Re: Motor sputters after about 30 minutes of running
Welcome to Iboats, Doug. I've got the Johnson version of that engine, and have been messing around with it for years. <br /><br />If the RPMs are picking up and you're not going any faster, the most likely reason for this would be a spun propeller hub letting go. There's a rubber insert between the hub (pin driven part) and the outer part of the propeller. The simple way to check this is to remove the prop cone, and put a mark from the hub to the outer casing of the prop. Then put the cone back on and run the engine until it slips again. Check your marks and see if they still line up. If they don't, the prop is spun. You can either get a new propeller, or a prop shop may be able to repair the old one for less money.<br /><br />As for the misfire - if you can get it to warm up and start misfiring, try disconnecting a plug and grounding it out. Then run the engine on the one cylinder. After that, compare it with running only on the other cylinder. That will isolate the problem to the ignition system. Another thing you should try is comparing the distance one spark will jump to the other.<br />Another thing to try would be attacking the ignition system up underneath the flywheel with a hair dryer, to try to cause the problem. If the problem does turn out to be ignition related, it's not bad. New ignition parts are cheap and available. In fact you can replace the whole thing for under $70.<br /><br />If the engine were overheating, you shouldn't be able to hold your hand on the top of the head for a couple seconds. I doubt this is your problem since the 28hps seem overcooled to me. They have no thermostat.<br />When was the last time the impeller was changed though?
