My neighbor gave me a 150. Battery shot. Put a new battery in, cranks good. Wouldn't start. Pulled plug and grounded it against frame while cranking. Nevery saw any spark or sign of fire. I thought I had an electrical problem. Put plug back in and took off gas tank.....etc to get to carb. A little gas in the intake and she fired proving plug was firing. The rubber elbow between intake and carb was cracked. I repaired it with so high heat silicone for the time being. Put it back on. Float seems to be working, carb seems clean. The shut off? solenoid on the carb doesn't move when you power it. With it removed I held my thumb over the hole it goes in and the engine tried to run. With it in place I could squirt some gas in the back of the carb and the engine would run in spirts. No I can't get it to fire no matter what. I'm really confused. Tried a new plug thinking that one had a intermittent short. Where does the exciter signal come from that feeds the coil? The coil shows almost a dead short, 1 ohm reading, when testing incoming wire to the ground. >>>>>>>>>>>>>Help.

 

The solenoid on the carburetor is a bystarter valve. It is an automatic choke of sorts, only instead of starving (choking) the intake from getting enough air (raising the fuel air ratio) it instead opens up another fuel pathway adding more fuel to the fuel air mix when the engine is cold. It is powered by 12 volts, or 12 volts AC equivalent when the engine is *running* (as compared to when the engine is stopped but the ignition is on). This 12 volts (or equivalent) heats up that thing you call a solenoid over a few minutes. This heat expands a wax pellet which pushes a rod that slowly over several minutes closes off that extra fuel passage.

For a procedure on testing the bystarter valve go to:

Troubleshooting

Then chose the "electric choke" link.

When you say: Where does the exciter signal come from that feeds the coil? What coil? Are we still talking about the bystarter valve, or are we talking about the ignition coil? The ignition coil resistance is typically less than an ohm (but not zero ohms). It is driven by the output of the CDI (and acronym for "[C]apacitive [D]ischarge [i]gnition).