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Merc inline 6 w/ no power 1982 90 hp

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Yellowstreak

New member
new boater here with no outboard experience needs troubleshooting help. i have a 1982 Merc 90hp inline 6, 2 stroke "tower of no power". the motor was strored for 10 years. fuel was drained and motor was fogged. stayed indoors all but 2 years and was covered when outdoors. first outing, it made power and ran well. took it out again to get trim settings dialed in (power T&T pump needs rebuilt) and could not get full power. it starts and idles good, but cannot get above 1800-2200 rpm in gear without bogging down and shutting off. backing out of throttle slowly will allow motor to stay running but never reaching a planing speed. fuel tank, fuel lines, seperator are new, pump rebuilt. i run 100% gas with 2.5oz/gal 2 stroke oil. ran seafoam through for 2 hours while cruising to no avail. bulb seems about right while running and pumping it while advancing it doesn't do much. removed discharge hose at pump and squeezed bubble. getting about 2 oz per squeeze of clean gas. pulled bowl covers off 3 carbs. not a spec of contamination or varnish -looked brand new inside. floats and linkage look good too. only filter i find is the screen on the pump and the seperator i installed. where to now? thakns for any advice.
 
Re: Merc inline 6 w/ no power

Do a compression check on the cylinders after the engine has warmed up. You may have some stuck or worn rings since it sat so long.

Compression should be around 10% of each other. Bigger worries if you get 2 cylinders together with low compression. Could be the head gasket.

Could also be the stator (under the flywheel). Will need a multi-meter and a book with specs to test it and rest of electrical system.

Another issue may be overheating and your overheat sensor is not functioning. My old 1983 Erude 175 did the overheat thing and caused the engine to bog down and shutoff. Then after it cooled a few mins it started back up again.
 
Re: Merc inline 6 w/ no power

UPDATE: feel stupid that i was tracing what i thought were symptoms of a fuel problem. any decent mechanic knows the fuel or fire theory. after describing to a friend what the unburned oil looked like dripping from the prop exaust, (thick and grey)he suggested throwing an inductive timing light on each plug wire to check for fire to each cylinder. sure enough, #1,3,5 were not. how was i to know the motor wouldn't run rough as a jack hammer on half it's cylinders? seemed smooth to me. traced each dead plug back to each respective coil, and then back to one of the two switchboxes/power packs. manual says that a solid state device cannot be tested independantly w/ voltmeter. my two choices were test EVERYTHING in the innition system to rule all other possibilities ou,t or to switch the two powerpacks and see what happens. did so, and found that cylinders #3 & 5 ran but not #1. of course, now #2,4,6 were not hitting because they're on the bad power pack. so, coil #1 had s*** the bed too. put everything back like it was and ordered above parts and bulk plug wire from here. was pleasantly suprised that the MSRP on SELOC's online service manual/parts look-up were more than my actual cost. it afforded me more than 2nd day air freight. hope this info helps someone else. see ya on Keowee this sat.
 
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