Have a 1980 electric start 35 horse Johnson Seahorse that won't start. I had the battery in the basement all winter and it showed a full charge just before I went to the water. Ran good when I put it to bed last Oct. When I try to start it all I get is a half hearted attemt to roll over. Only once did I get a high rev going but then it went back to the slow crank. Any ideas?

Well I would check the battery for starters. Make sure its got a full charge and that there is plenty of fluid in it. Check the connections to the battery make sure they are good and clean, try to start your Motor again. Make sure if you have one that the lanyard kill switch is properly installed. After that I would start looking at the starter. Make sure all the connections are tight and clean. Next check the spark plugs for wear and clean em up or replace them. Finally make sure you have clean gas and pump the primer. By the sounds of it its an electrical problem, hope its an easy fix.

I would start with the battery. You said you kept it in the basement, but said nothing about keeping a maintainer on it or charging it once a month while you had it stored. You can't just stick a battery away for the winter and expect to have a good battery the next spring, ain't gonna happen.

Connect a voltmeter across the battery terminals and try to start the motor. If battery voltage is droping below 11 volts it's junk, actually if it's droping to 12 volts I wouldn't have it.

That motor has to spin at 250 rpm to make a good enough spark to fire the plugs. There is no way it's going to spin that fast on a bad battery, so you can spin it until the battery is totally run down and it will not fire.

Now, I'm still not going to say it will start, just saying it doesn't even have a chance to start if your not spinning it fast enough to make a good spark in the plugs. If you didn't properly winterize the motor, you could still have fuel and carburator problems but no need chasing that rabit until you get a battery that will spin it.

yes start with the battery. Have it checked. I have had batteries that said they where at full charge and they just would not take a charge. Infact had that this year. My TM batteries (3 of them about 4 years old)would not take any more charge the charger said they were full. well, first trip out and I was out of power in less than an hour. Got home plugged the charger in. Said it was charging. 10  minutes later said they where at full charge. Needless to say I just picked up 3 new batteries yesterday. Start there. Then look at the motor. Did you winterize it?

Took the battery down to the farm and home last night after work and had them put it on their charger for an hour. Took it home and hooked it back up to the motor. Bumped the starter and got rapid spin. I will have to wait until I get it to the water to try it as I don't have a set of earmufs, but it sure sounded different.

Ok, you've proved the starter works fine. Now I STRONGLY SUGGEST you buy a new battery. That battery can be the most expensive $50 you will ever try saving. I have very serious doubts about the condition of that battery and most likely your charging system is going to be going wide arss open all the time trying to keep it charged while in the boat. What can easily happen is it will burn out a $150 recitifier/regulator and possibly even a $280 stator and that does not include the $90 an hour a shop is going to charge to diagnose and repair it when it does quit. The first indication you will get, if it has a working tach, it will quit working. It's your motor and your money.

If it's a maintenance free, sealed battery, there is no real good test for it. Yea, you can take it to one of these places and they can put their little computer tester on it and say yea, it's good, show's 380 CCA but you look on the battery and it says it's a 550 CCA, daaa, where did the other half the battery go. Half the idiots that have those things don't know what it's really telling them. They throw their little 50 amp load tester on it for a few seconds and say's "holds a load". Put a 150 amp load tester on it and see how long it holds a load.

If it has caps you can take off, for less than $8 you can get a hydrometer with the float in it and check the specific gravity. Slow charge it with a small automatic charger until it cuts off, if will take enough charge to cut off, and then check each cell with a hydrometer. Should be at least 1.265 on all cells. Most likely yours will never make it half way up the white scale, much less to the green.

Sorry to sound so blount, but I hate seeing people spend bunches of hard earned money trying so save a buck.

Some good advice from Way2slow.  Could save you some serious headaches, and cash, in the long run.