Still getting really bad gas mileage.

Discussion in 'Motorized Bicycle General Discussion' started by LongboardMalinois, Aug 30, 2015.

  1. LongboardMalinois

    LongboardMalinois New Member

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    My bike is getting quite bad gas mileage, by my estimate 27-30 mpg. It is very close to broken in and i recently changed to a 30:1 fuel mix, and moved the clip on the carb needle to the second position from the top. I think that it has been getting bad mileage from the get go, but until recently i have not been going on longer rides, so i didn't notice it as much, and what i did notice i just attributed to breaking in and overly rich carb settings. It is also not particularly fast, and it still 4 strokes a little even after changing the carb setting. So i am wondering if i might need to look at the jet and see if something is wrong there. All the bearings are OK on the whole bike and engine, and it rolls almost as easily as a regular bike.
    Oh yeah, and i should mention that it is a 66cc china girl with a "Speed" carb.
     
  2. Agreen

    Agreen Member

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    Do a plug chop!

    When does it 4 stroke? Partial throttle or full throttle?

    Did you change the spark plug to the NGK yet?

    Also, are you shutting the fuel off when you aren't riding it? I didn't do that on one bike. I also parked it over grass. The tank would drip dry in a day or 2 and leave me wondering why I got such bad mileage. I parked it on pavement once and saw the drips... suddenly 2+2 equaled 4 and I felt like an idiot.
     
  3. LongboardMalinois

    LongboardMalinois New Member

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    It 4 strokes just a bit around 1/3 throttle when it is not yet heated up fully, and always at full throttle, no matter what temp it is at. It runs great when under heavy load, such as fast acceleration, steep hills and burnouts. And i am still using the kit plug, but i will be getting a few NGK ones today. I do shut off the fuel valve when i park, and it is stored over pavement, so even if it was dripping i would see it.
     
    #3 LongboardMalinois, Aug 30, 2015
    Last edited: Aug 30, 2015
  4. Agreen

    Agreen Member

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    Got it!

    If it's 4 stroking at wot, the jet is too big and needs to be soldered and redrilled.

    2door has a really good video on how to do that.

    And change that crappy spark plug!
     
  5. LongboardMalinois

    LongboardMalinois New Member

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    Is there a smaller jet that i can just buy? I don't trust myself not to screw it up if i try soldering it. Also, where do i find 2door's video?
     
    #5 LongboardMalinois, Aug 30, 2015
    Last edited: Aug 30, 2015
  6. 2door

    2door Moderator
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  7. Agreen

    Agreen Member

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    Buying jets is somewhat a crapshoot. You would need to buy a large selection of them because the majority of manufacturers dont follow a set standard. It's far more accurate to solder and drill.

    However, i remember seeing the jets on gasbike's website.

    FYI:
    I soldered mine with a cheap plumber's torch and regular rosin core electrical solder. It doesnt really matter what solder you use. The key is to get it clean, and apply solder to the hot part, not in the flame.
     
  8. LongboardMalinois

    LongboardMalinois New Member

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    Thanks for the video! Very helpful. What jet size would you suggest for someone who lives at around 100 feet above sea level? By the way, i liked the video and subscribed to your channel. And a strange thing happened today while i was riding. The engine started sputtering and popping, and did so for about a minute, and then started running smoother than i have ever had it run, so i gave it some throttle and wow, it must have gone 0 to 30 in about 10 seconds! More power than ever before, but still 4 stroking at WOT. Funny thing is i read someone else's comment on the forum today describing the same thing happening! Agreen, i will check gasbike. Thanks!
     
  9. LongboardMalinois

    LongboardMalinois New Member

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    So see what you think of this, i just removed my spark plug, which is the stock kit one that i have been using the whole time that i have had the bike. The porcelain insulator in the middle is very gray colored, which i would think indicates very lean running, but it 4 strokes at wot. Now this wasn't a proper plug chop, this was just after riding for a while, with plenty of idling and stops, and also quite a lot of WOT. What does this mean? Should i adjust the carb clip down a notch?
     
  10. Agreen

    Agreen Member

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    http://www.gasbike.net/carburetor-jet-kit-4121-prd1.html?disableMobileView=1

    Just beware, gasbike is somewhat hit and miss when it comes to getting you your parts. I got my frame no problem, so i cant talk bad, but others will tell you different.

    You cant just make a blanket statement about what jet works best at a certain altitude. The one that works best for you may not work so well for your neighbor with the same kit.
     
  11. SoldierBoy

    SoldierBoy New Member

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    Sounds like its carbon build up in the motor to me .If it does happen to be a older motor check the inside of the motor IE the head and piston top for carbon build up . Carbon can suck up gas and cause pre ignition
     
    #11 SoldierBoy, Aug 31, 2015
    Last edited: Aug 31, 2015
  12. Davezilla

    Davezilla New Member

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    If the spark plug is showing lean or normal it could be a miss at full throttle due to the poor quality stock plug.
    I would recommend switching to a good plug and setting the gap to .024 to .026" and see how it runs before putting a leaner jet in the carb.
     
  13. Agreen

    Agreen Member

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    Or carbon is giving you a "glow head" effect. Some RC airplane engines use a glow head, which is essentially a heated wire that glows white hot when a current is passed through it, then once the engine is running it continues to glow without electricity because the combustion makes it hot. Carbon hot spots can do that. Usually, they cause pre-ignition. That's really bad. And the carbon buildup can come from many sources, but mainly too much oil mix or an insufficient spark.
     
  14. SoldierBoy

    SoldierBoy New Member

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    Sea foam is the cure to it run the sucker on high rev and dribble it in .Dont hydro lock it though
     
  15. Agreen

    Agreen Member

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  16. LongboardMalinois

    LongboardMalinois New Member

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    Yes, the spark pug shows very lean, the porcelain insulator is grayish colored and the metal around it is dark brown, but i think that this is just from use. Should i lower the clip on the carb needle a notch? Right now i have it at the second notch from the top.
     
  17. Agreen

    Agreen Member

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    Can't tell you anything until you change the plug and then read it.
     
  18. Dave31

    Dave31 Moderator
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    Is that per tank or per gallon? A lot of past customers would tell me "I am only getting 30mpg" Only to find out they meant per tank.

    That is pretty close to what I get per tank. That is why on my long rides I always add a spare tank. Around 60-65 is what I get for a gallon.
     
  19. LongboardMalinois

    LongboardMalinois New Member

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    I do mean per gallon. I am getting between 10 and 17 miles per tank.
     
  20. crassius

    crassius Well-Known Member

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    2-strokes are peaky - I often notice that I'm holding throttle way too far open for the speed I'm going and can roll it back quite a bit and still go that same speed

    however, my best mileage happens at about 25mph on level ground - I get way over 100mpg when I can do that
     

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