very bad gas mileage.

Discussion in 'Motorized Bicycle General Discussion' started by LongboardMalinois, Jul 29, 2015.

  1. LongboardMalinois

    LongboardMalinois New Member

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    I have had my bike going for a week or so now, and the whole time i have been noticing terrible gas mileage. Today i put about 1/5th of a tank of gas in, and i went on about a mile or less long ride, and when i returned home and checked the gas level the tank was dry. So i am getting 10-15 mpg. Is this a problem with my carb? I have a 66cc china girl engine and the so called "Speed" carb which had the ugly red plastic airbox on it when it was delivered, although i have since removed the plastic piece.
    Any input would be greatly appreciated. Thanks!
     
  2. crassius

    crassius Well-Known Member

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    some of these motors are horrible till they're run in a bit - also, if you seem to be 4-stroking a lot, you may want to drop your needle down a notch to make it leaner

    note: it will get leaner as it runs in, so watch your spark plug to see if you need to move the needle back up later
     
  3. Legwon

    Legwon New Member

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    Well, a couple things come to mind, as I also run that carb.
    Are your wheel bearings free?? Bad bearings no matter where they are will cause your engine to work harder for the same speed achieved by good bearings, hence using more gas.
    Does your bike pedal easily when clutch pulled? Possible engine bad engine bearings.
    Have you tuned the carb? The carbs come stock with a setting on the needle in the middle.
    What speeds are you doing?? Run to fast or too slow, your using more gas than you need to. Each engine has its own sweet spot according to how it's set up.
    Hills?? Use more gas goin up hills.
    Only a mile?? Engine doesn't really warm up till 4-5 mile mark, then fuel savings kick in.
     
  4. LongboardMalinois

    LongboardMalinois New Member

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    Damn, i hope i don't need new engine bearings! I am 4 stroking a lot and the spark plug is completely black and covered with oil when i remove it, so i suppose i do need to make it a little leaner. My bike pedals quite easily with the clutch pulled in. My cruising speed is 15-17mph, i am keeping it a little slow for break in. some hills are around, but i help it up the hills with the pedals. Which way do i move the clip on the carb needle to get it leaner? Also, even if some engines are horrible with mileage are they as bad as 10-15mpg?
     
  5. Greg58

    Greg58 Well-Known Member

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    Moving the clip up lowers the needle to lean the mixture, while you are working on the carb check the jet to make sure its tight. I've had the main jet get loose on two different type carbs.
     
  6. Slogger

    Slogger Member

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    Mine wasn't quite that bad but it got lousy milage the first tank. Blubbering rich, rings not seated, low power so the throttle is open more all adds up.
    I was also told to leave the jetting stock for a while but it ran so badly I changed the main and dropped the needle by the second tank.
    Let your bike warm up for a couple minutes before you ride, it seems to help the milage quite a bit. When cold, it sucks some gas.
    Now it will run in the mid 20s at half throttle and gets way over a hundred mpg riding easy.
     
  7. Davezilla

    Davezilla New Member

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    Mine got that kind of milage before it was fully broken in as well, and another thing to consider is the advertised 100 to 130mpg is possible but not at full throttle where the engine can consume 2 to 3 times the amount of fuel it does while cruising, add in overly rich jetting from the factory and any extra load like hill climbing, fast take offs, or a heavy rider, or carrying extra stuff etc, it all adds up and takes away from the gas milage.

    The best fuel milage will be experienced with the highest manifold vacuum and the lowest engine rpm for a given speed. Of course, trying to read vacuum on a 2 stroke single cylinder is near impossible without some kind of a restrictor in the line and I don't know of anyone who uses a vacuum gauge on their bikes, but high vacuum can be translated to light engine load, so basically, the lower the engine load and rpm at cruising speed, the better the fuel milage will be.

    Things like going fast all the time, under or over gearing, riding in hilly areas, heavy riders/bikes, underinflated tires, dragging brakes, bent rims, etc, etc as well as running in a new engine can add up to some really poor gas milage.
    Cruising at about 50 to 75% of the bike's top speed with as little load on the engine as possible is what's going to get you closer to those advertised gas milages, providing you're on flat ground, not going against the wind, and your bike is straight and true with properly inflated tires and nothing putting a drag on the bike.
     
  8. LongboardMalinois

    LongboardMalinois New Member

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    Ok, i will try moving the clip on the carb needle up a notch. The engine is carrying a very light load since i am a smallish person and it is on a light aluminum frame bike.
     
  9. Davezilla

    Davezilla New Member

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    I agree about trying the next clip position if the poor milage is happening during normal cruising and the spark plug is black or really dark when checked.
     
  10. LongboardMalinois

    LongboardMalinois New Member

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    So i took apart my carb to change the setting, and the clip on the needle was caught halfway on top of and halfway under the washer with a cut in it (not sure what that washer is called) so i got it uncaught and all the way under the washer. Huge power increase, no more 4 stroking and less smoke! But now i'm worried it could be too lean. I cleaned the spark plug and went for a ride around the block, looked at the plug and saw no change in color. How far do i need to ride before check my plug?
     
  11. crassius

    crassius Well-Known Member

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    it may take a fair amount of time if the plug is thickly coated with oil - glad you got it running better
     
  12. 2door

    2door Moderator
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    Don't 'baby' the engine so much. It needs some WOT, wide open throttle, time during break in. Don't abuse the engine but it wants/needs some hard running during this initial period.

    You'll probably start seeing a change in plug color after another few miles or a couple of gallons of fuel.

    What fuel/oil ratio are you running. If you're going by the kit instructions that say 16:1 that has been determined to be too much oil. Drop your ratio down to 24 or even 32:1. I think you'll see a difference in how things perform.

    Tom
     
  13. tooljunkie

    tooljunkie Member

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    The "fast guys" i used to know back in my snowmobiling days would start with a new set of plugs and go drive hard for a mile , come in hard and shut it down without letting it idle. Called it reading the plugs.
    If its not four stroking or falling on its face at wot, you should be close.
     
  14. LongboardMalinois

    LongboardMalinois New Member

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    I am using the 16:1 ratio right now, but i will take it to 24:1 on on my next gallon of gas. And i admit i do baby the engine quite a lot, and i have only gone full throttle for a few seconds at a time, but the main reason for that is i am scared to go that fast, the bike is hitting 35mph at half throttle, but for the brief seconds that i do go full it is not 4 stroking, and it has a scary amount of power. Enough power to easily do a wheelie when i'm already going 20mph. I guess i will find a road without too many cars and give it WOT for a little while. Also, what is the right plug color to look for? Thanks to everyone on the forum for answering all my questions, and hopefully i will be able to help someone else fix their bike problems at some point.
     
  15. crassius

    crassius Well-Known Member

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    many folks here would go to 32:1
     
  16. LongboardMalinois

    LongboardMalinois New Member

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    Like i said, i baby the engine a lot.
     
  17. LongboardMalinois

    LongboardMalinois New Member

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    And i should mention that the bad gas mileage is much improved.
     
  18. xseler

    xseler Well-Known Member

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    I honestly don't remember ever checking the fuel mileage on mine. I'm more into the 'smiles' per gallon mode.

    BTW, I used 32:1 for break-in and have used 50:1 (Echo oil) for the past 2 1/2 years. When the tank is low, I add more fuel mix.
     
  19. tooljunkie

    tooljunkie Member

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    That seems pretty quick. If my engine run that good i would not be upset with fuel mileage. Just carry a spare couple quarts.
    Plug color-dark brown is the typical color to look for. Not black.
     
    #19 tooljunkie, Jul 30, 2015
    Last edited: Jul 30, 2015
  20. 2door

    2door Moderator
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    "35 at half throttle". Just curious as to how you're measuring your speed. As most will tell you that is an impressive number for a new, stock engine running on 16:1.

    If it ain't broke, don't fix it.

    Tom
     

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