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60HP Merc 3cyl - lower cyl. not running?

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Pete_from_NC

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Men,

I ask for your help because I know little about 2cyl boat engines. I have a 1992 Merc 3cyl, 60hp. Was running great, then intermittently lost power @ 4500rpm. When I slowed down for a little bit, then opened throttle the "power" (it's only 60) came back. This pattern I was able to repeat a few times. Now it seems that power isn't coming back, motor will only go to 3k RPM.

I took it into the garage, warmed it up, and felt that the lower spark plug was not nearly as warm as the top two. Then I compression checked all 3 cylinders, and they were all just about exactly 70psi (sounds low). Checked spark on the "dead" cylinder and it looked nice and blue. All plugs look just about exactly the same, they all look good to me, a little bit wet, with very little carbon.

I'm going to take out the fuel filter and check it, I did pump fuel into a cup to check for water - didn't see any but there was a lot of debris.

Do you guys think 70psi on 3/3 cylinders means the motor needs rebuild? Or I might have a clogged carb?

Thanks

Pete
 
Carbs don't have a part in compression. Your motor needs to have fairly uniform compression on all cylinders. You also may be using an inaccurate gauge. Borrow a gauge from Auto Zone and try again. Sounds like the carbs and the tank and the rest of the fuel system needs an overhaul.
 
Thanks for the help man. Yes, I thought that maybe my gauge was not good (harbor freight), because all cylinders measured 70/70/70, and the top 2 cylinders were starting/running well, yet bottom cylinder stayed "cold".

I will get another set of readings from another compression gauge and report back.

Thanks

Pete
 
Pete-Check the spark on the cylinders also. You may have an electrical issue also. That bottom cylinder should spark as well as the other two. If it doesn't try switching a coil from it with another if you have a multi coil system. (Otherwise just try plug wires)
 
Good news: with the autozone compression gage all 3 cylinders read 100/100/100psi give or take a few psi. Harbor Freight was only 30% off...

Spark on bottom cylinder looked about the same as the other ones, good healthy blue spark.

It's also possible that I have some water in the carb, since this boat stays at my dock (covered), maybe some water got in a bad spot somewhere. I will dig deeper and take out the fuel filter and see if I can drain some fuel from the carbs to see if there's water in it. Also I picked up some sea-foam - 25 years is a long time for carbon to build up...


Thanks guys for the suggestions.

Pete
 
Men,

Thanks for your guy's help. With 100/100/100 compression on all cylinders, I took off the carbs and opened the bowl. I saw no water in this carb bowl, but there were quite a few black plastic looking specs that do not look good. I will clean all carbs and re-assemble.

Also, after taking off the top plate of this carb, I did see some water droplets. I don't know what this little chamber is for, but do you guys think these water drops = bad? I will try to attach a pic.
top of carb.JPG
Thanks!

Pete
 
The debris you mentioned and the water is not good, of course. I hope you are using non ethanol gasoline. Start at the source of the fuel supply (tanks) and take them apart and clean them. Then go to the hoe and bulb and the fuel lines going into the pump. Check and replace and tighten anything suspect. After all of that is done. Reclean the carbs and check out every little tiny orifice and clean it with compressed air. Make sure the floats in the carbs are set correctly and try a test run. I have no idea what the carb jets should be set at on your motor, but that is very important. Get a good oem manual for your motor. Report back.
 
Men,

An update: Yesterday I finished taking off all carbs, cleaning with gum-out, drained and removed gas tank, flushed with 100% gas, left in the sun to dry the last bit of gas and water. Put the tank back in, fill with 100% gas, flush the fuel lines out by priming into a bucket. Assembled everything and make sure engine starts. It started right away, less cranking req'd than normal.

After dropping the boat in the water for a test run, the engine was able to start without high-idle, which is not normal for this engine (usually requires high idle). I thought that was a good thing...then on the test run, I still am lacking power and the boat is hovering at 3500-4000rpm, should be 5500 at WOT. A few times at WOT I heard/felt that bottom cylinder kick in, but only for 1/2s or so. I did not run the boat much at all, pulled it out of the water.

I took a couple pictures - one of the spark plugs next to eachother. The "dead" plug looks very wet to me, maybe flooded? Also the throttle valve on the "engine" side of the carbs look different on the "dead" carb. It's much cleaner.

Any ideas? Maybe switch to a hotter/colder plug? Or I didn't get the "dead" carb cleaned enough? Or float in that carb is sticking open - leading to flood?

Thanks guys. Pics attached. Left plug is the wet/dead one.Plugs - L one is dead.jpg


Pete
 
Another update:

With the boat out of the water, I started the engine to feel the plug temps as it warmed up (to check which cylinders are firing). Engine started great w/ no high-idle needed. At idle, all plug temps were getting hot, as opposed to earlier when only the top 2 cylinders were getting hot. This would explain the improved starting...it now looks like I'm running 3/3 at idle but only 2/3 at WOT. I'm thinking that maybe I didn't get all ports cleaned on the bottom carb?

Thanks

Pete
 
Start motor and run at idle.-------Pull off one plug wire at a time.-----Post results of that test.------And does spark jump a gap of 3/8" on all 3 leads.------That # 2 plug, why does porcelin appear to be new looking ?
 
Plug Pull-off test @ idle:

This was a great recommendation, thanks! I was a little scared of getting shocked, but it didn't happen...

Top plug: Pull-off wire - no change in idle speed. Put wire back on, idle picks up for a second (cylinder fires), then cylinder dies again.
Middle plug: Pull off wire - engine speed drops and nearly stalls.
Bottom plug: Pull off wire - engine speed drops and nearly stalls.

Tried swapping middle to top plug (to see if it's a bad plug), but same results.

Regarding spark on top cylinder: I did run the plug outside of the engine and spark looked blue and strong. Tried to do the 3/8 gap test, but the rubber is so deep on the plug wire that I could see no spark until the rubber obscured my view.

I misled myself and you guys by saying the bottom cylinder is dead (based on temp). It seems that the top cylinder is now not getting enough fuel/spark. I may have to take all the carbs off again and really focus on top carb.

Thanks

Pete
 
Have to ask-----How long have you owned this motor ?--------Has water pump been maintained ?---------Have you done a compression test on it ?--------Anybody around that can inspect for a cylinder sleeve " out of position " on it ?---------Carburetor " trouble " usually turns out to be something else !!
 
I've owned the boat for 3 years. Compression on my neighbor's gage = 70/70/70, didn't seem right so autozone gage was used 100/100/100. I never changed the water pump, probably should have. FWIW, the "pee stream" is still strong at idle. If I get this boat running right again, for sure I will change the water pump after this summer.

Cylinder sleeve - I can take it into the boat shop that is close, but I want to try everything myself because I'm very cheap. The next thing I will try is running the boat and feeding the top carb w/ carb-cleaner to see if that cylinder takes off. If the top cylinder runs w/ carb-cleaner then I can be fairly sure I have a lean/clogged carb.

Thanks guys

Pete
 
You might try running the motor (cowl off) in the dark and check for arcing from that top plug and wire. Then a good redo and float level adjustment on the top carb. That's all I can help with considering my limited knowledge. Remember when fishing was your favorite hobby and now it is boat motor mechanics? Me too!
 
I re-cleaned the top carb, assembled, tested, and top cylinder still is not working right.

Only interesting thing - when I pull the plug wire, then put it back on during idle, the cylinder fires maybe 2 times and idle picks up and immediately drops.

I maybe will try another in the water test and adjust the mixture screw both ways to see if i'm too lean or rich.
 
Update - Good news! Leaned out the top cylinder 3/4 of a turn during idle running and the cylinder started firing again, idle speed increased. Test ran the boat, and it's back running well at WOT! I have no idea why I needed to adjust this though...

Maybe I do need new plugs, and with new plugs I will try to richen (word?) the mixture and see if it runs good. I am aware that lean can be bad...

Also when I pull the boat this summer I will for sure change the water pump impeller. Thanks guys for all your help.

Pete
 
Great Pete. Do yourself a big favor and check the oil in the lower unit. Just take the lower plug out and see if the oil looks like a milkshake. That has a lot to do with seals on your motor and some mono wrapped on your prop shaft will wreck a seal in no time.
 
Update: the boat started acting up again in the same fashion, only going to 3,000 RPM. I pulled the boat and checked spark on all cylinders - this time bottom cylinder had no spark. After ruling out coils, I bought and installed a new powerpack and things are good again.

The powerpack was the problem all along. Seems that when it cooled down, it worked, but after the motor got warm spark would drop from bottom cylinder. I'm just posting this in case anyone else has similar issues maybe it will help them.
 
Thank you! The switch box on my triple may also be doing this. It runs fine for a 1/2 hour, then screws up so bad it won't staying running.

Jeff
 
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