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1983 Merc 90HP inline 6cyl

1

1ton

Contributing Member
I have the above engine and would like to know how to test compression on #6 cylinder. Tight in the lower pan my compression hose wont go on. Is there a swivel or 90 degree adapter that can be purchased or has anyone made one?

Complaint:2000 RPM max @ WTO

Several control box wires and stator has been changed. Spark jumped 3/8 gap on all cylinders. 16psi difference between cyl 1 and cyl 2, 1 being the lowest. Triple checked #1 and cant get on #6.

Any ideas? Thanks
 
Merc dealers had a special adapter to get in there.-------Or you can remove intake bypass covers to look at piston / rings.----Also will let you ook for missing bleed restrictors.----Is this motor " new to you " ??-----Did this issue show up suddenly ?----Do not run it any more untill you determine the cause.------A blocked carburetor jet can lead to major engine damage.-----What compression do you read on the 5 cylinders ?---Are all the wires from powerpacks going to the correct coils ?------Could be a reed valve issue.----Could be a ruptured diaphragm in the fuel pump too.----Could be an issue with bottom crankshaft seal.------Blocked exhaust housing ?
 
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Yes new to me. Service manual on the way. Guy bought the boat took it to the lake would not get up on plane or go above 2000rpm. Also stated amp gauge jumped. Local marina had recently performed a "tune up". On a Winner bass boat. Compression: 1-5 136,146.5,149,148,144. #6? Was moving to the fuel pump next. Thought of the blocked exhaust
 
No telling what a previous owner may have messed with.--------Follow your manual when it comes in.-----My guess is that # 6 will have good compression too.----It is usually # 1 or # 3 that have issues with compression.
 
Previous owner always went to a local dealer repair shop. I'm going to run some more basic checks before the manual gets here. Firing order off or fuel restriction or........ Clogged exhaust would be a big job. Thanks for the help.

Get stuck later on or find the problem will reply
 
I am there to do any inspection.-----I do not know where the motor was.----Drop the lower unit and shine a flashlight up the exhaust.------Simple if critters built a nest in there.
 
I have a 2003 mercury 25hp four stroke...it will start sometimes and run fine and then die out of nowhere...other times it will start run for 1-2 seconds and not and not do anything even after 50 pulls any ideas?
 
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