older Merc 200

[monte859]

I have a older 70's Merc 200 20hp with thunderbold ignition which starts reallly hard and will not idle untill warm. when idling after that the motor sounds like it sneezes which i believe is misfiring. I am unsure as to what to check any help would be appreciated. Thanks

 

[pondfisher]

Re: older Merc 200

Pull the plugs and look at them. If they are a light tan or lighter in color with little deposit you may be running too lean a mixture. The sneezing may be the motor not igniting the air/fuel mixture in the cylinder because insufficient fuel to get a burn. It's a place to start.

 

[monte859]

Re: older Merc 200

not sure as to where the adjustment would be on this carb only thing i can do is pull the carb and check the needle valve and float thanks for your reply the plugs are new.

 

[monte859]

Re: older Merc 200

ok took the carb apart again and the needle valve for the float appears to be sticking up in the housing it is not moving freely I am gonna try some carb cleaner in there to attempt and get to move smoother. I had the boat running today and I smoothed out the idle a bit but now when I when i pick the RPM's up the motor seems to bog out and blow a lot of blue smoke. I am thinking that one of the coil packs may be giving weak spark but am unsure of how to test this and what the proper amount of voltage is. I also pulled both plugs and the top cylinder is showing signs of ignition but the bottom plug seems to be wet and has no carbon on it. any suggestions???? oh yeah and I belive this motor is a 1974 or 75 judging by serial number also has trolling adjustment on the tiller handle but i use remote throttle controls and steering.

 

[monte859]

Re: older Merc 200

OK So I checked the compression on both cylinders and are both right at 124 and there is clean blue spark to both plugs. I Cleaned the card and got the needle valve to move freely. So I put it all back together and ran it on the muffs. Motors starts right up and idles and now will run at full throttle but still sounds like it misfires. I did notice that when I pumped the fuel bulb there was a fuel leaking from the underside of the carb would an air leak cause this? I ordered a gasket kit and a new needle valve hoping this fixes the issues any suggestions? I saw that Laddie seems to very knowledgable hoping he sees this!! thanks.