Bike too slow

Discussion in '2-Stroke Engines' started by Mp2003, Jul 11, 2016.

  1. Mp2003

    Mp2003 New Member

    About a week ago I bought a 2-stroke 80/66cc bike kit. I installed it and after startup problems at first I managed to get it running smoothly, the only problem is, it is way too slow. It struggles to stay at 20mph with the throttle wide open. I checked the carb and the throttle runs fine, so it's not that. I'm using 20:1 oil to fuel on a 26" mountain bike. PLEASE HELP!

  2. FurryOnTheInside

    FurryOnTheInside Active Member

    Carb adjustment obviously, but
    The entire electric system needs to be checked, fixed and improved from the keyway on the crank shaft all the way up to the plug gap. Lots of reading to do. Whole section on it. Most of the problems that come up are free or inexpensive to fix and not expensive to improve.
    The engine needs fuel, lubricant, air, carburetion, compression, spark, exhaust, cooling.
  3. Frankfort MB's

    Frankfort MB's Well-Known Member

    Your probably running too rich of a fuel air ratio..... If you pull your plug and its black on the end then your rich.
    A quick fix would be too take air filter off, but to be right you need to rejet the carb to a smaller jet.
  4. OTP

    OTP New Member

    Give it time to break in. After about 200 miles mine runs so much better. It was pretty sad at first but now its pulling me up some steep hills with no problems. I was worried at first but happy with it now.
  5. Mp2003

    Mp2003 New Member

    I really hope that's all it is.
  6. Mp2003

    Mp2003 New Member

    I'm not home now but I'll check it in about an hour when I can. Thank you for the help.
  7. Mp2003

    Mp2003 New Member

    It was black and oily and I moved the jet needle to the leanest position, still nothing changed. Also how would I go about removing the air filter and would it still run okay without it.
  8. Frankfort MB's

    Frankfort MB's Well-Known Member

    It will run ok just don't ride it too much like that because it will let dust and rocks and water in the engine.

    What it does is it lets the engine breath more (think of it like your trying to breathe with a sock in your mouth then breathing w/o it.... Big difference in air flow) when it lets more air in it will lean out the mixture.

    When you lower the needle all that does is the low to mid fuel:air mixture, the jet is full throttle adjustment
  9. Frankfort MB's

    Frankfort MB's Well-Known Member

    Your probably running a little too much oil btw.... 32:1 with full synthetic is perfect
  10. Mp2003

    Mp2003 New Member

    I already put in 16:1 oil to fuel a few hours ago. It'll be a while until it's empty but when I do fuel up again I will do it 32:1 next time. Thanks for the help.
  11. OTP

    OTP New Member

    if you go to and look on the right side, you'll see jets for these carbs are his best sellers.
  12. KCvale

    KCvale Motorized Bicycle Vendor

    Maybe it's just my location in the desert, but I have NEVER had to re-jet a carb.
  13. jaguar

    jaguar Well-Known Member

    If the plug is black then it needs a smaller main jet.
    a restrictive air filter (stock) can also cause it to run rich. I made my own out of a foam lawn mower filter.
    I cut it up and glued it together with silicone sealant. It stays together but you can't use gasoline to clean it, only soap and water.
  14. Steve Best

    Steve Best Active Member

    Don't run without a filter. Do like Jag did or get an oiled gauze filter, or even keep running the stock one. No filter will equal no cylinder very soon.

    WINDY CITY BOB likes this.
  15. Frankfort MB's

    Frankfort MB's Well-Known Member

    done it for about 150 miles but I ride on the road and nothing too bad yet. I probably shouldn't but it's fine for quick testing just don't do it in really dusty or dirty conditions

    SEGACDX Member

    Alright I've been reading these replies to your question. What will fix your problem right away is to move the spacer on the needle in the carburetor from the third from the top to the Second notch, this still make the engine run leaner and a lot better than the stock option.

    Here is a great guide on doing that:

    Do not remove your air filter that is just a stupid idea and will not help you one bit if a small rock or even some dirt particles get in there you will have a lot of unnecessary wear. Go get yourself a aftermarket air filter if you really want to replace it.

    Like someone Said run full synthetic 2 stroke oil 32:1 about 157ml per 5L, this is the ratio I have used for years and I find it works the best. Replace the stock engine bolts, sick bike parts has a kit for that but you can use 12.9 Grade steel M6 socket cap, 40mm, 25mm and 35mm to replace all the engine bolts get about 12 of each so you have extras and get some locktight red to keep them from vibrating loose this causes air leaks and loss of power, it happens super fast on these engines within a few short rides. You also get the bolt kit from Sick bike parts but it's not the strong stuff only grade 5 so your better off getting the 12.9 grade stuff from fastenal, plus it's much cheaper.

    Links to everything I mentioned.|categoryl1:"600000 Fasteners"|~ ~|categoryl2:"600039 Sockets"|~ ~|categoryl3:"600040 Socket Cap Screws"|~ ~|sattr06:^"Class 12.9"$|~|categoryl1:"600000 Fasteners"|~ ~|categoryl2:"600039 Sockets"|~ ~|categoryl3:"600040 Socket Cap Screws"|~|categoryl1:"600000 Fasteners"|~ ~|categoryl2:"600039 Sockets"|~ ~|categoryl3:"600040 Socket Cap Screws"|~

    Some good oils recommendations:

    I've been using that Lucas oil Snowmobile fully synthetic for a bit and it's killer stuff and a good price where I live, you can use it in al 2 cycle applications for air or water cooled engines.

    Grab yourself a new spark plug, NGK B6HS, BP6HS, BRP6HIX are all great options but I personally Recommend the BRP6HIX as it is an iridium plug so it will not foul easily and will last a lot longer than standard plugs.

    Consider coating your aluminum head gasket in Copper spray as gasket or Ultra copper RTV, this is a super effective way of stopping head leaks on these bikes and the RTV is good for making all kinds of gaskets.

    I hope that helps if you need anymore help feel free to ask.

    Happy Motoring!
    Last edited: Jul 16, 2016
    gary55 likes this.
  17. gary55

    gary55 Active Member

    In Prescott Az. elevation is 1 mile. I have to re- jet NT carbs. With a . delorto #68. It's a 5mm jet. If you are from 4500 to 5500 ft. in elev. this would be a good place to start. With this set up at 5200 ft. most engines like the c clip on the second notch down from the top of the throttle needle. Don't know what your elev. is, but like OTP said you can get the jets at While your there get one of their ADA racing air filters. They work great, easy to clean, last longer than your engine will "especially if you run with no filter", and hell they even look cool. You are using to much oil. 4 Ozs. full synthetic per gallon after break in. Steve is dead on no filter means no cylinder real soon. KCvale is in Phx. so if you are at or close to sea level you should be able to adjust needle settings without re-jetting.
    Last edited: Jul 16, 2016
  18. Frankfort MB's

    Frankfort MB's Well-Known Member

    What's up with the no filter issue??? Ive ran mine like that for about 150 miles no issues. I just haven't rejetted it yet (which I need to do)
    A quick 1-2 mile ride will not hurt it (unless your in a rocky dusty area)

    I was just saying to use it as test to see if he was running rich. Quick easy test.
    WINDY CITY BOB likes this.
  19. Frankfort MB's

    Frankfort MB's Well-Known Member

    Besides, a cylinder isn't that expensive or hard to replace if something did go wrong (Which shouldn't happen)