1985 50HP 4-cylinder power loss

[jimmbo]

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.

Not with a 2 stroke.

 

[BWR1953]

Todays update: I removed the fuel lines from the primer bulb and they were fine. They weren't bunged up inside. Both are braided. One is brand new and fairly soft, the other is a few years old, a different brand and has a hard outer case. I was curious about that and decided to take the lines and primer back to the Merc repair guy (Doug) and get his thoughts.

I was told that both lines are good to go. Doug had thought that I'd used the cheap, soft, blue lines which easily collapse. Nope. I told him that I'd learned from him several years ago never to use the cheap lines.

After I recounted the event on 1 Jun 22, Doug said that it sounds like I need to rebuild the carbs. Fortunately, I'd ordered rebuild kits over a week ago and they're out for delivery now.

That'll be my next step.

 

[jhande]

Todays update:

Doug said that it sounds like I need to rebuild the carbs.

Humm...
Okay so Doug is addressing the running issue.
Surprised he's not concerned with the low compression reading.

 

[jhande]

Not with a 2 stroke.

 

[BWR1953]

Humm...
Okay so Doug is addressing the running issue.
Surprised he's not concerned with the low compression reading.

It was addressed in post #18.

 

[jimmbo]

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

Carbon buildup behind the Rings is Gradual, but eventually there comes a point where the Rings can no longer compress, and when that happens, bad things happen to the Rings , Ring Grooves, and or Cylinder Walls

 

[BWR1953]

Carbon buildup behind the Rings is Gradual, but eventually there comes a point where the Rings can no longer compress, and when that happens, bad things happen to the Rings , Ring Grooves, and or Cylinder Walls

Right-o. Hopefully the Power Tune we sprayed in there yesterday morning helped clean things up.

 

[jimmbo]

I hope you ran the engine at WOT under load, after letting it sit for an hour or so.

 

[BWR1953]

I hope you ran the engine at WOT under load, after letting it sit for an hour or so.

Nope, I just followed the instructions on the can, which said to let it sit for 15-30 minutes, then rev it slightly and let it run 4-5 minutes.

We let it sit for 35-40 minutes, then revved it to 1,200 - 1,500 RPM for 5 minutes or so.

Can't run it at WOT under load unless on the water, which wasn't an option.

What I found interesting while I was spraying the cleaner... the bottom carb had less effect while I was squirting. Spraying into the top carb would immediately cause the engine to bog and sputter, but it didn't seem to have much effect with the bottom carb.

As I was using up the can, especially after reaching the half full point, the effect was less sensitive, i.e. I could put more cleaner in the carb for a longer period and the engine wouldn't react as badly.

There was definitely a lot more smoke as I was spraying, compared to before I started.

This is before spraying.


And this is after the soak and restart.

 

[BWR1953]

The carb rebuild kits I ordered arrived last night. I'm dealing with a couple of other tech issues right now, but hope that I can start the rebuild in the next couple of days.

 

[jimmbo]

Back in the Day(1970s), the Procedure was spray the Stuff in there, when the can was getting close to empty, reduce the rpm a bit and Stall the Engine with an excessive amount, let it sit a couple of Hours, then go roaring down the lake, to blow the stuff out. In the 60s and 70s, OMC Engine Cleaner was a much more potent Formula, I think it was pure Carbon Tetrachloride. It really Stank, and the resulting Smoke would burn your Eyes, and Nose. It worked well though. I poured some on a badly carboned Cylinder Head. 20 minutes later, it looked like paint does when your apply those Stripping Fluids, and the Carbon just wiped off.

 

[BWR1953]

Back in the Day(1970s), the Procedure was spray the Stuff in there, when the can was getting close to empty, reduce the rpm a bit and Stall the Engine with an excessive amount, let it sit a couple of Hours, then go roaring down the lake, to blow the stuff out. In the 60s and 70s, OMC Engine Cleaner was a much more potent Formula, I think it was pure Carbon Tetrachloride. It really Stank, and the resulting Smoke would burn your Eyes, and Nose. It worked well though. I poured some on a badly carboned Cylinder Head. 20 minutes later, it looked like paint does when your apply those Stripping Fluids, and the Carbon just wiped off.

Times change, I guess.

 

[Watermann]

Lots going on here, could you pull the spark plugs, number them and take a pic? No idle change when spraying that PT could mean a couple things. Mainly thinking no fire due to a plug not firing which could mean the switch box dropped a cylinder. A spark test may be in order.

Also after I do the power tune and let the motor sit without hitting the lake a snotty black goo will drizzle out of the prop hub.

 

[BWR1953]

Lots going on here, could you pull the spark plugs, number them and take a pic? No idle change when spraying that PT could mean a couple things. Mainly thinking no fire due to a plug not firing which could mean the switch box dropped a cylinder. A spark test may be in order.

Also after I do the power tune and let the motor sit without hitting the lake a snotty black goo will drizzle out of the prop hub.

I actually started to do a spark test last week but couldn't see anything well enough in the bright sunlight and it was miserably hot too, so I didn't want to mess around out there much. The Chief is occupying the garage, so we're limited to working outdoors. It's the normal rainy season here, so we haven't been able to do the spark test in the cooler part of the evening yet. We'll get it done as soon as we can.

Meanwhile, here are the spark plug pix. They're a lot dirtier after the PT treatment. They were all essentially new before that and looked that way.

They definitely look interesting. Something going on with the bottom 2 cylinders for sure. Looking pretty rich I think.





And although the prop hub is currently clean, it looks like there was some black gunk that came out.

 

[BWR1953]

Orange y'all glad I got the spark test done this evening?

The tester is a cheap HF unit and the spark chamber shows orange when in use. I was concerned at first that the spark wasn't white, but once I got down to cylinder 4, my fears were allayed. On Cylinders #3 and #4, the rubber boot wasn't on tight enough and shorted to the engine. You can see it on Cylinder #3 in the video. On Cylinder #4, the boot was loose at the tester and was sparking bright blue-white there! (Yes, I turned the engine off before reseating the boot. )

Also, I did some more research about that tester and every video I found with the HF Tester in use showed the spark as orange in the chamber. So, I'm thinking that I have good spark overall, but I'd appreciate y'alls thoughts.

Cylinder #1


Cylinder #2

Cylinder #3


Cylinder #4

 

[jimmbo]

Can it jump a 3/8" air gap? Again, can it jump a 3/8" air gap?

 

[Sheetmetal]

Check the pick up tube in your fuel tank. The filter could plugged up or the tube could have fallen off.

 

[racerone]

Not sure I would trust those blinky testers.----Does spark jump a gap of 3/8" or more.-----Easy to make that test device with cardboard , glue and some wire.---With 70 PSI compression I would pull intake bypass covers and look at pistons / rings.-----Water pump impeller changed every 5 years or so ?------Is exhaust tuner plugged with carbon ?-----Check that out.

 

[Watermann]

I actually started to do a spark test last week but couldn't see anything well enough in the bright sunlight and it was miserably hot too, so I didn't want to mess around out there much. The Chief is occupying the garage, so we're limited to working outdoors. It's the normal rainy season here, so we haven't been able to do the spark test in the cooler part of the evening yet. We'll get it done as soon as we can.

Meanwhile, here are the spark plug pix. They're a lot dirtier after the PT treatment. They were all essentially new before that and looked that way.

They definitely look interesting. Something going on with the bottom 2 cylinders for sure. Looking pretty rich I think.

View attachment 365782

View attachment 365781

The PT application and no water run time does make it tough to read the plugs. You said that spraying the PT in the bottom carb didn't affect the idle and the 2 bottom plugs don't have the distinct light brown around the electrode. Something isn't right with the bottom 2 cylinders.

Addressing the elephant in the room, the first thing to do anyone says is run a compression check and with your compression numbers being 70 ish, I really don't know how much time and money I would exert on the motor. Personally on my old motors I have no problem sinking money into them if the numbers are above 120, I know I can get many years of use on the cheap before they start to loose their will to live.

I know the feeling is that the motor has ran really good up until now but with low compression numbers it's on borrowed time to where no amount of new parts will make it run better short of an internals rebuild.

 

[BWR1953]

Geez guys, yer killin' me over here! My wallet's in a lot of pain!

Compression: in the room. I know, right?

As for my background, I've been through a "holed piston" event. Back in the early 80s, I was on my way to work on my Suzuki GT750 "Water Buffalo" 2-stroke, 3 cylinder water cooled motorcycle when it burned a hole through the center cylinder. I ended up having to tear it down and replace the piston, then immediately traded it for a car.

It's been suggested by several on this thread, as well as by my local mechanic, to try to get a good reading from a different tester. Last week I ordered another compression tester and it'll be here tomorrow. It has very good reviews for accuracy. I'll return the cheap HF unit locally and try again with the new one after it gets here.

What perplexes me is how all four cylinders could suddenly drop 60 points not only simultaneously, but completely evenly in just a few minutes. Makes me think that the low compression readings are in error.

Spark: I just ordered another spark tester since the "blinky" one I used may give a false positive indication. The new one is a different style and should show the gap. It'll be here by the end of this week.