I have a '96 48 HP Johnson. Replaced impeller and thermostat last weekend and took her out this morning for a lake run. Was a little on the cool side this morning (53*) and engine was a little hard to start (always started quick before). Once started it did not want to idle without the fast idle lever all the way up. Ordinarily with fast idle all the way up it revs +2000 rpm. Today with it up barely kept it at 1000. I let it run this way for at least 5 minutes. When I hit the primer switch it would kick up the rpm's for a moment then fall back down. I was finally able to back it off the trailer and after a couple of tries was able to kick into gear and head out. I gave it full throttle and it ran fine to my fishing hole and as I backed it off to idle in she shut down. Ok, fine, I dropped the trolling motor and went to work. Nothing happening here so decided to move to another spot. Cranked her up and same thing. Didn't want to idle, so I raised the fast idle lever and hit the primer switch. YIKES!!! It suddenly took off to 5000 rpm!! I turned off the key and pulled the kill switch but it ran on. I jumped to the back and disconnected the fuel line and prayed it would run out of gas before it threw shrapnel. It finally shut down so I took off the cowl for a look but saw nothing amiss. Ok, fishing is over for today so lets get back to the dock. I cranked it up once more, slammed it into gear and gave it full throttle. Took a couple of tries but finally got it to go and made it back to the nowake zone. With my hand on the key I put it in neutral and as soon as it hit neutral it started to take off again. I quickly turned off the key before it was able to get over 2500 rpm and she shut down. I used the trolling motor to get her loaded and took her home. I pulled both spark plugs and they were both a nice brown with a little gas/oil residue. I inspected the pistons and the top one was quite clean with just a little peppering of carbon. The bottom had a light coat of carbon over the whole surface. I have run seafoam on my last three tanks of gas (6 gallon tank). All hoses and wires look good. The only thing I removed when I did the impeller was the starter. Any ideas would be most appreciated. Thanks in advance.
