1985 50HP 4-cylinder power loss

[BWR1953]

On 1 Jun 22 I was on a fishing trip. The engine ran normally at startup, then cruised to the first fishing hole at 5,300 RPM WOT like it usually does. When we slowed down, the engine didn't sound right. It burbled and gurgled and made the 2-stroke ring-ding-ding sound. Hadn't heard that before. My boy even noticed and said "That doesn't sound right." as we were slowing.

We fished awhile, then got ready to move to a second spot. The engine fired right up but wouldn't accelerate normally. It barely got to 3,000 RPM and if I pushed the throttle more, the engine would bog down further. So, I just limped us back to the dock as quickly as I could get us there. I didn't do any testing, like squeezing the fuel bulb. I just wanted us to get to shore quickly.

Engine info:
1985 50 HP 4 cylinder.
S/N 6589696
Power trim & tilt
Walbro carbs

We've done a little troubleshooting and it's looking like a fuel starvation issue. Maybe? I'm not real good at troubleshooting. And I'm concerned about compression as well.

Background:
In May, we went on a fishing trip and at the dock when I squeezed the fuel primer bulb, gasoline started squirting out of the side of the bulb. Trip over!

When I replaced the bulb in May, the fuel hose ended up being short, so I just connected it up the way it was and that's how it was rigged during the issue on 1Jun22. We replaced the short section with a new 3' section last week.


During testing, the engine fired right up and idled fine. Telltale was normal.



The carb fuel filter was inspected and no debris was found and was full of gas when primed and the engine was off, but had low fuel level while running.


We completely drained and filtered the gas can and there weren't any major issues there. Just one bitsy little item.

The in-tank screen had a little bitty hole, but that was it.

 

[BWR1953]

I did a compression test last week with a borrowed compression tester and all four cylinders were at 70PSI! We tested it after warmup with and without the throttle open. No difference there.

So, I bought a new compression gauge and tested again. Same result! Then we added a couple squirts of straight 30W oil into the cylinders and test once more. Compression went up to 80PSI, but that was it.

When I got the motor in 2015, it was on a donor boat and didn't get installed onto the Kingfisher until much later. At the time of purchase, the engine had been "sitting awhile" according to the seller. But, we measured it then and it had 130PSI on the top 3 cylinders and 135 on the bottom. Spark was good, so I bought the whole shebang.

Before installation on the boat several years ago, I rebuilt both carbs, installed a new impeller and pump assembly, then vacuum and pressure tested the lower unit. All good.

In May 2020, we splashed the Kingfisher and the Merc ran great, getting the boat up to 35MPH with my wife, the boy and myself on board. It's been used on the water a couple dozen times since then, plus some testing in a barrel in the garage.

I'm so confused...

Last year I installed 4 new coils, plugs and coil wires.

The engine has been running well for us, so the compression discrepancy is really bugging me.

 

[jimmbo]

You didn't by chance forget to put Oil in the Gas?
Time to take off the Transfer Port Covers to get a look at the Rings and Piston Skirts

 

[BWR1953]

You didn't by chance forget to put Oil in the Gas?
Time to take off the Transfer Port Covers to get a look at the Rings and Piston Skirts

We were very careful to make sure that we mixed oil with the gas. We had the oil and the mixer thing with us.

How do I remove the Transfer Port Covers? I'll start searching for a video too.

 

[jimmbo]

They are on the Starboard Side of the engine, a few bolts and they come off. Once off, the Ports will be visible, allowing inspection of the Piston and Rings
Take Pictures before disassembly so you know what and where things were attached to them

 

[BWR1953]

They are on the Starboard Side of the engine, a few bolts and they come off. Once off, the Ports will be visible, allowing inspection of the Piston and Rings
Take Pictures before disassembly so you know what and where things were attached to them
View attachment 365434

Is it buried under all this stuff?

 

[BWR1953]

I just remembered that while we were filtering the fuel that I could see the oil in the mix, not just the gasoline.

 

[jimmbo]

Yup. I didn't say it was gonna easy, but you need to see if there is scoring and/or stuck Rings. There is no Cylinder Head that can be removed. I guess you could put a camera into the Spark Plug Holes to look at the walls. Take the plugs out and look at them. they often reveal clues if something mechanical had happened to the powerhead

The Switchboxshould unbolt and be moved out off the way without having to disconnect many, if any wires, same goes for the Coils. Starter might be in the way, but it too can be removed, actually the least complicated to do

I had to ask about the oil, as there are a lot of People who just pour gas in, and drive.

 

[airshot]

When was the last time you cleaned the internal engine with some sea foam or other cylinder cleaner?? Just might be stuck rings....

 

[jimmbo]

There are much better Snake Oils than SeaFoam. Power Tune(Merc) and Engine Cleaner(BRP) are good ones. CRC makes a couple that would be okay as well
You could try them before tearing things apart.

 

[BWR1953]

Yup. I didn't say it was gonna easy, but you need to see if there is scoring and/or stuck Rings. There is no Cylinder Head that can be removed. I guess you could put a camera into the Spark Plug Holes to look at the walls. Take the plugs out and look at them. they often reveal clues if something mechanical had happened to the powerhead

The Switchboxshould unbolt and be moved out off the way without having to disconnect many, if any wires, same goes for the Coils. Starter might be in the way, but it too can be removed, actually the least complicated to do

I had to ask about the oil, as there are a lot of People who just pour gas in, and drive.

I understand completely about the oil. No worries.
And yeah, my thought at first was lack of oil.
I'd thought there was no head gasket but wasn't positive.
I've had the starter off plenty of times. No biggie really. Just getting it reinstalled with the power terminal away from the cowling is interesting if not done correctly. BTDT.

When we replaced the coils, we had to move the switchbox around a little.

I guess we'll get started in the morning when I get home from the doc and the boy finishes cutting the grass.

 

[BWR1953]

When was the last time you cleaned the internal engine with some sea foam or other cylinder cleaner?? Just might be stuck rings....

Haven't done that since before the splash in May 2020.

 

[BWR1953]

There are much better Snake Oils than SeaFoam. Power Tune(Merc) and Engine Cleaner(BRP) are good ones. CRC makes a couple that would be okay as well
You could try them before tearing things apart.

I do have SeaFoam. I'll look around for Merc Power Tune.
And I just texted my buddy to see if he has a borescope.

 

[Faztbullet]

I'd say your jumping the gun and to try a different gauge one more time

 

[Dave1027]

Isn't the exhaust cover on the other side of the motor? On my motor it's next to the throttle/timing arm and nothing is blocking it.

But I agree. Before tearing into it, try the compression test again with a known good gauge.

 

[jhande]

I did a compression test last week with a borrowed compression tester and all four cylinders were at 70PSI!

So, I bought a new compression gauge and tested again. Same result! Then we added a couple squirts of straight 30W oil into the cylinders and test once more. Compression went up to 80PSI, but that was it.

When I got the motor in 2015, it measured then and had 130PSI on the top 3 cylinders and 135 on the bottom.

A 10psi increase from dry to wet shows just a minute compression loss usually do to ring to cylinder sealing.

A 60psi drop/difference when first tested is a major concern I would have. That would equate to a noticeable loss of power.

Could you of had 2 faulty compression testers? Possible if both the same cheap brand but not usually likely.

An old timer mechanic friend of mine swore by using Marvel Mystery Oil. Get the cylinders facing vertical and a few squirts in the spark plug holes used to free up piston rings. If they're really gunked up with carbon then use as recommended above. Another old trick is to spray a mist of water into the carbs while motor is running. The mist of water vaporizes and boils carbon deposits off.

 

[flyingscott]

Do another compression test and make sure your starter is turning fast enough. All plugs must be out for a compression test. If you are using the autoblend system throw it away as soon as possible.

 

[BWR1953]

Update from this morning:
I went to my Mercury repair shop, bought a can of Power Tune and talked with the owner. I explained everything that's going on and his first thought is that I could have bunged up the new fuel lines when I replaced the primer bulb. It's a very common issue. That could definitely be a possibility. The inner part of the fuel line has to be put on "just right" or it will roll up and cause a restriction. I hadn't even thought of that. He also said that I should try another compression gauge; said he has two and gets different readings from them.

I asked if I should just double check and fix and fuel line connection issues, run the Power Tune, then take it out on the water and see how it goes. His reply was a resounding "Yes!"

We did use the Power Tune, following instructions on the can. Then we disconnected the fuel line and took it into the garage. After that we went in the house to escape the heat. Tomorrow morning we'll go out and I'll examine and if necessary, correct any fuel line connection issues.

Tomorrow is a new day.

 

[BWR1953]

Do another compression test and make sure your starter is turning fast enough. All plugs must be out for a compression test. If you are using the autoblend system throw it away as soon as possible.

No autoblend system on this engine. And yes indeedy, the engine was spinning at full starting speed.

 

[BWR1953]

A 10psi increase from dry to wet shows just a minute compression loss usually do to ring to cylinder sealing.

A 60psi drop/difference when first tested is a major concern I would have. That would equate to a noticeable loss of power.

Could you of had 2 faulty compression testers? Possible if both the same cheap brand but not usually likely.

An old timer mechanic friend of mine swore by using Marvel Mystery Oil. Get the cylinders facing vertical and a few squirts in the spark plug holes used to free up piston rings. If they're really gunked up with carbon then use as recommended above. Another old trick is to spray a mist of water into the carbs while motor is running. The mist of water vaporizes and boils carbon deposits off.

I can't imagine how the rings could get gunked up when the engine has been running fine for several years. Beats me.