Not positive it's 70cc

Discussion in '2-Stroke Engines' started by Blue Max, Dec 27, 2007.

Tags: Add Tags
  1. Blue Max

    Blue Max Guest

    Hey guys. I just fired my chinese 70cc up tonight. I'm really happy with how it went together and everything was ready to go out of the box, like the carb and throttle assembly. Though I didn't file the drive sprocket through lack of a decent file and desire to take it out to get at it properly. It's dark and wet out so I didn't do anything rash. Was pleased how it started, but it did bog down considerably. I'm about 260 pounds so it has a load to push. How can I postively ID the engine as a 70cc?:???: Z-Box Engines here in Australia does give bore and stroke details for both sizes. The 70cc bore is 47mm and the 48 is 40mm. Stroke is the same. But I doubt I'll be taking the head off to check. lol First one I've ever ridden so I can't compare to a 48cc.
    Last edited by a moderator: Dec 27, 2007

  2. Bean Oil

    Bean Oil Guest

    CoRngratulations, sir! :D

    These engines take a few miles to break in... like at least 100. Also, what 2-stroke oil are you using but more importantly, what mix ratio? Bikers here have quoted mixes of 20:1 to 25:1 for the engine's intial use. Though I'm a fan of castor oil use in 2-cycle engines, I am also impressed by the newest generation of full synthetic oils... I'm using pre-mix-only Motul 800. For my first gallon I mixed at 25:1 and from then on 32:1. I'm halfway through my fourth gallon of California (10% ethanol) 87 octane.

    The engine will become a little stronger over the first five rides of at least 10 miles each, and the engine needs to be in the upper-middle of a comfortable rev band to output anything considered remotely exciting. When you get a chance, toss that Chinese spark plug and get hold of an NGK B8HS (colder) or a B6HS (hotter) spark plug.

    Also, these engines have a fairly low static compression ratio: somewhere around 7:1 which is not going to win any races... As for it's actual displacement, it is more than likely 67.3cc. The only way to know for sure, obviously, is to physically measure the bore and stroke.

  3. Blue Max

    Blue Max Guest

    Thanks Bean Oil. Your question about the oil ratio did get me thinking. I'm going to remix some fresh 95 octane in the morning (a few hours heh). I'm a little vague on the fuel I had, but I guessed it was 20:1. I adjusted it accordingly to 16:1 or so I thought. I used Valvoline 2 stroke oil, which seems suitable for the application. I'm thinking it may have been a much higher ratio fuel :-/..oh well no matter. Just hope everything is bedding in nicely. Otherwise I guess I'll be seeing the bore and stroke sooner than I'd hoped..hah :eek:

    Thanks for the tips and I'll let you know how things pan out tomorrow.:cool:
    Last edited by a moderator: Dec 27, 2007
  4. Bean Oil

    Bean Oil Guest


    Believe it or not, using too-high an octane can actually reduce power output... unless the ign timing as noticeably advanced, that is.

    A high-octane gasoline is slower-burning and since our engines have such low compression, I'd use the lowest commonly-available major name-brand gasoline available. Over here where I live, that's 87 octane... dunno how Aus rates 'em, but if you have an 89 I'd start there first.

    Good luck, and pls keep us posted on the break-in and the performance.

  5. Blue Max

    Blue Max Guest

    Thanks for the heads up. I'll have to get some more fuel and start again.:lol:
    I was using some fuel I have at home here. 91 is our regular unleaded octane level. Although our 10% Ethanol Blend is sold here as 91, it is actually more like 95 upward, so I guess that is not a good idea.

    I did a street run early this morning with some 16:1 with the ethanol blend (the 95:oops:) and it seemed alot happier. As was I. :grin: I do have some hills around and was impressed it made it up an incline near my house, albiet with a little peddle assistance.

    Cheers for now.

  6. Scottm

    Scottm Guest

    I read it somewhere besides the papers that came with my motors, don't use synthetic until it's broke in. Like Bean said, just take it easy for the first 100+ miles, each time you ride you will find a little more power.
    Have fun
    There's plenty of arguments in other threads about the actual bore size. I'll let you do the research. I think the biggest issue was a seller claiming 80cc when it was actually 68.
  7. Skyliner70cc

    Skyliner70cc Active Member

    For a 260 lb rider, I'd ditch the 44 tooth and put on a 48 or 50 tooth sprocket.
  8. iron_monkey

    iron_monkey Guest

    I dont really notice any significant increase in power since day one. I have one of the cheaper Z Box sold "Skystar" engines that are inferior to the regular Z box range.

    Then again Im only 62 kg so it really didnt matter and if there was more power it wouldnt be noticeable. Theres so much more torque than needed with the 44 tooth that I guess even a 30 tooth sprocket would do for me.
    Last edited by a moderator: Dec 29, 2007
  9. why not use synthetic? Isnt it far more superior than any mineral product out there? I use only Royal Purple in my truck and it seems to work better than any other i have used, so shoulntt it apply to all lubrication?