I have a 1978 Mercury 800 that we took out for the first time in years. It starts pretty easy and idles Ok, not perfect but it does it. But it won't put a 15' Siverline tri-hull with 2 people up on a plane. The controls definitely open the throttles all the way. Water spits out pee hole pretty good with rpm but not at idle. I started pulling plug wires one by one when idling and get no change on the top. Back home I pulled the plug and checked for spark, it has great spark on #1. The plug was clean and dry as new even after running. I don't think that cylinder is getting fuel. #2 looks like a working plug, a little wet, some browning after running, and if you pull #2 wire at idle (or anything besides the top) the motor dies. This motor only has 2 carbs so if #2 is working it is coming off the same carb as #1 so it's getting gas. With the plug out at idle putting my finger in the hole, there is a lot of air coming out each stroke but mysteriously if I seal the hole hard with my finger it kills the motor at idle. With the plug in it idles fine, with the plug out it idles fine, but if it's running with it out, plugging the plug hole kills the motor. Also there is some oil/gas in front of the carbs down in the bottom of the air intake pan like it might be spitting back out of a carb. I haven't done a compression test yet.
To me it seems that dry sparking cylinder isn't getting any fuel but seeing as how it shares a carb I don't think it's carb or fuel pump related. The only thing that would be different between 1 and 2 would be the reed valves. If it had a crankcase pressure problem wouldn't it affect all the cylinders? This motor as far as I can tell has the reed valves buried inside. Does it need to have everything pulled apart to even look at them, as in powerhead pulled, case split open? I will do a compression test to see if they all are even, but if I have to open it all up what else should I go ahead and replace? Is it even worth it? This was my dad's boat and he recently passed away I was just trying to sell it for my stepmom but figured the motor was the most valuable part. I thought it was running good but figured I better take it out and I'm glad I did, I hate selling somebody a big problem. I'm pretty mechanical and have rebuilt all kinds of engines and transmissions but never a 2 stroke outboard or any outboard or any 2 stroke for that matter. What would I be looking at total for parts if I did decide to tackle this?
Thanks for the help on a project I really don't need right now LOL!
Bryan
To me it seems that dry sparking cylinder isn't getting any fuel but seeing as how it shares a carb I don't think it's carb or fuel pump related. The only thing that would be different between 1 and 2 would be the reed valves. If it had a crankcase pressure problem wouldn't it affect all the cylinders? This motor as far as I can tell has the reed valves buried inside. Does it need to have everything pulled apart to even look at them, as in powerhead pulled, case split open? I will do a compression test to see if they all are even, but if I have to open it all up what else should I go ahead and replace? Is it even worth it? This was my dad's boat and he recently passed away I was just trying to sell it for my stepmom but figured the motor was the most valuable part. I thought it was running good but figured I better take it out and I'm glad I did, I hate selling somebody a big problem. I'm pretty mechanical and have rebuilt all kinds of engines and transmissions but never a 2 stroke outboard or any outboard or any 2 stroke for that matter. What would I be looking at total for parts if I did decide to tackle this?
Thanks for the help on a project I really don't need right now LOL!
Bryan
