btodd

What do you think about the 39 PWK as compared to the 38 PJ that I have? I can tell you that I am sick to death of trying to dial this carb in. It seems much more "touchy" than the Mikuni that it replaced 3 years ago. I ask you because I have been thinking of stepping up to a different carb. Do they use the same types of jets (pilot, needle, main, slide)?

 

I was VERY impressed with the PWK from the instant I installed it. Compared to the stocker, it seemed to improve the entire powerband. The PWK was less finicky for me to jet than the stock carb. Part of the reason I got rid of the stocker was I could never find a happy medium between blubbery rich and burn-down lean. That was a number of years ago and I have since become more educated on jetting.

Not long after changing out the carburetor, I switched my pipe from a PSI to a Paul Turner and noticed another equally impressive increase in the powerband. This was especially true up top. It would really open up after this installation, whereas before, it would die out as the rpm's climbed.

The Duncan Racing catalog I have explains the difference between the PJ and PWK carburetors. It claims The PJ enhances low end and midrange power while the PWK is used for midrange and top end power. Duncan recommends the 39mm PWK for the LT500R. The reason is obvious. The big LT already has plenty of low end compared to other atvs but it somewhat "falls on its face" at the top end. The PWK is meant to remedy some of this problem.

As far as interchangable parts with the PJ, I can't answer that question for you. I am quite sure that the slide isn't the same. The main difference between carburetors (besides the size) is the slide. Keihin wouldn't sell two differently named carbs that had the same slide and nearly the same size. However, the jets and needle could very likely be the interchangable.

 

btodd
I think I'm on to something here. I am running the '87 jetting in my carb, main jet of 420, on my '88 cylinder which utilizes a 350 as its stock jet. During this last rebuild I replaced my '87 cylinder with my '88 due to the alleged head problems.

Does that 39PWK cost about $200.00? How hard is it to set up with my application? I noticed you said something about the stock "Zilla carb. being a pain to dial in. If a $200.00 investment will fix that problem, I'm all for it. I love this bike and nothing else comes close to it so I'm willing to do whatever it takes.

 

First of all, I want to get something straight. I said that I had an easier time jetting the PWK than I did the old TM but that may not be universally true. Many other people may be able to jet the TM just as easily. I am only telling you what my experiences have been.

Now I'm am going to make a few suggestions reguarding the purchase of a PWK and you can pick the one you want (or ignore them all). First of all, when I got mine, I shopped around to get the best price on a new one (approximately 4-5 years ago) and picked one up for $185 plus shipping. If you go for the lowest price, however, the service is going to suffer. What I mean by that is, the carb may not come to you properly jetted and ready to go (they may say it is but what kind of expertise do you think you are getting from a bargan basement dealer). Unless you know alot about jetting and are willing to take the time to do the testing yourself, you are better off going with a well known performance shop. Duncan Racing is a good example. You simply place your order, tell them what your current performance upgrades are, and out to you comes a carb ready to bolt on and go. I am not saying that it will necessarily be jetted spot-on but it will be very close. This service comes with a price. I believe the cost from Duncan back when I was shopping for the PWK was $225. The piece of mind you get, though, may make the price increase worth it.

If you just want to get the cheapest 39mm PWK you can find and then worry about jetting later, I would suggest a used one. Carburetors seem to lose their value at an astonishing rate. The domestic made Polaris snowmobile twin engines used to be fed by 39mm PWK's (I believe the 2001 or 2002's went to Mikuni TMX's). Go to www.amsnow.com and check out their swap-meet forum. You have to be a paying member to get into the good one so the limited one will have to do. Place a wanted ad and you are very likely to get some bites. I have done some carb shopping there (I'm a member) and, based on what I have seen, I bet you could pick up a good used one for $100. I don't mean to limit your used carb options to only that one forum. There are other snowmobile forums (www.snowmobilenews.com for example) as well as Ebay (I personally have seen them there). These are the avenues that come to mind but there are countless others.

 

Slinger, send me a SASE (self addressed stamped envelope) and I'll send you an article on jetting.
Jim Stapleton
12060 N. Oak Court, Azle, TX 76020.

In your post you mention "mid" throttle problem. This is a needle jet issue. A few basics: O to 1/4 throttle is controlled by the pilot (air) jet. 1/4 to 3/4 throttle is controlled by the neddle jet. 3/4 to full throttle is controlled by the main jet. Again, this is a very basic start to the art of jetting. It seems like you need to lean out out the neddle a bit. To do this raise the clip position, as this will located the needle further (lower) into the main jet, allowing less full. Again, a basic description. Not enough space or time to provide all the details. The article will help.

 

i wish i could get a quadzilla!![img]i/expressions/face-icon-small-sad.gif[/img]

 

I'll send an envelope. The thing that I have noticed is that the 87 cylinder calls for a main jet #420, which I have in my carb. The 88 cylinder calls for the carb to be jetted with a #350 main because of the reed cages having been changed after '87. I swapped from the 87 cyl. to the 88 cyl. creating a big disparity, I believe.

 

It's difficult to compare jetting between two quads/bikes, are no two are identical. My 1987 with stock bore, stock reeds, no porting, and Mikuni, I run a between a 360 main and a 380 depending on location, temps, etc. My 1988, on piston/bore P4, no porting, stock reeds, etc, and I use between a 380 and a 410. I use Uni Filters on each, no lid on airbox. My goal is to run rich, as this is safe. Once I get the needle jet set, the only jetting changes I make are main jets, and minor air screw adjustments. It's easier to change a main jet. The article will help.