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

[KB_UK]

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.

 

[KB_UK]

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?

 

[crassius]

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?

 

[KB_UK]

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.

 

[crassius]

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

 

[KCvale]

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.

 

[FurryOnTheInside]

There's no gasket between the engine and the intake manifold. Could this be my problem?

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

 

[KB_UK]

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.

 

[butre]

your lack of an intake gasket is almost certainly the problem

 

[KB_UK]

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?