I bought a Moto 4 last year and seem to be having problems with it. When I first got it I could get it to crank and run for about ten minutes then it would stop running. After checking the spark plug I saw that it was blackened. I figured the problem was with the piston rings so I replaced those and I also put a new intake valve in. Every since then I have not been able to crank it. I have tried just about everything. When I put it back together I timed it correctly. The spark plug has a good spark. I took the air cleaner box off and when I cover the carb with my hand and I can feel it sucking as I turn the motor over. I have tried spraying some engine starter in it and it still will not do anything. It will not even fire once. Any idea on what it could be? Also there is a little lever beside the exhaust valve that says "ON" what does that do? Thanks

William

 

I wanted to add that I have noticed that two turns of the crankshaft turns the cam gear once. Could I be off of timing by one turn of the crankshaft? Would that cause this problem? Could someone explain the compression stroke and why it would matter if you were off by one turn of the crankshaft since at both points it would be TDC?

 

You are fine with the crankshaft as long as the " T " mark(TDC) is lined up with the mark or center of hole and the cam marks are lined. The piston will be up and both valves will be closed. This is the compression stroke. On the compression stroke the piston moves up while the valves are closed and compresses the fuel/air mixture.

 

Ok so then it is timed correctly. Any ideas on why it will not even fire once when I put engine starter in it?

 

did You adjust the valves? The lever You ask about is a compression release. It opens the exhaust valve to make rope starting easier.

 

How do I adjust the valves? I have not done that yet. Does the spark plug fire on every stroke of the piston?

 

Get the piston at TDC on compression stroke,valves closed. Remove the covers on the front and back of the head to get to the valves. I will find out the specs tomorrow and let You know. You measure the gap between the valve stem and the rocker arm. There will be an adjustment with a jam nut on it.

 

Could this cause it to not fire at all? Thanks for all the help.

 

yes

 

Any luck on finding the valve clearance?