1986 Merc 115 Power Surge above 3K RPM

[griswell]

I have an 86 Merc 115 outboard on a Astroglass 16.5 Bass Boat that has been out of the water for 10 years. I began by replacing or rebuilding the following:
Stator
Bottom switch box
Starter solenoid
Spark plugs
Fuel line with prime ball
Fuel pickup tube
Fuel pump (rebuild)
Carburetor (rebuild)

Cleaned out the fuel tank, replaced with non-ethanol gas, mix 50:1
Once started I fog oiled the engine as directed on the can.
I have spark at all the plugs.
Compression high is 130 and low is 121 psi.

The engine starts and idles well. As power is applied it powers up well through 3000 RPM. Above 3000 RPM the engine surges and misses. At times it blows puffs of smoke out the exhaust. After boat comes to plane I can power back to 3K RPM and slowly apply throttle and sneak up to 3800 RPM, but that?s it. I can feel it surge slightly as it runs about 40 MPH. I do not know where to go next, any suggestions are appreciated. I can post a video if needed.

 

[Charlie61]

Re: 1986 Merc 115 Power Surge above 3K RPM

I also have a astroglass 1983 17.5 with a 115hp inline 6 . it had not run for over 8 years. I also replaced and repaired the same as you I hope you repair the water pump .I have only had mine out one time because of bad heart you may want to check enrichen vale mine sucking air . i just got service manual from tradebit. com for only $5.00 downloaded it helpful your fuel linkage may need ajusted

 

[griswell]

Re: 1986 Merc 115 Power Surge above 3K RPM

Charlie61 thanks for the link on the manual. I was hoping to find one at a local marine shop, but who can pass up $5.00 shop manual; I'll check it out. This is my first boat so I really do not know what the enrichment valve is, but I will check it out in the manual.

 

[griswell]

Re: 1986 Merc 115 Power Surge above 3K RPM

Charlie61 thanks for the link on the manual. I was hoping to find one at a local marine shop, but who can pass up $5.00 shop manual; I'll check it out. This is my first boat so I really do not know what the enrichment valve is, but I will check it out in the manual.

Oh I did repair the water pump. thanks

 

[griswell]

Re: 1986 Merc 115 Power Surge above 3K RPM

Oh I did repair the water pump. thanks

I decided to go through the carbs again by using carb soak and replaced all the fuel lines inside the engine. I took extra time setting the float valve. I noticed the enrichment system lines where they enter the engine were loose. I removed them, checked to ensure they were clean. I reinstalled them with some Teflon tape on the treads to seal the connection. After carb install, I concentrated on setting the timing. I used the directions from the service manual. I had a problem setting the advance timing screw, so I took it to the lake and adjusted it using trial and error. After a few tweaks, I was able to get the engine to power up to 4400 RPM running at 47 MPH. I was happy to finally get the engine to power up.

 

[canoemang]

Re: 1986 Merc 115 Power Surge above 3K RPM

I think 4400 is low for that motor, you may be lugging it..

maybe a pro will chime in about props etc..