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Help MC22 carbs on MC 19 - carb tuning

Discussion in 'Honda 250cc In-line 4's' started by Jacob Lowe, May 3, 2018.

  1. Jacob Lowe

    Jacob Lowe Active Member

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    Hey guy iv got some late model vp carbs off a mc 22 on my mc 19 and they seem to perform much better up in the revs im currently running stock jets and needle shim. What sizes jets are people running using these carbs and a good flowing aftermarket exhaust? Im having trouble with a lower rpm cruising under load bog but idles and preforms well from 7 - 18k I brought a keystar carb kit and the new needles included were about 1mm longer and the taper appeared different my oringinal needles are “J4GA” keystar needles “ D564” has anyone noticed this before? The carbs have been soaked and one slide diaphragm was replaced.
     
  2. jmw76

    jmw76 Well-Known Member

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    Hi Jacob,

    I have not swapped carbs around between bike models, but have struggled for a while to get my little 92 MC22 track bike to run correctly for some time.
    I played around with jets for a while. I run a number of configurations from 105 through to 112 and different washer combinations under the jets. I just could not get it sorted. It was bogging up plugs and ran out of puff at about 17k rpm.
    I finally purchased a cheap carb rebuild kit from ebay ($33). This resolved the majority of issues that I had. I kept the 108 jets that I preferred however.
    I did notice that the needles were a little different, but so were the jet tubes that were supplied. I just figured that they were a matched pair. Anyway, they seem to work well. I have installed them with 1 standard washer under the needles. The idle mixture screw is 2 turns out. The motor runs fairly cleaning from idle all the way up.
    I have yet to take to the track again, but my quick test ride indicated a good improvement.

    I purchased some new vacuum diaphrams but have not attempted to fit these yet. The looked like they might be troublesome to install and since the others were not that bad, I just left them alone. Is there a special technique to fit new diaphrams?

    Cheers

    Peter.
     
  3. Jacob Lowe

    Jacob Lowe Active Member

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    Hey Pete I struggled to find information on fitting them myself . The Chinese diaphragms are hit and miss make sure you give them a tug right around to check you haven’t got a faulty one some just ripp apart. I used an old airbox and holesawd the approx size to fit the top cap as the original needs to be ground off. I then used a good quality super glue sparingly, being sure to align the diaphragm ear in the right spot. Seems to do the job i only did the one damaged slide because i wasnt sure how it would go. Be careful putting them back in they seem slightly smaller then the originals and are easily pinched by the lids.
     
  4. Wozza

    Wozza Active Member

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  5. kiffsta

    kiffsta Senior Member

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    the MC19 and MC22 engines are MC14e's, they are similar but with subtle differences in the heads, cams etc , maybe start with stock jets then work your way from there, 102/105 mains on the L and N models, I run 4x 108's on my racebike.

    did you get VP20A or B carbs ? as the stock jetting on the VP20B carbs are 110/112
     
  6. Jacob Lowe

    Jacob Lowe Active Member

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    The carbs I brought had 110 112 in them so I gathered they were B carbs seems too run good mid and highrevs iv got some smaller mains to try And also just got an AFR meter set up to try narrow down the issues im having during cruising
     
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  7. jmw76

    jmw76 Well-Known Member

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    Hi Guys,
    A bit of an update on my recent experience after putting the rebuild kit in my carbs.
    Ran at Broadford in June. All ran much better than previous with 4 x 108 jets, but lacking at the top end. Can not get any real power above 17k. Played with the throttle a little on the last run to try and determine if mixture needs adjusting. Seemed to pull a bit harder as I backed off. Suspect I need to go down a jet size. Will try 4 x 105 next time.
    Peter.
     
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  8. Jacob Lowe

    Jacob Lowe Active Member

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    I ended up running 98 and 100 jets and have yeilded best results so far still seems rich through the low to mid rpm range but I Think with out access to different needles or adjustable float height it's about as good as it will be.
     
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  9. jmw76

    jmw76 Well-Known Member

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    Hi Jacob, how have you determined that it is rich? Have you managed to get the top end running well?
    Have you tried adjusting the needle height with washers? This might help a bit with your mid range issues.
    The rebuild kit that I purchased out of china was very economical. https://www.aliexpress.com/item/bra...230.html?spm=a2g0s.9042311.0.0.105c4c4dLs9o74
    I will post my experiences with changing the jets after my next track day.
     
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  10. Jacob Lowe

    Jacob Lowe Active Member

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    I fitted a wide band, and where the motor feels flat the Meter reads bout 10:1 but pulls out of it. I've tried a few different needle heights Its currently standard one washer I'd actually like to try different needle profiles. My previous major rich issues were caused by needle holder wear so as the needles had worn slight grooves and no longer sealing as the are surpose too (kinda). So Another set of carbs and down a few jet sizes has helped allot. I'm happy enough with it as is for now as Iv probably had the carbs out 100 times (no joke) to get to this level and this is the 4th set of carbs haha
     
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  11. Jacob Lowe

    Jacob Lowe Active Member

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    Also have to remember that the mc 19 I imagine flows a bit better across the head and maybe a slightly larger cam then the later 22's which I imagine is why the 19 needs to be jetted down even with an open exhaust fitted when using mc 22 carbs as the jets are receiving a slightly stronger pulse and drawing more fuel then the same sized jet on the lesser flowing motor. Thats my theory anyway.
     
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  12. jmw76

    jmw76 Well-Known Member

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    Taking the carbs off and on is a bit of a bugger. I can not possibly imagine how you could tolerate doing this 100 times. It would be really nice if you could get access to the critical bits without removing as much gear. The problem with tiny complex bikes I guess.
    You have gone to more trouble than most by fitting and EGO sensor. I really can not be bothered. The suck it and see approach is working currently for me.
    My track bike is an early mc22, so has the de-restricted 45bhp powerplant (mc19).
    I am also running 1 washer. Hopefully dropping the jet size further will liven up my top end.
    Cheers
     
  13. Jacob Lowe

    Jacob Lowe Active Member

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    Have you done the basic service things balance carbs+ valve clearnces and a comp/leak down test after verifying that you have ample clearance.?
     
  14. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    What Jacob says is spot on. You can't compare jet sizes across different bikes and models. Most owners always try bigger jets when the correct way is to start rich and keep going down in size until it falters then go back up one. Always worked for me.
     
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  15. jmw76

    jmw76 Well-Known Member

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    Nup.
    Have not check valve clearances or compression test at this point. Have balanced carbs the old fashioned way, by ear and length of tube. idles quite well. I am not one that believes balancing fixes all issues. It mainly only solves idle issues. I have other multicarb high performance engines that all run just fine using either the tube or bench balancing techniques. Engine sounds sweat (except at really high revs). I plan to check valve clearances soon, but concerned this means engine out to do the job.
     
  16. jmw76

    jmw76 Well-Known Member

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    Planing on being back a Broadford on 18/8. Will report on setup after.
     
  17. jmw76

    jmw76 Well-Known Member

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    Changed back to standard jet sizes.
     
  18. Jacob Lowe

    Jacob Lowe Active Member

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    Just an update i ended up running 4x105 main jets standard pilots with mc22 carbs airbox and 4 short velocity stacks with an open exhaust system straight through muffler. This yeilded the best results on my machine.
     
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  19. jmw76

    jmw76 Well-Known Member

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    I am glad that works for you @Jacob Lowe . I finally resorted to putting my track bike on a friends dyno to sort it out.
    The final jet size I ended up with was 95 on all carbs. Running a straight through muffler and foam air filter. Otherwise everything thing else is pretty much stock. Measured 42bhp at the wheel.
     
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