New engine gets put-put, only sometimes :/

hey gang, I'm sure this ground has been covered a few times but I'm hoping to get some direction.

I finally got my kit together and now I'm tackling the engine actually running.

The problem is that at best I've gotten the bike to start maybe 5 times, after getting it up to a speed, 10-12 MPH and then pedaling hard and it will sputter on and run for maybe half a block or about a minute at a low speed then it starts to sputter out.

All the other-hundred times I'm just exhausting myself pedaling with this engine making a "waahhhhhhrrrrr" sound and doesn't kick over.

It never continues to run with the clutch disengaged either.

What I've tried so far:

*The pin in the carb slide, I started at the top and moved it down one by one to the last setting, no real change.

*I tightened the spark plug in, funny it may have actually started better when the spark plug was a little loose but not too loose.

*I played with the idle screw on the side of the carb, similarly, no effect.

*Not sure if the choke should be up/closed/on or if it should be down/open/off or but I've tried both and it didn't seem to matter.

*I've bypassed the kill switch and tried switching the wires, in fact it only starts when black is wired to blue and blue is wired to black (wtf??)

My engine is a standard china girl as you guys call them. The break in fuel is mixed at 16:1 because that's what the chinese instructions say to do.

Cold and wet for the last two days when I've been trying to start it, but it's CA so, mid 40s.

I really hope I can get some guidance on this, I am so close and when it DOES work it feels like magic!

Thanks for the replies,

so to clarify, I did get the NGK plug and new sparkplug wire (resistance wire but lots of people on the forums have said that's OK) and I also added a little fuel filter, 2 bucks from spooky tooth also I cut all new gaskets from paper at the auto store. This was all during the build phase.

I realize people have lots of opinons on breaking ratios but I know a guy and he ran his motor at 16:1 to break in and that's what the Chinese instructions recommend.

Now, about "going over everything...and suchlike" haha I'm a noob but I've learned a lot on this forum. I've checked all the things I said in my post and I've made sure it's all tight.

The engine starts if you pedal hard, but it after it gets a little warmed up it starts crapping out.

Thanks guys, these are some interesting ideas. I will post an update when I can spend some time playing with it.

UPDATE: sorry it took so long but when I get home from work it's dark and has been raining, so I only have the weekends to work on this.

I'm about ready to put this thing in the box "return to sender"!

I loosened the cap and tried to get it to start, today it's being a bigger ***** than it was the other day!

I'm out of breath from the process (not that I'm in peak physical condition anyway).

The only way it ever started was getting up to over 10MPH and letting in the clutch, peddling HARD with WOT until it puttered.

THIS time, I got maybe one or two puts out of the thing the rest of the time I'm just pushing hard and it's not going.

I don't know if anyone can help me at this point. I don't mind learning as I go but with this blasted thing I never GO!

UPDATE as of TODAY (10 minutes ago in fact)

I got the little girl running!

Here are the adjustments I made:

moved the pin back to the second detent from the last one, so I don't flood the engine when it doesn't start the first couple times.

I didn't see gas flowing into the fule line so I cut a bunch of slack off of it so is wasn't so "S" curved and I took out the filter that was screwed to the fule valve inside the tank.

When I unscrewed it a bunch of little black "dirt" or "pebbles" came out mixed in the gas.

Now it starts up every time!

Woot!

Time to break this sucker in!