50hp mercy will not get to rpm

[Jsmyth]

I have what I think is a 1984 50hp mercury outboard 4 cyl. I can only go about 10mph in my boat but I should really be doing 25+. The engine will not reach rpm. I have checked spark, change the plugs and wires, rebuilt the carbs and adjusted the spark advance. The compression checks out too a 115psi on all 4. What am I missing? Any ideas? It's getting plentty of fuel.

 

[GA_Boater]

Welcome aboard, J.

Two things to look at, both throttle related.

Disconnect the throttle cable at the motor and make sure the carbs open completely by opening the throttle arm manually. Binds in the throttle arm and linkage to the carbs can keep the carbs from opening all the way,

If the above checks out, connect the cable and again make sure the carbs open all the way with the remote control assuming you have a remote. Throttle cables can stick and swell internally.

 

[Jsmyth]

The carbs are synced and at WOT on the remote they are fully open.

 

[Chinewalker]

Try a cylinder drop test. With insulated pliers or electricians gloves, remove one plug wire at a time and note what happens. I had an early 1980s Merc 50 in my shop a few years ago that was losing power - turns out there was a gasket leak on the intake port cover so it wouldn't draw fuel on two cylinders, even though we had spark and compression.

 

[Jsmyth]

Someone told me it might be a clogged exhaust system.... sound right?

 

[Jsmyth]

The intake gasket where? So a vacuum leak?

 

[Jsmyth]

Could I test this buy spraying starter fluid into the carbs to see which one isn't getting enough fuel?

 

[Chinewalker]

The intake gasket where? So a vacuum leak?

On the starboard side of the motor is your intake cover(s). If there's any evidence of oily seepage, that might indicate a leak.

Not likely to be an exhaust blockage.

 

[Chinewalker]

The intake gasket where? So a vacuum leak?

On the starboard side of the motor is your intake cover(s). If there's any evidence of oily seepage, that might indicate a leak.

Not likely to be an exhaust blockage.

 

[DeepCMark58A]

Could I test this buy spraying starter fluid into the carbs to see which one isn't getting enough fuel?

It is never a good idea to use starting fluid on a 2 stroke engine.