Help me get the YB 100 chookie going

Gidyup

Gday fellows,I have rescued a YB 100 from the scrap heap& am trying to get it running
I have spark ,fuel,& compression but she wont fire.
It doesn,t seem to be sucking through the carbie.
Can someone give me a rundown on how the induction system on these work .
Do they draw the fuel mix into the crank case & then into the cylinder?
Could it be crankshaft seals gone?
Do they have reed valves or what .
You probably Know by now ,I know stuff all about 2 strokes.
I just want to get it running for a chook chaser .

Thanks ,,Ray

Steve Searles · Posted: Tue Feb 16, 2010 7:20 am Post subject:

OK. That is a rotary valve carburated 100cc Yamaha. There is a rotary disc connected to the crank on this right side that has an opening in it. When the disc rotates it opens the intake "port" and will let the air/fuel mixture into the crankcase. (The disc sometimes can break but this is rare.) Then this mixture is sucked up thru the piston ports outside of the cylinder and dumped on top of the cylinder before it goes up and compresses the gases. Spark and then fire in the hole! Carb must be cleaned well with main and pilot jet clear, float working properly, etc. Choke is on top of the carb and the idle is a small rod on top of the carb as well that limits how far the slide goes down. That must be sliding properly as well. Exhaust must be free so a trick to get started is seeing if it will start without the exhaust hooked up. (Only run for a few minutes this way) Good luck, I have just resurected two all 100cc Yamahas. They were the two stroke king back in the late 60's and early 70's. PS: Have you had the carb off and gone thru in earnest???? What is that, a 1973 with that paint scheme???