My Saito 150 has been sweet for 3 years. Today, it wouldn't start, or even fire. I changed the plug, set the valves a couple of times, check fuel flow, but got not even a pop. I'm confused, as I've had no trouble with any of my Saito that I couldn't correct with attention to valves or plugs. Any ideas? Could something have slipped inside?
You need three things to make an engine run: Air, fuel and fire. Four if you have a four stroke: Timing. All are easy to confirm.
Air: Is the carb open? Is the intake valve opening? Do you get a puff of air out the exhaust when you spin the engine over? Fuel: Is there fuel in the tank? Is the fuel line full of fuel? Is the needle valve open? Is fuel dripping out the carburetor after you prime the engine? Is the glow plug wet after several seconds of cranking? Fire: Does the glow plug glow with the glow ignitor attached? Have you tried a different plug anyway? (A plug that's worn out won't sustain combustion even with the glow ignitor attached; it needs the catalytic reaction of the platinum and the methanol.) Timing: Take out the glow plug and remove the valve covers. If you have a basic working knowledge of 4-cycle engines, you should be able to follow the combustion process and verify that the valves are opening and closing in the proper sequence. Piston at top dead center, both valves closed. Piston going down, both valves closed. Piston reaches bottom, exhaust valve opens. Piston goes back up, exhaust valve open. Piston reaches top, exhaust valve closes, intake valve opens. Piston goes down, intake valve open. Piston reaches bottom, intake valve closes. Piston goes back up, both valves closed.
I highly doubt anything "slipped." We're talking about solid steel gears here. Any "slippage" will result in a catastrophic engine failure.