Hey all I have a 1994 tohatsu m90a 2 stoke 90hp motor that I installed on my fishing boat. Install went fine, motor was very clean and cared for. I had sat for about a year and a half prior to me putting it on my boat. Got everything hooked up. Fired up fine. Idles fine, no weird noise. Went to water test and it bogged down hard so I replaced plugs and I did a seafoam treatment of 1 can to 1 gallon of gas. Problem solved and it ran great for about 20 mins on a local pond. Took it yesterday to a larger lake to go fishing and it ran fine for the first run which was about 10 mins, 2nd run was fine then all of a sudden I got the bog down in power and felt like I lost a cylinder. I pulled the plugs to check and cyl 2 the spark plug gap had closed. No harsh noise or anything just a loss of power. I tried to scrape the carbon off it it was heavily covered. I opened it back up with a screw driver and it ran again for about a minute before it fouled out. I am planning on checking compression today and going to obtain a scope to see if there was any damage Inside the piston. IM wondering if the seafoam could have knocked carbon loose to shut the plug like that or am i in for a bigger problem. The plugs were swapped with ngk Br8hs-10, manual calls for b8hs-10, basically same plug minus the resistor in the one I put in. I can going to get the non resistor type plugs also. I didn’t have an extra on the boat to replace the shut one with. So I used the kicker motor to get back slowly. Thoughts?
