what are you guys running (pilot jet,needle position,main jet) with the pwk 39 mm carb on trail mod engine on 400 2 stroke scrambler,also,is it clockwise to lean it out or counterclockwise to richen on the air screw?thanks.

 

Scramblered, my race-mod settings wouldn't help you, but I can tell you that turning the screw out leans the bottom end, and turning it in richens.

Ken

 

Scramblered, my race-mod settings wouldn't help you, but I can tell you that turning the screw out leans the bottom end, and turning it in richens.

Ken

 

maybe you're missing the point here,the keihin carb from what i've been told are turning it in mean leaner mixture and turning it out=richen mixture.this is not a mikuni...
can someone tell the needle/clip position also on HPD trail mod version?thanks.

 

Is it an air screw or fuel screw? There is a difference. The stock Mikuni uses an air screw. Turning an air screw out leans the mixture by allowing more air into the system, turning it in richens the mixture by cutting down on the amount of air that passes in. A fuel screw is just the opposite. Turning it out richens the mixture by letting more fuel in, turning it in leans the mixture by cutting off the amount of fuel that flows in. Which one do you have? I'm not sure without seeing it. The easiest way to tell is that if the screw is offset to the rear of the slide (center line of carb.) towards the airbox, it's a fuel screw. If it's offset to the front of the slide towards the engine like the stock Mikuni, it's an air screw. there was a great article on jetting in Dirt Wheels a couple of months ago. It explains this and a whole lot more in detail. I used to be afraid of jetting, but it's pretty simple if you have an understanding of how everything works.

 

No point missed at all here...if it's the same as the 39PWK I have that I sometimes run during the summer months...it's the exact same as adjusting a Mikuni. If you would like the micrometer readings off the modded needle I spent last summer dialing in, I can provide that to you also. I'm not the kind of person who likes it when someone says "I told you so", but I've given you my experience with the 39 in the northern tier, and if you already had some burndowns with a 42. I'm sorry to say, you're gonna be buying pistons. I'm not bashing the 39, just stating it has a harsher lean out.

Ken

 

you're right it is an fuel screw,wich mean turning it out richen the mixture,i have no problems on jetting at all,but it take always a starting point to get rid of this fine tuning.the deal is that i can't burndown down pistons with my pwk cauz i run dually dial-a-jet on it and it seem the pwk is pilot jet sensitive one.

 

The problem with the 39 isn't the pilot jet, but the 3/4 throttle to WOT transition. That's where the hot spot is.

Ken

 

it is because the pwk is CRISPER than any mikuni and take more ease on fine jetting the carb,no flat or hot spot at all here,the pwk scream a lot more on top end and keep going up the powerband more efficient than the 42 mikuni,but for sure the mikuni get some more power and torque,remember it is (42) a RACING carb only,i'm talking trail mod here.

 

The 42 is by no means a "Racing only" carb. People have been marketing, and using them for quite a few years on the 400. The different cut slide (greater angle for increased air), couple with the different needle, different taper to work out the "flat spot" really works with this carb. Living only 30 minutes from both Hot Seat and HPD, I have two great shops filled with lots of testing goin' on. Sometimes you have to weigh the info you get from the different sources, and try to form your own theories and testing for your particular environment. On this forum, and Bad Boys, myself, and some others spent a long time trying to help Xplor from up in your neck of the woods. By all means, give the 39 a try, I wish you the best of luck.

Ken