40hp 4cyl wont rev above 3000rpm

M

mgjtkt

Seaman
Joined
Apr 19, 2010
Messages
62
40hp 4 cylinder OGO36267 1993--
Have checked compression,98psi
new plugs,
spark 7/16"
dva voltage to coils ok
stator & trigger OK per book
removed yel & blk kill wires
unhooked yellow wires from stator
put clear gas line on to carb, bulb is firm.
Butterflys are opening all the way and plugs all look the same (wet) after cutting it off from wide open
Motor starts and idles OK but when you throttle up it goes to approx. 2500-3000 then just bogs. Problem started while running about 5000 rpm and boat slowed and has been that way since.What should I try next?
 
Barnacle_Bill

Barnacle_Bill

Admiral
Joined
Feb 8, 2004
Messages
6,469
Re: 40hp 4cyl wont rev above 3000rpm

You may have some trash in the carbs or you may have a fuel pump problem. I would rebuild the fuel pump using a kit from Mercury. They contain new style check valves and instructions on how to install them. The old style have rubber around the outer edges and ethanol (according to Mercury) causes them to curl up and not seal properly. This causes high RPM problems.
 
L

ledzeppelin135

Petty Officer 2nd Class
Joined
Jul 27, 2011
Messages
129
Re: 40hp 4cyl wont rev above 3000rpm

I have had the same problem, and no solution. It is a 1983 50hp merc 4 cyl.
 
M

mgjtkt

Seaman
Joined
Apr 19, 2010
Messages
62
Re: 40hp 4cyl wont rev above 3000rpm

Finally! Cleaned carbs AGAIN and found a small piece of trash in the main jet for the lower carb. I used a piece of stranded copper wire to use as a brush for the jet.
 
C

crazyhunter

Petty Officer 2nd Class
Joined
Jan 25, 2012
Messages
128
Re: 40hp 4cyl wont rev above 3000rpm

i have a 1990 40hp 4cyl and i am having the same problem how hard are the carborators to get off?
 
M

mgjtkt

Seaman
Joined
Apr 19, 2010
Messages
62
Re: 40hp 4cyl wont rev above 3000rpm

I had to remove flywheel cover and oil tank, starter and fuel pump. Two 7/16 nuts on each carb. Run a bungee thru the center of the oil tank and suspend it from above, so you don't have to unhook the line. It'll take most of the day if you haven't done it before.
 
C

crazyhunter

Petty Officer 2nd Class
Joined
Jan 25, 2012
Messages
128
Re: 40hp 4cyl wont rev above 3000rpm

well luckly my oil tank was removed by the preveous owner so that should save me a few minutes but it sounds like i will have a nice weekend project
 
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