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I get a reading of 3.9 to 4 volts measured at the starter solenoid when the starter is engaged. That seems a little low to me. I tested the voltage with the engine cold, about 55F, clutch engaged, with 20/50 oil in the crankcase. Age of the battery is unknown, but it look OK and is clean with clean connections and good cables. The charging system appears to work very well, with good regulation. Is 4 volts on the low side when cranking in mild weather?

What is the voltage across the actual battery terminals when cranking?

And more importantly what is the voltage at the coil terminal being fed from ign switch while cranking. 4 volts is low and the spark is usually very weak and often can't jump the plug gap when under compression if the voltage at the coil is much less than 5v.

Quote:

Yes, I would expect at least 4.2V.

I would check the voltage across the battery. Then I would check the voltage between the battery post and starter terminal (not the battery cable lug on the solenoid) when cranking. Should be very low, maybe 0.1V. An excess drop indicates either an undersize cable and/or a worn out starter solenoid.

Thanks. I did test at the battery side of the solenoid and got 3.9 to 4.0 on a Fluke digital meter. Didn't check the starter side, which I will do, and I haven't cleaned or tightened the ground cable to frame connection.

Are you using at least 0 AWG cables?