs have the same jets if so go with 142's straight across. You are right the motor does sound labored at higher rpms as the cdi is a major limiting factor. It has a basic soft limiter at 8200 rpm it will be hard pressed to rev higher than this number. To set your carb jets for your elevation I go with a rich system where I like to produce enough fuel over top of the carbs at full throttle your hand will be moist with fuel. The enriched fuel will flow to the roof of the air filter then be sucked back into the carbs this is the way they were designed. Good luck optimum exhaust temperature 2 inches away from the head is 1200*.