ID this carb

Discussion in 'Airheads' started by walkingbear, Jan 20, 2013.

  1. walkingbear

    walkingbear Lets Play Chicken!

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    [​IMG]
    #1
  2. bmwrench

    bmwrench Long timer

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    Who did that intake port/stub?
    #2
  3. bpeckm

    bpeckm Grin!

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    I like the way they did the valve cover fastener, too... the standard is a stud with a little 10mm nut and washer tucked up behind the head... tough on fat fingers....

    :eek1
    #3
  4. Airhead Wrangler

    Airhead Wrangler Long timer

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    Looks like a Mikuni HSR model.
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  5. Big Bamboo

    Big Bamboo Aircooled & Sunbaked

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  6. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    Question is why-- look how small the exhaust pipe is.

    I say it's a bling...

    --Bill
    #6
  7. Houseoffubar

    Houseoffubar HoFmetalworks.com

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    Yeah, HSR, or RS model. RS is usually for multi cylinder bikes, so probably HSR
    #7
  8. Big Bamboo

    Big Bamboo Aircooled & Sunbaked

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    Looks are deceiving, that pipe is way down there (click on the pic): [​IMG]
    #8
  9. Big Bamboo

    Big Bamboo Aircooled & Sunbaked

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  10. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    AH, I see that now. Must have been a photographic perspective thingy. And that starter cover/airbox blockoff looks impressive. Neat and tidy job.

    Carry on... :D

    --Bill
    #10
  11. RGregor

    RGregor Been here awhile

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    This bike belongs to a friend.

    The carb is a Mikuni TM40.
    Header pipes are 38mm.
    Cover is self made (aluminium cast).
    Head modifications are self made.

    The valve cover fastener mod is quite usual over here.
    You can do the conversion on your own or by modified covers.
    Additionally you can insert a threaded bushing into the heads.
    #11
  12. England-Kev

    England-Kev Long timer

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    Oh yes!:D
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  13. supershaft

    supershaft because I can

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    The carbs are bling? I wouldn't run those but they do work! I would say the gas line is bling. Braided? No cross over? I have my doubts about the port mods too but you never really know until you try it.

    I wonder if people that do that valve cover mod usually strip out the threads? Most that I work on that have that mod still have the nuts on the back side. Kinda ruins the whole point IMO. It actually makes the setup an even bigger PITA IMO.
    #13
  14. Airhead Wrangler

    Airhead Wrangler Long timer

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    Maybe not the carbs themselves, but the fact that he went to quite a bit of trouble to polish the hell out of them maybe. TM40s aren't usually that shiny.

    [​IMG]
    #14
  15. supershaft

    supershaft because I can

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    That I knew. I am familiar with those carbs since a lot of people ran them on their Rotax powered short track bikes. Awesome carb on those engines!!
    #15
  16. RGregor

    RGregor Been here awhile

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    Polishing the carbs was done by a company. It did cost ~40€ for the pair. Don't remember exactly but it was cheap. I had my Dells polished there, too.

    The TM40s work good.
    Can't say if they perform better or worse than Dellortos. Not yet.
    Currently I'm running 38mm Dells, I wanted to switch to 40mm Dells and now got a new pair of TM40s for a very reasonable price.
    I'm planning to do some kind of cross-comparison for the three carbs on the dyno.
    #16
  17. Airhead Wrangler

    Airhead Wrangler Long timer

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    I like that idea. :nod

    Maybe you should test a bing as well. It'd be interesting to see the difference
    #17
  18. RGregor

    RGregor Been here awhile

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    Sorry, but I'm not interested in Bings ....
    Additionally it would mean quite some work to adapt the spigot (is that the right word? Anyway, mines are welded in) to the Bing with it's 42mm or 44mm throttle diameter.
    #18
  19. supershaft

    supershaft because I can

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    Sounds like a lot of work like we ever cared. At least the Dellorto's will jet damn near if not exactly alike I bet. Be sure and run a sniffer in order to help determine that you are not comparing jetting versus the carbs. As far as that carbs themselves are concerned, it sounds like you are going to compare them with the same spigots? The Mikuni might work best with an entirely different spigot but what works best with your setup is most important to you, of course. I suspect the biggest carb (the Mikuni) will make the most peak power. The tricky part is that peak power is just a small part of the rev range and first you have to GET there. The further you get away from peak power, the trickier getting reliable dyno readings get. Especially with wheel dynos. Carb tuning is SO much about just off idle and midrange. Wheel dyno's don't even do just off idle and midrange readings are so dependent on so many variables most serious tuners use engine dynos for that kind of testing and development. Unless one setup has a huge advantage that you can see on the dyno and feel on the bike, I would be more interested in what your butt dyno tells you about each carb setup. Some comparative lap times would be great too. When it comes to just off idle and midrange, what works best on the dyno very often isn't what works best outside of that room. The dyno contest winner won't be the fastest bike on the road or the track. Even if the track is a drag strip!
    #19
  20. RGregor

    RGregor Been here awhile

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    My butt dyno is the motivation to test different carbs.
    The engine is very strong at low and medium revs, but it feels as if the 38mm Dells already may be a bit small for high revs. Regarding the pure numbers from the chart the engine is strong at high revs also, but it doesn't feel aggressive enough for these numbers.
    Can't describe it better.
    I'll do the test without mechanical change just to get an impression, if that feeling is right.
    If there is an improvement I will decide how to get the best mechanical setup for the carb in question.
    And yes, I'll spend enough time to get a proper jetting for each carb and check F/A ratio with the sniffer.
    #20