check for spark on all spark plugs. Had similar problem and found out 2 out of 4 sparkplugs werent firing. Put new power pack on and had all 4 sparking. Problem fixed. Could be carb problem too? Maybe fuel pump is weak or clogged?

 

my 90hp merc doin the exact same thing...im changin the plugs tmr and see if that fixes it

 

I will try and check the spark. I have read a bit about checking for spark and there seems to be a debate on how and what to look for. Any suggestions on methods for checking spark on a small outboard?

 

Changing the spark plugs is a common uneducated guess and marine plugs very rarely need changed unless fouled or have years of use on them!Checking the compression,ignition and gearcase are the three key things to check when trying to figure out what system has a problem!Most likely you have fuel or carb problems!When you changed the fuel did you drain the carbs and sample the fuel at the point were it feeds the carbs to make sure you have a good clean supply at the motor?Fuel fittings,primer bulbs and lines are common causes and even tank venting,when it boggs can you pump the bulb and it pick back up?Does the bulb stay firm while the engine is running?No more information than given,I would check the fuel at the bowls and clean the carbs!And from the sound of it check the oil in the lower unit!Hope this helps!

 

i have a johnson and it has a S.L.O.W. system that kicks in if the motor is getting hot. don't know nothing bout mercurys tho.

----If the engine overheats, the S.L.O.W. (Speed Limiting
Overheat Warning) protection system will immediately
limit the engine speed to 2000 RPM. If
the engine was running faster than 2000 RPM
when the S.L.O.W. system activated, it will shake
noticeably.

 

carb is dirty, bottom line, no questions asked, no exceptions ,period.

 

www.iboats.com has some good help