My kid has 70cc bike that seem to run well until a couple days ago... now it will only idea while choked. If I try to ride it, it will "catch" very once in a while and begin to accelerate for a few feet, then lose power. It will not run un-choked at all.

I can also lift the rear end and it seems to run fine while accelerating and I can even un-choke it while WOT. But as soon as it returns close to idle it dies.

DOES this sound like a compression issue? I was thinking carb, but the inline filter is clear and the most noticeable issue is only under load.

edit: Let me add that I did a compression test, but the results were so off that they lead me to believe the gauge may be faulty since the bike will run at all...

 

Ya gotta clean the carb first. Dirt can come from vent lines too.

 

Carb cleaned and no spark arrestor... At least it idles now I choked and will move with my 4 year older in it... It still loses all power under any moderate load.

Compression shows 30 psi max... Would it even run on that little compression?

 

I'd think no.

 

I had a Honda 70, two wheeler in to "fix for Christmas" a couple of years back. Did run but no guts at all, and quite bad to start, checked compression, less than 20psi. When I took the cylinder off, the rings were so worn they fell through the cylinder when I put them in to check ring gaps. Fitted a Chinese cheapo cylinder kit, ran fine after that. However a sudden drop in compression indicates either valve problems or a piston seizure. Try adjusting valve clearances first.

 

It's a 2 stroke, so no valves. I used my buddies gauges and my gauge is, in fact, faulty. 110psi and 15% leakage on leakdown.

Took carb off again and played around with it. I found that if I put my fingers over the 2 small holes where the air box connects to the carb, it runs perfect.

Where should I start with the air screw to adjust it?