Engine Trouble PLEASE help....AGAIN!! Engine stuttering

Discussion in '2-Stroke Engines' started by tbrookes2000, May 2, 2012.

  1. tbrookes2000

    tbrookes2000 New Member

    Hi All!
    Ok listen...I finally got my bike going good with the help of you all, and a new speed carb...but NOW...the engine (after about 200 miles) has started to "stutter"...[nahhhhnannnnnnaaanaaaannnnn...instead of Nnnnnnnnnnnn) it runs fine sometimes...then stutters...hits a bump.....stutters.......like it's not getting enough spark or the spark is intermittent. I have changed to a new CDI, new 8mm plug wire, and NGK and Autolite plug. But it STILL does it. I'm thinking it's the coil, or the magneto. I am ALSO thinking that a coil from a 65-66 Volkwagen might work. I'd liek to get a 12 volt magneto (I HAVE heard of them) to see if this would correct the problem. What do I do? I have gone to the lengths of even researching how to make a new higher powered CDI. ANY suggestions or pointed in the right directions would be MUCH appreciated! I have almost 350 miles on this bike (see pic) and I love riding it...Have about $450 invested so far (bike, kit, Accessories)) and willing to put more if it makes it better. HELP!

    Attached Files:

  2. darwin

    darwin Well-Known Member

    Usually a stutter is a fuel problem, sucking air, carb/float or fuel supply. Thats where I'd be looking. Generally an electric problem involves no spark or timing if keyway is sheared.
  3. motorpsycho

    motorpsycho Active Member

    are you sure it's not 4 stroking? your description sounds like 4 stroking to me...and since you added the new carb, it adds up.
    if it is 4 stroking, the air-fuel ratio is too rich.

    these engines don't have a coil....they have a cdi(which is different than a coil).
    the magneto is only about 6 volts, not sure how you'd get a 12 volt magneto to work.
    then with a 12 volt magneto, you'd need a compatable cdi (a v.w. coil will not work).
    I'm no expert on electronics or ignition systems, so please, someone correct me if i'm wrong.
  4. Skyliner70cc

    Skyliner70cc Active Member

    Did you clean out the new fuel tank before you ran your engine? Rust is common in a new tank and often clogs the carb. Did you remove the fuel filter that is built into the fuel valve and install a inline filter? I've have had similar engine issue with clogged filter in the valve filter and have gotten stranded.

    Good luck and please share what fixed your problem.
  5. tbrookes2000

    tbrookes2000 New Member

    PLEASE help....AGAIN!! reply

    Thanks for the info guys...with this info I'm going to get to work on it straight away...I'll let you know what worked. Thanks a bunch for the help!
  6. Al.Fisherman

    Al.Fisherman Active Member

    Also if not mentioned already, check your wires for GOOD connections, and don't use the frame as a ground. Also disconnect the kill switch, and see if it might be that.
  7. tbrookes2000

    tbrookes2000 New Member

    Again thanks :)

    Yeah...I cut the kill switch wires on the WAY to work on morning thinking that might be it. I have heard so many others say that these kill switches are junk so I thought no big loss...however...it did not good. So I'm working on the filter, leaning it, and checking for clogs as suggested. I will let all know how this comes out (fingers crossed)
  8. KCvale

    KCvale Motorized Bicycle Vendor

    What is your current gas type and oil mix?

    The thing is in my experience especially with non-customer repairs is it just don't matter.
    When a good motor starts running poorly the very first cheap and easy step I take is replace the fuel.
    Did you know gasoline has a half life of only 6 weeks or less?

    Drain all the current fuel from everything including carb and get yourself a clean fresh gallon of Premium Gas in a clean 1 gal gas can and add 4 oz of new 2-stroke synthetic oil to it (32:1) for your broke in motor is my advice to start with.

    Premium gas won't give you any more power, it is just a much cleaner fuel with less Ethanol junk which are additives that are not friendly to our bikes, and it has a bit longer shelf life.
    Heck, you could probably run these motors on diesel or kerosene in a pinch, but they would run like you describe so a very good place to start even if that isn't the main problem.

    If fresh fuel don't fix it, before you get to trying new ignition system parts what is the exact plug in it and how does it look?
    White, Tan, Gray, Black?
    You mentioned replacing the plug wire? What is that about?
    Better wiring is always better with these things, good for you ;-}

    When it comes to motors, after fuel it is all about spark as you know, but what makes that spark is no mystery, gap it right and you can get some kind of spark from most any plug, but even with great fuel a crappy plug or maybe just the wrong heat range number could cause a little loss of performance.

    Well now I have gone and and done it....
    The middle number in an NGK plug number is it's 'heat dissipating' ability.

    As for a good spark plug the NGK Iridium BPR7HIX - 5944 Stock Number. SBP has them.
    Note the 7, that is NGK's heat reference, that number can be anything from about 5 to 8.

    It works like this:

    Engine Speed and Load

    * If the engine is to be operated at high RPM, under a heavy load, or at high temperatures for long periods a colder heat range may be needed.
    * Conversely, if the engine is to be operated at low speeds or at low temperatures for long periods, a hotter heat range might be needed to prevent fouling.

    The higher that middle number is, the cooler you motor will run.


    If you live in Alaska go with the lowest number you can get.
    Live in the desert like me? Go high baby, I run the 7's here ;-}

    They are a tad bit longer than stock and add a bit more compression but I have heard some kits pistons hit it, Skyhawks don't so I don't know first hand but thought I better share that to.
    Last edited: May 3, 2012
  9. HeadSmess

    HeadSmess Well-Known Member

    ngk B (thread diameter) P(may hit piston) R(resistor) 5/6/7/8(heat range) H(threaded length) S(...who knows?)

    the B is important.

    the P may be important depending on piston height.

    the R may be important if you have a radio and may possibly prevent premature cdi failure

    the heat range, yes, is dependant on area and use. so a slow engine, cold engine, winter engine, uses a low plug, which gets hot. a fast engine, desert engine, uses a high number, a plug that stays cold....

    has no bearing on the temperature the engine then runs at. combustion temperature is unaffected.

    iridium is a few extra dollars for a plug that will last for roughly the life of five to ten engines....

    multi points are silly, and once again, extra dollars on uneccessary items
  10. tbrookes2000

    tbrookes2000 New Member

    Ok all. Heres the scoop.
    I have cleaned the tank, fuel line, carb, and gone to PREMIUM fuel instead of the regular unleaded. It DOES run MUCH better (although I havent changed to a hotter plug yet)...AND I have oiled the throttle cable.
    I rode it to work last Friday..it did it somewhat (the "odd running). I oiled the throttle cable before I left work..and I gota say....in 4 months of having this kit..I have never had such an enjoyable ride. SMOOTH, CONSISTANT running, steady "buzz" of the engine! I was able to actually watch the scenery, and what was on the road letting my mind wander instead of spending the whole trip LISTENING to the engine and going thru the "flow-chart" in my mind as to what might be causing this anomally. She DOES seem to run perfect in the afternoon when its hot (Im in Arizona), and still do it som in the morning...So I assume I might need a wee bit hotter plug.
    Thanks for ALL the help! Now that she runs like she's supposed to..I'll be going to work everyday and enjoying my rides more :))
  11. KCvale

    KCvale Motorized Bicycle Vendor

    Hi fellow Zonie ;-}
    I have been building and riding MB's here in Phoenix for close to 2 years now and the summer heat can be brutal on these 2-stroke air cooled motors and the rider as well you know ;-}

    1. Premium Fuel.
    Excellent choice, that's all I run, not because the higher octane helps, it is just typically cleaner fuel with less Ethanol, that **** is not friendly on our gas lines and does not burn near as well as gas without it.

    At 4 months you should be plenty broke in, mix 32:1 (1/2 cup quality synthetic 2-stroke oil to 1 gallon of gas).

    2. Oiled the throttle cable.
    Not a good choice, especially here in the desert.
    You don't fix a sluggish throttle by putting oil in the cable, Graphite maybe but never oil, it will soon be worse than it was and may cease to move at all over time.
    Too late now, the throttle cable is the one cable that has two ends so you can't pull the cable out that most likely wasn't the problem to begin with.

    Good 'throttle snap back' ranks right up their with dual brakes as a major safety thing. The LAST thing you want if you take a spill is the throttle sticking open.
    Just like no new build bike leaves my shop without front and rear brakes, they don't leave with a sticky throttle either. I know that sounds a little anal but I have a little higher set of standards for my builds than most.

    My solution is pretty simple.
    Never use the gas tank mount plates to hold your throttle cable, any cable for that matter, it pinches it causing friction in the cable.
    Then when I assemble the throttle I put a little dab of grease (not oil) between all the moving plastic parts that touch inside the throttle as well as a light smear on the handlebar the plastic throttle barrel rides on.

    3. Iridium Plug.
    I don't know about other motor brands but any Skyhawk motor will take an Iridium plug, I love the suckers, it's like a instant boost you can actually feel and I keep them in stock.
    With summer here in full force now an 8 is your best heat range bet for them.

    Being a fellow ZOnie check out my web site and sign up for the forum, the link is in my sig.

    Hope that helps ;-}
  12. tbrookes2000

    tbrookes2000 New Member

    Thanks KC! Yeh...registered...if you can PM me ..I have a question about the silver bike with the maxxis tires...BADASS! i wouldnt mind having one! Also if you could let me know what plug (Iridium) you would recommend for me to use in my bike. I ride from Maricopa to Chandler everyday and would like to get the most from my ride.
    Thanks! :)
  13. Lunardog

    Lunardog Member

    Sounds like a minor fuel/air mixture issue going on if it stutters a bit when cold and runs better when warmed up.
  14. KCvale

    KCvale Motorized Bicycle Vendor

    NGK BPR7HIX, maybe even an 8 for your long brutal ride.
    That full suspension Silver Shifter was actually mostly built by the customer.
    He got everything mounted but couldn't get it function mechanically so he brought it to me.

    66cc Skyhawk, high compression head, X-chamber, NuVinci hub with drum brake, completely upgraded electrical for everything but the Mag and kill button, etc.

    I don't know how much he had in it but it was at least $1200 in just parts.
  15. motorpsycho

    motorpsycho Active Member

    can you please elaborate on all of these?

    Premium fuel? Why do you think it's a good choice for these cheap 2 stroke engines?
    They are low compression and any high octane fuel that you put in them is just money going out the exhaust.
    High octane fuel is not required and is a waste of money. These engines run best on 87 octane.

    WHY is oiling the throttle cable not a good idea?
    I agree, you don't fix a sluggish throttle by oilin gthe cable...BUT, you DO maintain the throttle cable by oiling it.

    4 months to break an engine in?
    wow...that seems like an awefully long time. summer (in the midwest) will be over by then.
    Run 1 tank of fuel at 20:1, and then drop the mixture to 32:1 and you're good to go. (my opinion)

    Never use the gas tank mount plates to hold your throttle cable?
    if you do it right, and run the cable through the tank mounts so that it isn't bound up or smashed by the tank mount plates, it'll be perfectly fine.
    you have to make sure that the cable has freeplay and isn't bound up.
    I agree on the grease on the throttle assembly.
    on my bike for example, there is a gap between the gas tank studs and the gas tank mounting plates (with the tank tight against the top frame tube) I ran my throttle cable through that gap which allows the cable to move around. It's not bound up and is free to move.
    I guess in some cases, there will be someone who smashes their cable between the tank and the tank mounts which will bind it up.

    an irridium plug?
    I don't get that one. are there any proven results that it gives you a power boost?

    sure, irridium plugs will last a very long time, and will probably out last the engine. But really...just go with a standard ngk (b6hs or whichever works best for you).
    why waste the money on an irridium plug?
    do you really think that an engine runs hotter in the desert than it does in the midwest?
    think about it, an engine will get up to 250-300 degrees and ANY ouside air will cool it.
    if it's 100 degrees out or if it's 50 degrees out, the outside air temp will always bo cooler than the engine temp. Even if it gets really cold out, the engine will still build up heat in the 200-250 degree range.
    an air cooled engine will not run hotter because it's in a hotter climate.
    the only way an engine would run hotter than normal due to it's environment is if the outside air temp gets up above the operating temp of the engine i.e. 250 degrees plus.
    OR if the engine is running extremely lean.
    this is just my opinion, and my thoughts...I could be wrong.

    sorry but i don't want to come off, sounding like i'm knocking what you're saying. I just wanted to see why you specified these things, and to post up other options that work.
    Last edited: May 14, 2012
  16. Big Red

    Big Red Active Member


    1). Cheapest gas I can find. Stuffs too expensive as it is.
    2). I ALWAYS oil all of my cables at first install then every now and then as needed.
    3). I run perhaps 2 tanks for break in. Just want to make sure.
    4). I ALWAYS run the throttle cable through the tank mounts. It keeps them up out of the way and usually allows the cable to fall straight to the carb.
    5). B6HS... Thats all...
    Big Red.
  17. motorpsycho

    motorpsycho Active Member