1980s mercury 115 tower of power issues!

[Jonboy123]

Bought a boat from my ladies parents and it's given me problems since the beginning. At first it ran great the first time out. Had a hard time getting enough power to plane out. Then after warming up dropped in speed at WOT and started running horribly. Took it to a local mercury mechanic said he ran through it replaced impeller and tried to adjust the carbs. Ran worse than when I took it in. So I tried cleaning out the carbs, checked compression and adjusted the carbs under load and it ran amazing for about 10 mins. It dropped about half speed. I shut it off and it wouldn't start back up. Adjusted the carbs on the water and barely got it to go 1/3rd of throttle. Took it to the nearest mechanic. They diagnosed a bad seal inside the engine which creates suction to make the diaphragm fuel pump work. Advised I could put an inline fuel pump in. Put said fuel pump in and now I can only get it to idle and dies as soon as I give over 1/3rd throttle. I took off at 1/3rd and slowly adjusted carbs as I gave it more gas got up to WOT but as soon as I go to idle it won't run right till I readjust down and start process over again. I've added a new fuel line with primer bulb. I really like the engine so I'm hoping I can figure this out! Any recommendations I'd be willing to try!

 

[jimmbo]

Welcome to iboats

There is an Old Adage, Never buy something from someone you know

What year is it? 4 or 6 Cylinder? Post a pic, that can give a few of us an idea of it's age.
First let's start with a Compression Test, post the numbers
Next verify that the Ignition can send a Spark to each Cylinder that can jump a 3/8" gap. Depending on the Year, and hence Ignition System, Heat can cause problems, from individual Cylinders losing Spark to all losing it.
Spark Plugs can often tell a lot as to what is going on. Examine them for clues.
Is the Fuel System free from Leaks, mainly Air getting in. Are the Fuel Filter(s)/Strainer(s) Clean, and that also includes the screen on the the Pickup tube in the Tank?
If you used old Fuel, how old was it?
You are mixing TCW-3 Oil in at 50:1?
If the Gasket that enables the Fuel Pump was leaking, was it fixed? If not then that Crankcase Chamber is sucking Air resulting in a Lean Mixture to that Cylinder.

This Inline Fuel Pump. Is it a USCG approved Pump. or is it some Automotive pump? If the latter, you have made your boat less safe, plus broke a few Laws

 

[Jonboy123]

Welcome to iboats

There is an Old Adage, Never buy something from someone you know

What year is it? 4 or 6 Cylinder? Post a pic, that can give a few of us an idea of it's age.
First let's start with a Compression Test, post the numbers
Next verify that the Ignition can send a Spark to each Cylinder that can jump a 3/8" gap. Depending on the Year, and hence Ignition System, Heat can cause problems, from individual Cylinders losing Spark to all losing it.
Spark Plugs can often tell a lot as to what is going on. Examine them for clues.
Is the Fuel System free from Leaks, mainly Air getting in. Are the Fuel Filter(s)/Strainer(s) Clean, and that also includes the screen on the the Pickup tube in the Tank?
If you used old Fuel, how old was it?
You are mixing TCW-3 Oil in at 50:1?
If the Gasket that enables the Fuel Pump was leaking, was it fixed? If not then that Crankcase Chamber is sucking Air resulting in a Lean Mixture to that Cylinder.

This Inline Fuel Pump. Is it a USCG approved Pump. or is it some Automotive pump? If the latter, you have made your boat less safe, plus broke a few Laws

I believe it's a 1985 I will try to get some photos in the morning but it's an inline 6 cylinder. Every cylinder had 120 on cold start but I should probably test it after it's hot. I will check the spark. The first mechanic said he tested it all but he also said these engines tend to have electrical issues. When I checked the plugs they were sooty but nothing baked on. I was surprised at how clean they were and thought mayb they possibly just changed them. Not 100% sure on air leaks in the fuel system, it's my first boat so I've been learning how to check all this stuff. Fuel filter is clean but haven't checked the one in the tank. It has alot of fuel pressure it seems but I know that could change if it vacuumed. I've been using Lucas 2stroke marine oil at 50:1 and have added some seafoam with a full tank. The gaskets on the fuel pump were in really good shape so I didn't change any except the one that is closest to the engine. But wasn't sure if when I added the new inline fuel pump if I needed to plug off the old diaphragm pump.

 

[Jonboy123]

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[Jonboy123]

View attachment 20220816_015737.jpg

 

[Jonboy123]

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[jimmbo]

The Decal is post 85, could be 86, 87, 88. Serial # would determine which
I doubt that pump is USCG Legal. It might produce too much Fuel Pressure and that is Overloading the Floats and Flooding them.
Poor location for Pump, places fuel hoses/wires near the Shift and Throttle Linkages
Switchboxes don't look like OEM, they look like the One Season Wonders from Amazon/Ebay

I had an 84, had it for 14 yrs. Put about 1200 hours it. It still had the Factory Spark Plugs when I traded it in, in 98.

In July 87, I was replacing the Water Jacket Cover as it was warped, and leaking Water from around the Sparkplugs

 

[Dave1027]

The fuel in the fuel filter does not look good. Does not even look like it has any TCW-3 in it.

 

[Jonboy123]

The fuel is brand new non ethanol gas. I personally added the oil at 50:1

 

[Dave1027]

My mistake. It's just that TCW-3 is normally grayish blue.

 

[Jonboy123]

The Decal is post 85, could be 86, 87, 88. Serial # would determine which
I doubt that pump is USCG Legal. It might produce too much Fuel Pressure and that is Overloading the Floats and Flooding them.
Poor location for Pump, places fuel hoses/wires near the Shift and Throttle Linkages
Switchboxes don't look like OEM, they look like the One Season Wonders from Amazon/Ebay

I had an 84, had it for 14 yrs. Put about 1200 hours it. It still had the Factory Spark Plugs when I traded it in, in 98.

In July 87, I was replacing the Water Jacket Cover as it was warped, and leaking Water from around the Sparkplugs

View attachment 368092

I had planned on buying a better fuel pump but didn't want to spend 200+$ if it wasn't gonna fix the issue. I had ziptied it so it doesn't interfere with any moving parts but I tried to also keep it where the existing fuel pump was.

 

[jimmbo]

Are you mixing the oil yourself, or does your engine have one of those Autoblend oil premixers?

 

[Jonboy123]

Mixing myself. I try to stick to an even gallon amount so I can get it pretty precise. And I use only non ethanol fuel.

 

[jimmbo]

16 ozs to 6 US gallons or 500ml to 25 liters, is precise enough

 

[Jonboy123]

Ya I bought a mixing container that tells you every ratio it's really convenient

 

[jimmbo]

Measuring is on thing, mixing is another part that people neglect. They just pour the oil in and think that it magically mixes. It mostly settles at the bottom of the tank. Some stirring/agitation is required, easier to do before all the tank is full. Permanent tanks require a bit more Diligence to insure a consistent mix, but Premixing the Oil in a few Gallons of gas and adding it as the the tank is being filled will help.

 

[Jonboy123]

Measuring is on thing, mixing is another part that people neglect. They just pour the oil in and think that it magically mixes. It mostly settles at the bottom of the tank. Some stirring/agitation is required, easier to do before all the tank is full. Permanent tanks require a bit more Diligence to insure a consistent mix, but Premixing the Oil in a few Gallons of gas and adding it as the the tank is being filled will help.

I usually add the oil before I put in the gas to allow it to mix it up real good then our lake is about an hr away so I'll sway the trailer back and forth to slosh it around really good. I just checked the old disconnected fuel pump and it had been sucking air could this created a bad air/fuel mixture?

 

[jimmbo]

While putting the oil in first is better than pouring it into a filled tank, swaying the trailer really doesn't do anything. If the oil is at the bottom, it will stay at the bottom. Best way is to mix in 6 gallon lots. Put in a gallon or two, add the oil, shake it, add more gas, shake again, then fill. When poured into the Fuel tank, the turbulence should result in fairly mixed batch
If the old pump, has a Ruptured Diaphragm or the gasket between the Pump and the Block is leaking, it would result in a leaned out mix in the Crankcase for the cylinder(s) involved. I believe that the original Pump used two Crankcases, to operate, one for the Pump, a Second to control a Dampening Chamber.
Why didn't you just repair the Original Pump? They are quite easy to take apart, and very simple.

 

[Jonboy123]

I did rebuild the original pump but the last mechanic I took it to said the diagnosis was a bad "slip ring" I think he said whatever creates the vacuum was worn out and not running properly and he professionally recommended I didn't add an electric pump but unprofessionally said it was about my only option if I wanted to use the motor

 

[racerone]

Fuel pumps operate with a + PRESSURE pulse.-----Would your mechanic be referring to a " labarynth " seal?-----Or perhaps bottom crankshaft seals ?