1981 mercury thonderbolt 40 hp

info404

Cadet
Joined
May 23, 2009
Messages
20
ok, so, for the last couple of trips, i had a problem starting my motor, i thought it was moisture getting into the engine from the drive to the lake. after about a 1/2 hour or so it would start and be fine all day. i really didn't worry about that. when i get home i always clean my plugs and fill with fresh gas, 50-1 ratio. the only thing i did different this time was add some marine stabil. it started fine on the water, but i had no power. it felt like it was running on one piston. i changed the plugs and again no power. when i throttled up it went fine then when i hit the throttle all the way it sort of lugged and felt like it was chokeing a bit, but kept running. i'm hopeing its a bad coil. i didn't check to see if it sparks yet and figured maybe one of you experts recognize the symptoms. i didn't have any problems with the carb. it just didn't power up to full power. any ideas?? thx to all takers in advance..04
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: 1981 mercury thonderbolt 40 hp

Compression test and new plugs.... See what that does..
 

info404

Cadet
Joined
May 23, 2009
Messages
20
Re: 1981 mercury thonderbolt 40 hp

achris, thx for the speedy answer. i checked the compresstion and its 120 on top and 120 on the bottom, with new plugs. could it be electrical? whats a good way to check for sparks without a guage, (crank in the dark?)
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,930
Re: 1981 mercury thonderbolt 40 hp

Download the CDI trobleshooting manual and test you ignition system...
 
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