Airhead Mikuni Owners Thread

Discussion in 'Airheads' started by Uncle Pollo, Oct 2, 2012.

  1. Kt-88

    Kt-88 I like everything.

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    Ordered new brass from Bill at Rocky Point. What a difference!!

    For reference I have a 76 r90/6 with stock ignition and timing; nothing exceptional about the bike at all.

    Vm32 carbs
    30 idle
    I80 main
    6dh3 needles
    158-O8 needle jet
    Air screw 1 1/4 turn out

    With this set up the top end is incredible. I just want to go fast.
    Off idle is still just a bit rough, but only barely.

    All I want to do is ride this around now.
    #61
  2. oldroadie

    oldroadie Two wheel addict

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    That's good info; you're needle jet is .005mm smaller than mine but the rest is the same (except the motor displacement but I can take that into account)...and I'm at 900 ft. while you must be in the 4000 ft. range. That gives a nice baseline to judge changes from. What groove did your jet needle end up in?
    #62
  3. Kt-88

    Kt-88 I like everything.

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    Whoops. Forgot that bit! I put them in the middle to start with. Figured I would tune from there as necessary.
    #63
  4. Kt-88

    Kt-88 I like everything.

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    Not to flood this post, but I'll relate my freeway riding tonight.

    At the above mentioned settings and jetting, I can't redline 4th or 5th gear. First, second, and third feel pretty good, but WOT on the last two just never produced results. I mean, I was still doing 80 easily, but 2 k short and had ZERO acceleration capabilities. This leads me to think the mix is STILL rich on the main jet. I'll try lowering the needles tomorrow, and post results.
    #64
  5. Houseoffubar

    Houseoffubar HoFmetalworks.com

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    Lowering the needles at wide open throttle has ZERO effect on top end jetting. If you want to lean the carbs (which sounds like the right direction) you need smaller main jets.
    #65
  6. Kt-88

    Kt-88 I like everything.

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    Bet you're right. Bill was stocked out of 180s so he sent 185s. ...probably need 175s here, anyway.
    #66
  7. hardwaregrrl

    hardwaregrrl ignore list

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    That's what I'm running on my TM32's. 175 main.
    #67
  8. oldroadie

    oldroadie Two wheel addict

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    You should be able to get those mains right off the shelf at the local YamaHonda dealer. I have a pair of 170s in hand you can have...I had to get sets of four since that's what the local supply chain minimum is but the cost was small so I didn't mind.
    #68
  9. blaine.hale

    blaine.hale Long timer

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    Lightly reading through this thread for encouragement.
    What's to stop me from picking up standard Mikuni vm 34mm carbs for about $100 a piece and slaping them on the r90? I know I'll need proper jetting and cables, but what else comes in these mega expensive kits? Is it just the boots to fit to the existing BMW air filter?
    #69
  10. hardwaregrrl

    hardwaregrrl ignore list

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    Often times its cables as well. They're running 40$ for single or double pull. Obviously the single you would use the original cable to splitter, the custom splitter to the carb. They also come with a few main and pilot jets. Keep in mind Fred and I have a decent assortment if jets between us. Pilot main
    #70
  11. Airhead Wrangler

    Airhead Wrangler Long timer

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    Not sure what comes in the mega expensive kits, but you'll need to make different cables - not too tough. I think ordering the carbs prejetted from Sudco with the right settings works out cheaper than buying the carb with "standard" jetting and then buying all the correct jets, slides, and needles separately. I ordered mine with cables from a guy on Amazon selling them prejetted for airheads. They were a LOT cheaper than the other sets available, but didn't come with rubbers. You're on your own there.
    #71
  12. blaine.hale

    blaine.hale Long timer

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    If you ever stumble on that Amazon link again, I'd super appreciate a linky.

    Sounds like there is zero point in buying a $400+ kit. Just buy 2 pre-jetted Mikunis and pick up the cables Jenna was talking about. My stock rubbers should work with mounting them up?

    edit: this might be it. http://www.amazon.com/mikuni-34mm-c...TF8&qid=1363272849&sr=8-1&keywords=bmw+mikuni

    Looks like the same guy on this ebay set:
    http://www.ebay.com/itm/New-Mikuni-...Parts_Accessories&hash=item4d02188ac3&vxp=mtr
    #72
  13. Airhead Wrangler

    Airhead Wrangler Long timer

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    Yep, that's the guy. Looks like prices have gone up a bit though. Still the carbs prejetted from Sudco will run you about $150 a piece if I remember right, so with just the carbs you'd already be at $300. For $12 more this guy throws in the cables too (which aren't the greatest quality to be honest, but good enough). As for rubbers, your stock ones will work fine for the connection on the head, but you'll need to come up with something of your own for the connection on the airbox side.
    #73
  14. Beater

    Beater The Bavarian Butcher

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    Rubbers can be found pretty cheaply at an Autozone. Measure what you need and then go to their assortment of radiator hoses. You can also do what I did (and I really like the result) is cut a long piece of rubber out of an old tire tube, and wrap the intersection between the carb and the BMW tube. You can pipe clamp the result, and it winds up being very water tight. My cylinders were under water for at least two minutes, and I was able to crank immediately once out.

    I bought my first set from Rocky Point ... and the second set I got in a box of parts from a yardsale. Either way, I do have a few extra jets around ...

    PS - In my opinion I would get the 32's for the R90. The 32's on the Dobber make the engine come alive. I had 34's on Greta ('78 R100) but I think I'me getting better performance out of the 32's on The Dobber.

    #74
  15. blaine.hale

    blaine.hale Long timer

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    That brings up a good thought. Am I lazy enough to buy the pre-jetted 34 kit from this Amazon purchase or should hunt down some 32mm kit somewhere. Do you think it would be a big noticeable difference on the r90? I've seen a lot of people run the 34's on r75s.
    #75
  16. Beater

    Beater The Bavarian Butcher

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    I think you can make any carb work with enough fanagling. But here is my thoughts ... Think extremes.

    A HUGE carb on a small piston. At idle you can make it run perfectly. Once you turn the throttle, you almost immediately move completely through the sweet spot mix of gas/air, and now you're going to be giving way to much of both to the piston.

    A tiny carb on a HUGE piston. At idle the piston is not getting enough. As you give it throttle you move toward the sweet spot for idleing, and little more. You never even reach the sweet spot for acceleration / performance.

    Lesson: You need to have the carb and piston balanced. Seems logical, right? Now where is it? You will get MANY people telling you it's from 32 to 40mm. Bing, Mikuni, Delorto ... Jet sizes, idle, main, needle ... the skys the limit. Seems very daunting. Don't let it get to you. Ask yourself this question:

    1. What do I want out of the engine? Performance, Racing, Reliability, Gas milage? What?

    For performance top end, or low grunt? Racing distance or sprint? Reliability?

    I have a R100 engine that has huge low end. Mikuni 32's, 18" rear wheel, 37/11 drive. I had an R100 that had a better top end, but the balance of the engine wasn't as good ... 32/11 final drive, 18" rear wheel, and Mikuni 34's. For milage obviously a miserly approach is best ... but where's the fun in that?

    For lower end city riding, I would go with the 32's. For top end freeway I would go with the 34's or 36's. But in the big picture, I really don't think it matters. We're talking about smaller differences between incredibly variable attributes. Why, the whole formula goes out the window if you go from sea level into the mountains.

    For me, the 34's are a bit more rare in the world of motorcycles. The 32's were on MANY of the Japanese bikes, therefore you can get cheaper. WFO on the Dobber will lift the front wheel and have you praying for a better grip on the handlbars. I can cruise at 80mph ... and there is plenty more umph there ... but that's enough for me.

    In any case ... get what you want, and we'll titrate it work great. Think of it this way. BMW put the 32's stock on R75s through R100's. Not that they did everything right, they were just able to titrate the jets to make it work well. We can do the same with yours.

    #76
  17. Uncle Pollo

    Uncle Pollo Long timer

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    OR LEAN

    mine does that when i jet it too lean
    #77
  18. Uncle Pollo

    Uncle Pollo Long timer

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    cycle gear will order anything or might have it in stock

    jets are us is the best bet
    #78
  19. blaine.hale

    blaine.hale Long timer

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    Just asked Bill with Rocky Point about a jetting for a 34mm VM on an r90:

    Slide: #2.5, #3 may be OK
    Needle: 6DH3
    Main: 210
    Needle jet: 159 P-0
    Air jet: 2.0

    I told him I'm running hoske pipes with a little more flow than stock..so he may have adapted those jettings for that factor.
    #79
  20. Kt-88

    Kt-88 I like everything.

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    I may go back up on main jet size. Raising the needle actually helped.
    #80