Carb Runs fine with no air filter???

Discussion in 'General Tuning' started by bikerbeynard, Jan 5, 2012.

  1. bikerbeynard

    bikerbeynard Luke

    Messages:
    164
    Rides:
    gpr 125 ,mbk rocket,
    Just fitted my new dellorto 17.5 carm to my mbk rocket 70's with 110 jet with the standard airbox it doesnt like to move anywhere full throttle. But when i remove the airbox the bike runs just fine.

    Do i need to go down to like 100 main jet or do i need to get more air into the standard airbox I.E. Remove snorkel,drill holes or buy sports filter

    I know 110 n 100 jets sound big for a 17.5 on 70cc but the bike comes standard with a 93
    shall i try this one let me know

    Cheers dudes!!
     
  2. murerg

    murerg MBK Hero!!!

    Messages:
    744
    Need a bigger jet I would think. Should be able to open full throttle.

    Do a sparkplug test... usual stuff for jetting.

    Note: Id be interested to know what set-up you have :)
     
  3. bikerbeynard

    bikerbeynard Luke

    Messages:
    164
    Rides:
    gpr 125 ,mbk rocket,
    but if the bike runs bang on with no filter surely it means the bike needs more air
    its in my signature apart from i removed 21mm carb for 17.5 one
     
  4. bikerbeynard

    bikerbeynard Luke

    Messages:
    164
    Rides:
    gpr 125 ,mbk rocket,
    no i need to do anyhting to the needle or main jet?
     
  5. u33db

    u33db Member

    Messages:
    358
    Rides:
    Several Bikes
    The bike may come with a 93 main as standard but thats on a 13mm carb.

    With a 17.5 you'll want something smaller if using the airbox.

    My engine is the same as yours (also with 70cc) and when i fitted a 17.5 it was running an 85 main jet with the airbox.

    I didn't set the bike up in any detail as i removed the 17.5 shortly after but with an 85 the bike would at least ride about town happily enough so try something around that size.

    110 is massive though - i use a 110 in a 22mm carb with open cone and when i get round to setting the bike up properly i'd likely be going down several sizes...

    With the airbox you'll definately want under 100 for the main jet, even with 70cc and exhaust.

    If you don't have smaller jets then 110 in a 17.5 may run well enough with an open cone filter if you have one lying about?
     
  6. murerg

    murerg MBK Hero!!!

    Messages:
    744
    I would still recommend a spark plug test anyway :p That would tell hewlp you figure out what you need to do.

    You dont need to do anything to the needle by the way. Main jet is done before everything else.

    Note: Never even noticed your sig! :D Nice wee setup :)
     
  7. Jonnymarrw00t

    Jonnymarrw00t Moderator Staff Member

    Messages:
    3,243
    Rides:
    Piaggio Zip 05 plate
    You'll want a 80-90 jet.
     
  8. bikerbeynard

    bikerbeynard Luke

    Messages:
    164
    Rides:
    gpr 125 ,mbk rocket,
    cool im gunna set up my ped this week..thanks peeps
     
  9. MadHead69

    MadHead69 New Member

    Messages:
    11
    I no this is a old post but I’m having a problem with my speedy I’ve fitted a cast iron metra 70cc kit and it seams to run better with out the air box the carb is the standard 12.5 gurtner carb and was fitted with a 62 main jet and ran great when standard but now it as a 70 kit I up jetted to a 72 but I will only run with the air box off is the main jet to small or to big
     

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