I think the amount of current required on the solenoid is vastly in appreciated on many small motors. We think it’s only a solenoid so a few amps at most. The report sheet on my Bosch starter for the M25 reported that it took 31amps to push the bending into place and 10 amps to hold it there. That a lot of current if even for a short duration. Upping the wire gauge will help, but the switches are typically rated at 7 amps with the better ones at 20 Amps. The response from the starter was 100% better after installing a simple 60/40 relay. Plus I’m not sending all that current down and back 30’.
Les
I see an average of between 8A and 18A on most starter solenoids for sailboat AUX engines. We have a 1kW starter on the re-build bench right now that pulls 17.4A at 12.1V. Unlike the starter motor itself, the solenoid does not really have any
in-rush to speak of.
By the time you pass through 15' plus of small gauge wire, often 12GA to 16GA, a neutral safety switch, a starter-switch, fuses, terminations & the related corrosion, the voltage to the solenoid can be quite low and often not enough to do much.
The engine manufacturers often design for near "ideal" conditions but the marine environment is far from ideal.. Yanmar in-particular, has used various size wire for the starter solenoid, depending upon the vintage. I have seen as large as 10GA and as small as 14GA.
Something many are unaware of is that Yanmar also offered, on some engines, an
optional "starter relay". Some builders opted for the starter relay configuration. Island Packet is one of those builders who ordered Yanmar engines with the optional starter relay. These factory start relays are usually located right below the starter motor bolted to the engine block. You could pay Yanmar about $80.00 for one or grab one at any auto parts store for about $15.00 to as much as $34.00 for a premium Cole-Hersee.