Just thought I'd throw this out for general info... This year our 10 year old riding mower had trouble cranking. I of course blamed the battery, got a new one but didn't help. Was going to buy a starter (after checking all the connections) but a good friend suggested I "adjust the valves" ... Hmmm, that's something I never thought of. Change the oil, put gas in it,,, thats about it. So I adjusted the valves, (it's a 17.5 hp B&S) and yee haa !! It starts (cranks) like a new one !!
Only took about 10 minutes,,, very easy. Reason is when the valves get loose,, and they will over time, it raises the compression, making it hard to turn over.
So with that I got to thinking I've had the exact same problem with the 95 Onan 4K genny in the mh. Starts and runs ok, but it has had trouble cranking sometimes every since we've had it. I of course have blamed electrical connections, but I've cleaned every one I can find. So,,,, since I don't know when Or If it has ever had the valves adjusted, with 1800 hrs on it,,, I'll be doing that this week. Hopefully it's as easy as the mower was... Have a great day !