Mikuni TM28-1 Intake Boot Options - Page 2
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Thread: Mikuni TM28-1 Intake Boot Options

  1. #11
    Senior Member elime's Avatar
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    The bolt pattern is good and it fits the carburetor well. The only thing that is off is the intake port in the head -- it will have to be opened up, matched to the manifold. That is one possibility that may yield better performance. Or search for a better fitting manifold.

    P7030030.JPGP7030028 (2).JPG
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    Long live the internal combustion engine!

  2. #12
    Senior Member elime's Avatar
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    Quote Originally Posted by fishguy View Post
    elime - I know what you mean. I want to buy all this carb stuff and just might. A TW with a pumper should be interesting.
    If you are going to buy a carburetor that sits on the shelf may I suggest buying a cheap one.

    This is a picture of the carb that I linked to earlier. Also a picture of the cable -- it is a one into two arrangement. One end operates the slide and the other the accelerator pump.

    P7030027 (2).JPGP7030025 (4).JPGP7030026 (2).JPG
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    Long live the internal combustion engine!

  3. #13
    Junior Member squirrel's Avatar
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    Measuring the ID of the TM28-1 throat i get 28.91mm with my cheapy micrometer, and i get 28.81 on the intake port, so in my case they are well matched. I wonder if the gap inside the boot between the throat and intake port can be filled to maintain a smooth flow...

    I found this table
    Mikuni Flanes Dimensions.jpg
    Looks like the M-VM-34-200-K is my best bet.
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  5. #14
    Senior Member elime's Avatar
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    A year or more ago I found what I thought might be a good fit. It was an XT225 manifold but I am not real sure now that is correct. Anyway, I found that not all XT225 manifolds (if that is what it was) were the same plus they costs something like $40 or $50. I didn't feel like gambling that amount on a maybe so I moved on.
    Long live the internal combustion engine!

  6. #15
    Junior Member squirrel's Avatar
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    Thats my sentiments exactly, but luckily i managed to spot the part number on your photo and thought id take one for the team The dimensions are close enough and its straight so hopefully this will be the same one Palm State used for his carb mod. Should get it tomorrow or Saturday and will report back when i get some free time to check the fit.
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  7. #16
    Senior Member Cornelis's Avatar
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    I hope this will help you with your project -

    I have this photo of mrbrackets TM28 Pumper Carb mounted onto his bike which I saved to my hard drive. The photo is not available on tw200forum.com any more but if you still want to read the post CLICK HERE - MrBracket's TW200 Build the photo was at post #375

    1990 Yamaha TW200Hidden Content _____________ Come to Me, all you who are weary and burdened, and I will give you rest. - Matthew 11:28
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  8. #17
    Senior Member Fred's Avatar
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    Note the Lamba (?) sensor on Mr.Brackets exhuast manifold. Despite being able to read accurate air/fuel ratios throughout rpm range I believe he never achieved optimal jetting. I believe his project was subsequently abandoned. Similarly I do not recall a favorable post-jetting report from PalmStateCrawler.
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  9. #18
    Senior Member Cornelis's Avatar
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    I found this post about his final conclusion with regards to the TM28-1 carb -

    Quote Originally Posted by mrbracket View Post
    On my 1994 TW with the TM28-1 carb, a #110 jet, #20 pilot, and 5DP39 needle in the 4th groove worked the best. "Best" being defined and good throttle response, best top speed, and an average AFR between 12.5 and 14.0

    However, when I moved the carb onto Mr. ProCycle's 2001 TW, the jetting didn't work as well. His bike needs richer jetting. I suspect my bike has many more miles on it and has less compression?? His bike is also faster than mine, I can get up to speed and maintain a faster speed on his up hills...

    Every bike is a little different, we all will have to jet for our own bike and elevation. No single jetting setup will work for everyone...

    Hope that helps.
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  10. #19
    Senior Member Cornelis's Avatar
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    Woohoo! I am completely sold out for this thing, just look at the graph!

    Quote Originally Posted by mrbracket View Post
    Finally some new information!! Whew, I've been slammed lately and not been tuning the Tdub all that much. I spent some time on the dyno today!!!



    The blue HP and Torque lines are from the best run I had with the tuned stock carb and stock exhaust. The orange lines are from today with the TM28-1 and DG exhaust..

    The graph shows that the open exhaust and bigger carb allow the engine to pull harder and longer on the top end. What the graph does not show is how the pumper element of the carb gives it more throttle response at the bottom.

    The graph today starts at 4000rpm because that's the earliest I could open the throttle to Wide Open while in 5th gear. I could open the stock carb wide open at 3000rpm in 5th gear because it is smaller and flow less air.
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  11. #20
    Senior Member renny10n's Avatar
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    Quote Originally Posted by Cornelis View Post
    I hope this will help you with your project -

    I have this photo of mrbrackets TM28 Pumper Carb mounted onto his bike which I saved to my hard drive. The photo is not available on tw200forum.com any more but if you still want to read the post CLICK HERE - MrBracket's TW200 Build the photo was at post #375

    -----------------------------------------------------------
    That carb looks more of the 2 stroke tm28 flat slide design and not the tm28-1 pumper? ....or did the TM28- 1 pumper have a different throttle cable design than the TM33-1 pumper? There is no additional photo showing the right side of the above carb showing the accelerator pump. So, can someone enlighten me please,. Cause I do have a new TM33-1 pumper(from another project) and it has a totally different and taller top cover and it has the throttle bracket and pull/push cable wheel/cam on the right side.

    Interesting, Tumbleweed has a post of running the TM28-1 on his TW250 race bike and one of his final thoughts was, that he thought the TM33-1 pumper might be a better carb for the Tdub. That being said, has anyone compared measurements of the TM28-1 & 33-1?
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