Mikuni TM 41mm Pro w/ powerjet

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dannygraves
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Mikuni TM 41mm Pro w/ powerjet

Post by dannygraves »

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 :roll: 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 :shock: ). 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.
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'09 kx450f 4-Poke
Gen-4 trail bike --SOLD--
Gen-3 badass trail/mx bike --SOLD--
Gen-1 built dunes bike --SOLD--
'05 klx110 --SOLD--
'95 pw80
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dannygraves
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Post by dannygraves »

my favorite thing about it (besides the just plain more modern looking design) is the needle jet setup. I have 3 needle jets and 3 needles. All 3 needles are the same diameter, but a different taper, and the 3 needle jets are different diameters. it gives you so many more tuning options.
picture having 3 needles, like a cgn, dgn and egn, then being able to change the diameter to how ever many different sized you want. like if you like the taper of the D series needle, you could richen or lean it with the jet needle and make it the equivalent of a DGM, DGO, DGL, DGK and so on. its really awesome all the tuning options it presents.
'09 kx450f 4-Poke
Gen-4 trail bike --SOLD--
Gen-3 badass trail/mx bike --SOLD--
Gen-1 built dunes bike --SOLD--
'05 klx110 --SOLD--
'95 pw80
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britincali
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Post by britincali »

Sounds great :D
Coolness list by 90cr500guy

Bob's = 50/50
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aloha450x
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Post by aloha450x »

whatcha gonna do with your pwk? hummmmmmmmmm lol :roll:
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lewisclan
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Post by lewisclan »

YEAH WHAT? just kidding : bling :, Hey danny get that carb diled in as I have a new 41 pro also I am just afraid of not getting it diled and burning a pistion but I would like to run it on one of my hillclimbers maybe next time we meet at Dumont what do you think?
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AlisoBob
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Post by AlisoBob »

Good info Danny....
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dannygraves
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Post by dannygraves »

Jay, when I get it fully dialed, I will get you all the specs. Do you have the powerjet for yours? if not, get it, they are like $25 and come with everything needed including 3 jets for it.
DeWayne gave me all the specs he runs his at, but he runs an 80:1 mix, so I'm just using his specs as a rough guidline to get mine going.
'09 kx450f 4-Poke
Gen-4 trail bike --SOLD--
Gen-3 badass trail/mx bike --SOLD--
Gen-1 built dunes bike --SOLD--
'05 klx110 --SOLD--
'95 pw80
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dannygraves
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Post by dannygraves »

AlisoBob wrote:Good info Danny....
Thx, yeah, I found it very discouraging for me to run the carb with the lack of info out there about running it on a cr500. But Glen gave me some good advise and Dewayne helped me with a starting point and I want to help future hoons not fear running a different carb.
'09 kx450f 4-Poke
Gen-4 trail bike --SOLD--
Gen-3 badass trail/mx bike --SOLD--
Gen-1 built dunes bike --SOLD--
'05 klx110 --SOLD--
'95 pw80
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dannygraves
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Post by dannygraves »

aloha450x wrote:whatcha gonna do with your pwk? hummmmmmmmmm lol :roll:
hehe, sorry, IF I choose to get rid of it, my cousin (hoofarted) gets dibs.
'09 kx450f 4-Poke
Gen-4 trail bike --SOLD--
Gen-3 badass trail/mx bike --SOLD--
Gen-1 built dunes bike --SOLD--
'05 klx110 --SOLD--
'95 pw80
Image
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lewisclan
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Post by lewisclan »

THERE IS ONE ON THE OTHER SITE FOR $70
Image"the game of life of is not so much in holding a good hand as playing a poor hand well"
ou812
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Post by ou812 »

I you like that one you would love this one, this is the Boswell version, modiffied inturnals and reshaped intake and completly differant outlet, does require a 48 intake manifold to work , throat is a 40.5 . They sold for around $400 when you could get them. This one is still brand new.

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dannygraves
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Post by dannygraves »

nice!
:shock:
'09 kx450f 4-Poke
Gen-4 trail bike --SOLD--
Gen-3 badass trail/mx bike --SOLD--
Gen-1 built dunes bike --SOLD--
'05 klx110 --SOLD--
'95 pw80
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ISBB
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Post by ISBB »

is there someone that makes one of these out of the box applications or do you have to find 2 diff carbs and modify them to work properly?
97 Steel 500 that wants to be an AFC
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dannygraves
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Post by dannygraves »

sudco sells this carb. like $300.
'09 kx450f 4-Poke
Gen-4 trail bike --SOLD--
Gen-3 badass trail/mx bike --SOLD--
Gen-1 built dunes bike --SOLD--
'05 klx110 --SOLD--
'95 pw80
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ISBB
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Post by ISBB »

is it a custom carb or something that can be found on say ebay off some other form of bike or motor?
97 Steel 500 that wants to be an AFC
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dannygraves
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Post by dannygraves »

they make 2 different types of mikuni tm38. one has a 43mm outlet and one a 47mm outlet. they are numbered 85 and 86 I believe. the 43mm outlet one can be bored to 39mm, the 47mm one can be bored out to 41mm. you can tell with the naked eye by looking at it which it is because the 43mm (more common) look like the outlet where the airboot is machined down from the rest of the housing where the 47mm comes strait out. you can either bore a 47mm outlet 38mm carb or order a complete 41mm pro series from sudco for $300. I'd go with sudco, it has a different needle and seat setup to flow more fuel into the bowl and for sure comes with the mounting tab for the power jet. then its just an additional $20 for the powerjet kit. if you do get a sudco one, get the 6fj40 needle, 330-350 main jet and a 50 pilot. should be a good base line with the standard r-2 needle jet.
also I believe all banned members get a discount, ask for John.
'09 kx450f 4-Poke
Gen-4 trail bike --SOLD--
Gen-3 badass trail/mx bike --SOLD--
Gen-1 built dunes bike --SOLD--
'05 klx110 --SOLD--
'95 pw80
Image
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dannygraves
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Location: Las Vegas, NV

Post by dannygraves »

this diagram shoudl better explain what I am talkifn about
Image
'09 kx450f 4-Poke
Gen-4 trail bike --SOLD--
Gen-3 badass trail/mx bike --SOLD--
Gen-1 built dunes bike --SOLD--
'05 klx110 --SOLD--
'95 pw80
Image
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