Merc 402 won't rev

pocale

Cadet
Joined
May 15, 2011
Messages
7
Hi all,

My first post here :)

I bought an old boat with Mercury 40hp (402) blue band engine. The previous owner stored it outside for the winter (cold here).

Got it on water yesterday, after long time of cranking i got it running, but the problem is that the engine will not rev up good... it does not response to the throttle soon after off-idle... i tried running it full throttle for a while, and once a while occasionally the engine wakes up with good power for a few seconds, then come back to unresponsive mode. Carb/s need cleaning/rebuild??? choke stuck??? As mentioned, i am new to this engine, so tips/tricks and help are appreceated :)

btw, how the engine cover gets off? how can i identify the year of the engine?

thanks :)
 

pocale

Cadet
Joined
May 15, 2011
Messages
7
Re: Merc 402 won't rev



Did more troubleshooting today... engine running, the upper spark plug feels cold versus the other.. obviously running with only one cylinder now. no wonder it is a bit hard to start and lacks power.

As mentioned, sometimes, once a while the other cyl kicks in and engine revs up... but it lasts only a second or so.

no spark i guess... any ideas where to start fixing? thanks
 

aussieflash

Lieutenant Junior Grade
Joined
Feb 5, 2011
Messages
1,004
Re: Merc 402 won't rev

Find your serial number,then definitely get a manual.The 402 40 were around in the 70s.Try cleaning up all fuel related parts including tank, lines,carbs,pump,filters etc.
 

pocale

Cadet
Joined
May 15, 2011
Messages
7
Re: Merc 402 won't rev

thanks for reply.. i found the serial and this is year 78.

I think it is spark related problem, and as mentioned feels like running only on one cylinder. Any ideas?
How do i disassemble the top of the engine housing (where the pull-start is)?

?thanks
 
M

Maxz695

Guest
Re: Merc 402 won't rev

Check compression It,s indicating a bad switchbox 1 plug cold then firing. it will get worse and only 1 cylinder will fire period. Then time for a new switchbox. Happened to mel ast year. Try all the above mentioned first carb fuel pump plugs check all wires for fray and corrosion esspecially where the wires come out of the stator this is a propblem area on 402 and 40 HP. I have a 79 40 2 cyl 2 stroke. chang e the impellor and lower unit oil
 

pocale

Cadet
Joined
May 15, 2011
Messages
7
Re: Merc 402 won't rev

noticed the spark-wires are stiff as they were over 30years old :) and connectors corroded..
cleaned the spark-wire connectors and adjusted the spark-plug gap smaller and
now it works like a dream! have to replace the plugs and wires soon... hope she
stays good now and problem solved.

i replaced the gear oil already, impeller i have to replace someday.

I dont have much experience with boats, the steering wheel pulls to right, and if
i would let my hand off the wheel the boat would immediately turn right... is this because
of the engine/propeller torque? the boat has steel-cable steering,, i already checked the
cables, rollers and connectors are ok, should there be some friction component or counter-spring
to ease the steering?

thanks for help.
 

pocale

Cadet
Joined
May 15, 2011
Messages
7
Re: Merc 402 won't rev

Googled and found the trim-fin adjustment for the outboard.. now everything is fine :) happy boating to everyone and good fishing-luck :)
 
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