I know this is not your usual size motor you answer questions about but this has me stumped and hope you can help. On my little fishing boat with a 1976, 35hp Evenrude, when I try to crank it it barely will turn over acting like a dead or low battery. I charged the battery with the same result, then I put a new battery in with the same result. I pulled the plugs and tried cranking it that way and it spun over like nothing. i put one plug in and it would barely crank. with both plugs in it was the same deal. Also cranking without the plugs I got no liquid or anything blowing out so it wasn't trying to compress a liquid. I have one of those portable jumper batteries so I tried using it thinking that with it and the regular battery it would crank but it still would did not. Could you give me a direction of what else to look for?? Thank you, Frank
Start from the beginning.
How old is your battery? Have you had it load tested recently?
Check the cables for corrosion under the insulation if they are a few years old. Also, clean the oxidation from the ground contact points for the negative cable and starter.
10.5 volts is the maximum voltage drop you should see with the starter cranking an engine.
When the fields get hot on older starters, the insulation breaks down but not enough to stop completely. This is what is probably your problem. If it is an old one, it is time to get a new one.
The engine cranks better with the plugs wires off because they;re not using any voltage and not adding any additional resistance to the starting circuit.
Its always a guess from here, but I would say take your starter to be rebuit--it may only need new brushes. Or buy a new one. Do this only after making sure each and every connection and wire between battery and starter is tip top.
If after trying all of the above with no results, check your timing - if it's too far advanced for some reason, it will be hard to turn over with the plugs in regardless of how good your battery is.... on some older outboards, the timing can be thrown off when the prop hits a few things from time to time...