Phbg carb tuning help

Discussion in 'Scooter Tuning' started by Trigen, Aug 3, 2017.

  1. Trigen

    Trigen New Member

    Messages:
    4
    Hi!

    I got a 19mm PHBG carb that i got some issue with.

    When i drive it and cut the throttle it will start to bog and then shoot off again. i suspect its the idle screw or jet thats wrong. It gets better when i lean out the idle (screw it in) but then the bike will stall very easy when it drops to idle and i need to keep the idle above 1150-1200 rpm. The screw is about 1.8 turns out and i need to go in to 1.5ish for the problem to be almost gone. Ive gone a bit up and down on the idle jets but cant quite recall whats in there now as i havent looked at it in a while. Im having a hard time tuning it tbh and im not 100% sure when its 4 stroking or not but i try to get as even running as possible. It just feels mostly the same.

    For the needles ive gone from, i think its a w6 in there as standard and all the way up to a w10 and notch 2 from the bottom and still have the issue. Im going back to a w9 as the stock is definitively wrong and sputters a lot.

    Anyone got some experience with this?
     
  2. Tamiyacowboy

    Tamiyacowboy Pippa's Owner

    Messages:
    1,850
    Rides:
    Piaggio Skipper
    0 to 1/4 throttle is idle and mixture setting . 1/4 to 3/4 is needle

    if this is happening after 1/4 and before fully open on the throttle im gonna say its more a needle setting. thry bumping the needle to 3rd from bottom , this is gonna lean out the mid range throttle area so keep an eye on it . that may just help .

    moving the notrching down on the needle richens the flow , so if we go up a notch is gonna lean out the mid end a bit . see how that goes .

    what bike are we working with and what was the original jet size and the jet size after upjetting ?
     
  3. Trigen

    Trigen New Member

    Messages:
    4
    The bike is a TGB bullet rs 50 with this muffler http://www.tecnigas.com/o/model.php?codi=17&cat=2&idioma=en and a 19mm phbg carb

    It had a 15mm carb org. on the 19mm it was 75 on the main jet but upjetted to 80. running it at 75-78 will give some engine ping and metallic noise.

    Its generally from full throttle and then cutting it. The faster i cut it the more it will suck in extra gas loose power and then shoot off. It also happens from about 3/4 id say too. I can try to lean out the needle a little bit more and see how that goes but it felt the same as a tad richer needle which is why im leaning more to the idle since it affects the whole range if i remember correctly. Unsure about this though so ill move the needle and see.
     
  4. Trigen

    Trigen New Member

    Messages:
    4
    Actually! It looks like you may be right here. Going up a notch did make it a whole lot better and i got much more power. Before if i held it in a spesific spot around 1.5/4 i could pass my limiter at 9k and go to 10k rpm. Now i have that power until 3.4/4 or right before full. Ive been quite nerouse about the needle since ive gone from about a W6 all the way to a W10. IT still feels slightly off from 2/4 to 1/4 like it drops a tiny bit in power and then gains a little before going down again but i guess some slight tuning of the idle will fix that. Thanks for the tip! Ill keep a close eye on it now though
     
  5. Tamiyacowboy

    Tamiyacowboy Pippa's Owner

    Messages:
    1,850
    Rides:
    Piaggio Skipper
    aye keep a good eye on that temp gauge any build up beyond normal chop the throttle and nurse it back home gentle , shove a new sparkplug in do a good couple high end top speed runs, then chop the plug out to see the current tune state.

    white'ish plug tip and ring = bit to lean
    blackened plug tip and ring = way to rich
    chocolate brown tip and ring = perfect ratio on fuel and air clean burning to
     
  6. Trigen

    Trigen New Member

    Messages:
    4
    Gonna do a few plug chops over the weekend. For now it runs more as it should. Runs bad without choke for the first few minutes. runs perfect with. No worse or better when choke is on warm. And well the performance is miles better. Got it set for more acceleration and a top speed of 72 kmh GPS - 75 to 78 if i take it to 9500. Forgot to mention it got an Athena 70CC racing kit so its a fun little scooter that i enjoy in the turns

    It should not start so easily without choke though and it does so im fairly sure i need to lean it there but at least it runs better overall now so its not a huge issue
     
    Last edited: Aug 3, 2017
  7. Tamiyacowboy

    Tamiyacowboy Pippa's Owner

    Messages:
    1,850
    Rides:
    Piaggio Skipper
    glad that needle adjustment has been some use to you trigen and your scooter now acts like it is a 70 kitted beast and not a standard purring kitten .

    yes keep an eye on temps, do a couple plug chops just go easy for a while and see how she fairs up with that needle setting tweek and that new needle .
     

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