Help carb/head combination

Discussion in 'Heads and Cylinders' started by Miguel P, Apr 4, 2018.

  1. Miguel P

    Miguel P New Member

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    Hoping for some advice on head/carb combination

    Current setup:
    26" wheel
    36T sprocket
    49cc
    Stock slant head with 2 gaskets from soda can
    SKF main bearings
    Stihl top needle bearing
    RSE reed valve
    Banana expansion
    w/ stock exhaust's whole header (~20cm)
    Custom CDI (kx/jag/ivanh/rohmell...)
    CR80 coil (NGK non-resistor boot)
    Offset intake 32mm
    NT carb 80 jet
    Cone air filter
    Running NGK B7HS sparkplug

    I'm getting 41mph maximum @ ~7000rpm
    but only wish to cruise at like 30 flat. climb maybe 20 (which IS its current state).
    Also, it starts and idles no problem

    Intake port bored only at the entrance so that the reeds open freely (actual port timing is stock and so is exhaust's and transfers. No boost port)

    My only issue is temperature. With a b7hs I'm getting around 370 degrees Fahrenheit. With b6hs was in the 400's. I'm getting a B8HS tomorrow and we'll see how it goes.. Either way plugs don't do miracles so it's high time I get a bigger head for cooling. And I'm thinking of a Puch head (https://www.treatland.tv/Puch-50cc-Hi-compression-head-p/puch-hi-comp-head-50cc.htm)?

    So then my big question mark is I feel like I should go for bigger carb. I'm already at an 80 jet on the NT, puch head should be cooler and allow me to up compression a bit so it seems I should go bigger carb.. am I right. Still, I am unsure because of having reeds. So, in a scenario where bigger carb is beneficial would that imply bigger reed size also?? In other words, is fuel delivery limited by reed size?

    If not, What size should I go? As I have read, reed-valved needs smaller carb compared to piston-ported and too big a carb will lead to low rpm issues. So I'm thinking a modest increase from 14mm of the stock NT to maybe 16mm?
    I'm considering this guy pz16 (https://m.ebay.com/itm/KEIHIN-Japan...339593?hash=item1c9f28dcc9:g:qMQAAOSw05taZ2bN)

    But then the most important thing, which range of jets to get?? Specially for the pilot jets which I have zero experience with. Anyone run carbs with pilot jets ob these engines?
     
  2. Tony01

    Tony01 Active Member

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    so it already has the performance you want but you wanna fix it till it doesnt? what was the question again?
     
  3. Dan

    Dan Staff
    Staff Member

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    LoL, Tony. Have we met? Is kinda our thing to tweak beyond reason. Think the tweaking is part of the allure. Squeezing every last bit out of 'em. I just bought a computer to talk to my cars computer so I can find out why she's only getting 42.6 MPGs. Think I'd be happy, NOoooo. snork.

    Miguel, quick question and am probably misreading. But if the goal is to lower internal heat. Wouldn't a high compression head be counter to that? Or am in fact misunderstanding.

    Reading your post, you seem to be really well versed and am just asking.

    Dig the head you posted. Gonna really add a techy, power sorta look.

    Can ya post how well it cools for ya with them big 'ol fins but higher compresion? Really curious.

    Ride safe!
     
  4. xseler

    xseler Well-Known Member

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    That Puch head is what Mapbike had on his bikes. He said that was the only one he'd run after using it.
     
    Dan likes this.
  5. Dan

    Dan Staff
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    Thats cool, X. I personally always consider Map's suggestions and thoughts as having great weight.
    Really knowledgeable well versed and helpful folk.
     
  6. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

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    The Puch head is the only choice for a 40 mm piston 48cc.
    Fred heads and other heads are only made for 47 mm 66cc and 69cc motors.
    Do you have a hole in your piston for the reed valve to work properly?
     
  7. Tony01

    Tony01 Active Member

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    IMO there is only so far you wanna go with any cheap chinese product. better to get it running how you want and not mess with it, then build a new bike with a much better base engine. Like a small karting motor or goped motor.
     
  8. CrazyDan

    CrazyDan Member

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