Break In First time builder, engine won't idle, hard to start

Discussion in '2-Stroke Engines' started by KB_UK, Oct 11, 2016.

  1. KB_UK

    KB_UK Member

    Hey there. I just built a 66cc bike and I can't get it to run for more than a few seconds.

    I have spark. I have compression too, because its harder to pedal when I let go of the clutch. As it's a brand new engine I used a 5L petrol can to mix 4L of petrol with 250mL of Castrol 2-stroke oil, for 16:1 like it says in the manual.

    I pedal up to some speed, let go of the clutch, and it kicks in, but it doesn't idle. I can give it some gas and it'll rev up a bit, but over time it becomes less effective. I'd say it runs for about 30 seconds, and the power gradually drops off. In the end I have to pedal it to keep the engine turning over, even if I give it full throttle.

    The behaviour is the same no matter if I start with the choke or not. It's all standard parts as come with the kit on ebay. Normal NT carb, I haven't messed with the idle screw or anything yet. There's no obvious rookie mistakes like an upside down carb.

    One thing I'll say I noticed is that the throttle cable seemed very very slack when I installed it. I had to unscrew the barrel adjuster very far to take it up. I watched the carb needle go up and down when I did that, so it looked right, but I'm not sure.

    I'm sure there's something I've done wrong, maybe the carb, I don't know. I thought it was best to ask the wise elders before I start tinkering, in case I make it worse.

  2. KB_UK

    KB_UK Member

    UPDATE: just double checked the carb needle and throttle cable, they're installed properly. Behaviour is worse, engine can now at no point power the bike. As soon as I stop pedalling, Puff! stop. As soon as I pull the clutch lever, it dies.

    Choke doesn't change anything. Neither does trying to rev it, or messing with the idle screw. The engine actually needs me to pedal just to keep turning over, but you can hear it firing!

    There's also black oil dripping out the exhaust pipe. Normal?

    EDIT: I just took a close look at the engine. There's no gasket between the engine and the intake manifold. Could this be my problem?
    Last edited: Oct 11, 2016
  3. crassius

    crassius Well-Known Member

    sounds like it may be way too rich - check by dropping needle all the way down to see if it changes

    was fuel can shaken well before pouring into tank?

    any sign of oil residue around head gasket area?

    if plug cap is plastic, does it grip solidly to plug?
  4. KB_UK

    KB_UK Member

    Thanks for the advice. When you say drop the needle down, do you mean adjust the throttle cable/idle screw to lower the needle's normal position, or do you mean to move the clip on the needle?

    Gave the fuel a good long strong shake in a 5L plastic can before filling the bike.

    No residue around the head gasket. Dry as a bone.

    Plug cap seems to grip the spark plug okay (I've never owned anything with an engine before so have no frame of reference) . I can feel it click on and off when I push and pull it. I've tested for spark by taking the plug out, resting it on top of the cylinder head bolts, and then wheeling the bike. I got good blueish white sparks, and even the odd flame from fumes coming out of the plug hole!

    The spark plug itself feels wet to the touch and is very shiny.
  5. crassius

    crassius Well-Known Member

    yes, dropping needle means putting clip at highest position to let the needle sit lower in the jet
  6. KCvale

    KCvale Motorized Bicycle Vendor

    First of all is your carb level, a picture of your setup would really help.
    Since it has been flooding you need to blow out any raw fuel sitting in the crankcase.
    With the plug out and clutch released, pedals up and down the street to blow all the crap out of the plug hole.
    It's easy, no compression ;-}

    I'd put the clip on the second notch down.
  7. FurryOnTheInside

    FurryOnTheInside Well-Known Member

    It can't be helping. I would definitely fix that, then do the other things mentioned above.
  8. KB_UK

    KB_UK Member

    Carb looks level to me. I'll try take a photo soon but it's dark right now.

    I'll go unflood it and try leaning it out like you said. I get the sinking feeling I'm going to end up having to look in the float bowl, because on all the "how to" videos the clip is the same position on their needle as is is on mine.

    Limited to trying it out after dark because I live next to a police station, and I'm sure they'd have something to say about it.
  9. butre

    butre Well-Known Member

    your lack of an intake gasket is almost certainly the problem
  10. KB_UK

    KB_UK Member

    Just pulled the spark plug and pedalled around like you said. I'm not sure how I'm supposed to know when to stop? I don't want to seize it.

    No start with the clip moved. Might still be flooded. Have no earthly idea how to tell.

    Where can I get a gasket from that doesn't involve waiting for a month for an ebay delivery from china?
  11. FurryOnTheInside

    FurryOnTheInside Well-Known Member

    Not an expert here but just so you can have a quick reply. I read that you keep doing it til the fuel&oil stops coming out. It won't seize, afaik.

    No point in even trying to adjust the carburetion until the intake leak is fixed. Probably safer that it doesn't start.

    Fiber gasket material can be bought as a sheet from any auto repair shop. Just cut out the shape of the intake manifold surface using a craft knife. The stock one is so cr@p you can't do worse. :)

    Check for leaks elsewhere on the intake by spraying starting fluid on the outside of it, after/if you have the engine running.
  12. KB_UK

    KB_UK Member

    I'm having a brain moment - me pedalling up and down the street to unflood it won't be doing any good if I've still got the carb attached, will it...
  13. FurryOnTheInside

    FurryOnTheInside Well-Known Member

    Good point. Petcock needs to be closed.
  14. KB_UK

    KB_UK Member

    Too knackered now, will have a go in the alley in the morning.
  15. FurryOnTheInside

    FurryOnTheInside Well-Known Member

    I'm glad I'm not your neighbour LOL. :p
  16. KB_UK

    KB_UK Member

    Late night experimentation... checked fuel was off off, took spark plug out, and pedalled all the way to the supermarket and back. Hard work. Still no idea if it's flooded. I feel like taking the engine out and just tipping the bugger over and seeing if anything pours out the intake.

    upon return, fitted the spark plug and noticed the wire felt very loose no matter what. Tried putting the wire on the plug while it's not fitted to the engine... the only thing holding it on is the rubber around the bottom. As I feared, no spark now.

    I'm amazed. Just unplugging/plugging the spark plug wire a few times has actually worn that out? Can I sleeve it with tinfoil or is this going to be expensive?

    No idea where to get gasket materials from other than the internet. Halfords doesn't stock any, and if the exhaust gasket is anything to go by, the material I need is 4mm thick or so which doesn't seem to exist on ebay anyway. Surely these gaskets are actually just generic? It's a pipe with a bolt on each side, I bet if I knew what to search for I'd find one in 30 seconds. Putting in "80cc intake manifold gasket" or the like gets me Chinese sellers.

    But what bugs me is that when turning the engine over, the throttle does change the tone of the engine. Which makes me think there's no significant leak from the lack of intake gasket. Or maybe that doesn't matter. It's 4am and after trying to get this thing to work, I know less about 2-strokes than before I built it.
    Last edited: Oct 12, 2016
  17. FurryOnTheInside

    FurryOnTheInside Well-Known Member

    I think you have both gaskets on the exhaust side.. if that's even possible. The 4mm comment made me think that.

    No one's saying that you don't have multiple/compound malfunctions. The carbs don't come adjusted properly, but to adjust it you must have a sealed intake first.

    Im sure you have unflooded (or whatever the word is) it enough by now. :)

    Is there a local independent moped & motorscooter shop or a lawnmower and garden tools hire shop that might have fibre gasket making sheets and a plug wire?
  18. crassius

    crassius Well-Known Member

    if you have a tube of non-hardening permatex form-a-gasket - that will work to seal the intake

    if your plug cap is plastic, then you've probably lost the inner brass piece - It unscrews from the wire and can be replaced by a good NGK cap (I prefer a zero-resistance cap like the LZFH) - in a pinch, one can strip back the end of the wire a bit and wrap it around plug and hold it with a nut
  19. KB_UK

    KB_UK Member

    Since its what passes for daytime I've took some pictures.

    Blurry but the best I can do. Exhaust gasket looks very thick but I am sure it's only one. air filter is off because the choke was too loose and kept falling to the on position.

    Brass part of spark plug socket thingie is still there. I removed the little rubber skirt thing that's supposed to keep water out so that I can check see how much grip it's providing. The answer is none. None at all. No wonder it's not sparking now.

    EDIT: yep, both gaskets were on the exhaust. The intake was already fitted to the engine when I took it out of the box. Obviously that Chinese sense of attention to detail at the factory.
  20. FurryOnTheInside

    FurryOnTheInside Well-Known Member

    Lose the front mudguard, like right now.
    It's the worst kind (the wire support at the back, deadly), I would not trust it even with all the loctite in the world on the main (top) bolt.