Mikuni TM 41mm Pro w/ powerjet
Posted: January 18th, 2008, 2:57 pm
Ok, let me start from the begining. I helped a friend put a showmobile motor in a honda odyssey and he wanted to pay me. I wasn't going to take his money especially after how much of that tire tread I left stuck to the street in front of my house (the thing would wheelie if you finessed it just right and moved your legs back ). But he had a box of carbs that I was willing take off his hands. We originally put 2 mikuni pro 39mm carbs on the yamaha 440 motor, but it was a bit too much carb and had better luck with 2 PWK 35mm carbs. so those 2 carbs were included in the box. Mukuni makes 2 models of their TM38, I believe they are called #85 and #86, the only difference between the 2 is the outside diameter of the mounting flange. One is 43mm and the other is 47mm. Well, the TM 39mm Pro carbs from sudco are built on the 43mm body, so you don't have much room to bore it anymore. Sudco uses the 47mm body to make the 41mm pro. in the box with the 2 39mm pros were 2 38mm carbs, one of which had the 47mm body, but didn't have all the cool features of the pro series (mounting pad for powerjet, larger inlet valve and a couple of other things I can't remember). well, the body splits into 2 peices, the front and rear. I took the rear off one of the pro series, stripped the carb down and took it to my machinist buddy and had him bore the assembly to 41mm.
I then reassembeled the whole thing with all the shiney new pro series parts. I called sudco for the default jetting, bought the right needle and the power jet kit.
Talking to both Glen from GSS and DeWayne Jones (both encyclopedias of cr500 knowledge), they both said they love that carb and run it themselves. I had dewayne even give me his current jetting specs for a reference (he runs the same carb on his personal supertt race bike).
I set it up with a 50 pilot, r-2 needle jet 6fj41 needle, 340 main and 120 power.
It was a bit hard to start (that needle is a little lean), but once I got it started, it ran TITS! Installation was a breaze, the throttle cable was a little too short, so I fixed that, and its a little tall, which makes it a bit cumbersome, but it fit perfectly in both boots, infact it doesn't look like it, but it fits in the air boot all the way to the stopper in the back. Actually easier to install than the pwk because its slightly shorter.
the idle screw is hard to get to, and the fuel inlet is on the other side.
The power improvement over my pwk 39.5 was very noticeable! I had everyone telling me that it was less responsive at part throttle, but it couldn't be further from the truth. 1/8-1/4 amazed me...it was wheelie time!
I still need to do some fine tuning, but my out of box tuning already out performs my pwk. I rolled on the throttle slowly and it just kept picking up the front wheel as I was opening it. I could feel after holding it open for a while, the power jet kick in and the next thing you know, my over rev was going through the roof. the power jet was too rich though and blubbered a little.
all in all, I couldn't be happier and can't wait to see how it does in the dirt.
here are some pics, I'm going to get an elbow for that fuel line.
I then reassembeled the whole thing with all the shiney new pro series parts. I called sudco for the default jetting, bought the right needle and the power jet kit.
Talking to both Glen from GSS and DeWayne Jones (both encyclopedias of cr500 knowledge), they both said they love that carb and run it themselves. I had dewayne even give me his current jetting specs for a reference (he runs the same carb on his personal supertt race bike).
I set it up with a 50 pilot, r-2 needle jet 6fj41 needle, 340 main and 120 power.
It was a bit hard to start (that needle is a little lean), but once I got it started, it ran TITS! Installation was a breaze, the throttle cable was a little too short, so I fixed that, and its a little tall, which makes it a bit cumbersome, but it fit perfectly in both boots, infact it doesn't look like it, but it fits in the air boot all the way to the stopper in the back. Actually easier to install than the pwk because its slightly shorter.
the idle screw is hard to get to, and the fuel inlet is on the other side.
The power improvement over my pwk 39.5 was very noticeable! I had everyone telling me that it was less responsive at part throttle, but it couldn't be further from the truth. 1/8-1/4 amazed me...it was wheelie time!
I still need to do some fine tuning, but my out of box tuning already out performs my pwk. I rolled on the throttle slowly and it just kept picking up the front wheel as I was opening it. I could feel after holding it open for a while, the power jet kick in and the next thing you know, my over rev was going through the roof. the power jet was too rich though and blubbered a little.
all in all, I couldn't be happier and can't wait to see how it does in the dirt.
here are some pics, I'm going to get an elbow for that fuel line.