Strange idle/running issue on Mercy 60hp 2 stroke

[sutor623]

Hey guys, been working on a new to me Merc 60 hp (45 Jet) serial OG211795. It is a 3 cylinder, pretty sure 49 cu in.

Here is the issue. The motor is a bit hard starting, and will run on the muffs down to a slow idle. To the trained ear, it sounds like it is (intermittently) not firing on all three cylinders. It is erratic when you first start it at a high idle, then will settle down when you back off the throttle. In the water it will not idle down and will just cut off when you back off throttle. (Keep in mind this is a jet and it always has a load on the motor when in the water.)

Compression is 110 psi across the board. Got spark on all three cylinders. Indexed the flywheel and all cylinders are firing in the proper order.

I did the drop cylinder test and it is not reacting to cylinder 2, so that is the cylinder I believe we are having issues with. I swapped the ignition coil and no change. I am running fresh wires to all 3 cylinders.

Trigger checks out good, with proper firing order, good resistance numbers, no short to ground, and good cranking DVA. Stator has two wires, one red and one blue. The red wire has proper resistance and cranking DVA. The blue wire, for some reason has proper DVA, but when I check the resistance the number goes to 1500ohms and then just drops back off to 1. The circuit is not reading open. This seems strange, no?

Other odd issue that I noticed, is when I checked DVA of the switchbox (connected to the ignition coils like suggested in the CDI guide) is supposed to be 150V going to 300-400V (DVA) and the readings I am getting are erratic and all across the board (spiking up to 1500V)

Guy I bought the motor from (a dealer) claims to have rebuilt the carburetors but I am not sure if he actually did. Not that he is a liar, but I have heard he is not the most thorough of guys..............

With my experience with electrical systems it would seem to me that the switchbox is being erratic (which wouldnt surprise me as it is typically the first ignition part to fail on these motors.)

 

[ondarvr]

Even if he cleaned the carbs yesterday it doesn't mean they're clean today. Clean them again.

 

[sutor623]

I hear that!! I just don't want to invest too much into this thing if the internals end up being the culprit. I was going to pull the head off and inspect the cylinder walls for damage, but these motors dont have a cylinder head!!! The block is just two pieces and I don't think there is a way to check anything out short of a teardown!!

 

[ondarvr]

I don't always replace parts in the carb when I clean them, I don't even change gaskets most of time, so unless you damage a gasket the cost is zero.

 

[sutor623]

Gotcha. Yea cheap insurance for sure.

I went ahead and took all of the carbs off, as well as fuel filter, fuel lines, fuel pump and oil injector pump and lines. I am going to replace all the gaskets and hoses while I'm in there.

Through all this I think I may have found my issue. The seller said that when the motor was setting he found oil in the lower casing, so he took off the injector pump and replaced the o ring. I always premix my fuel before I confirm the oil pump is functioning, and luckily I did this because the oil pump was loose. The bottom screw had worked its way out (which is very difficult to get to) so I am pretty sure that had something to do with the terrible idle, but I don't know.

We run these jets in remote rivers miles
From the docks, so I need to make
Sure this thing has as little chance of leaving me stranded as possible.

 

[g0nef1sshn]

unless i missed it.. you check/change out the spark plugs?

 

[ondarvr]

I had one of those motors with a jet on a 16' G3, it was a great combo, the motor got zero attention and stay tied to my dock year round, always started right up and ran great.

 

[sutor623]

Gone Fishin I have new plugs but haven't tried them yet. Never had a plug act this funny before.

Ondarvr looks like you had a tiller steer. I had a nice 20 jet on my 16'er that was a tiller, then I got this remote control motor so I can put a console up front. Hard to navigate rocks from the back!

 

[sutor623]

ONe other thing, the oil injection on this engine has the metal drive gear, should I just leave it hooked up or premix? I have premixed every other 2 stroke I have ever owned and am not opposed to ditching the oil injection on this motor.

 

[sutor623]

Got the carbs torn down and cleaned up with all new gaskets. They looked pretty clean, so I am hesitant to believe that they were the culprits.

But here is the funny thing. The guy who cleaned em hadn't siphoned the oil tank and there was some water in there. He also left the old dirty fuel filter on there. Some people just don't make any sense to me......

 

[Faztbullet]

These models are bad about sleeves turning and sliding rear-ward if overheated....

 

[sutor623]

These models are bad about sleeves turning and sliding rear-ward if overheated....

Yikes! I certainly have seen that happen before. Sucks that I can't just pull a head to take a look.

I guess the symptoms of that would be bad idle? Does the motor still tend to have good compression when the sleeves turn and drop?

Doesn't look like these things are too complicated to rebuild

 

[racerone]

Have a 3 cylinder Johnson 70 hp with one turned sleeve,------Still has excellent compression , all 3 the same.

 

[sutor623]

Have a 3 cylinder Johnson 70 hp with one turned sleeve,------Still has excellent compression , all 3 the same.

That's what I was afraid of. How does it run? Yea m good guessing hard to start and poor idle? Which cylinder is spun?

 

[sutor623]

Ok guys so I went ahead and rented a borescope
From a nearby shop to rule out cylinder issues. The sleeves are not rotated or dropped, so I am very pleased to see that. There is some slight scuffing on the exhaust side ( big surprise for 15 year old motor) but nothing I can't live with for now. Actually all in all the cylinder walls and piston heads look very good.

Now I guess I will fire her up after I do a link n sync and see what happens. I have hope that the issue has been resolved!!

And trust me I know what a turned sleeve looks like! This motor had 135psi in all 4 cylinders and I chased my tail for weeks until I finally pulled the heads to uncover this. I actually bought a reman powerhead because the shop wanted more than I wanted to spend to re-sleeve two cylinders on this block. This thing had overheated the starboard head so badly that it melted the thermostat grommet/poppet assembly.

 

[sutor623]

How that top cylinder got 135psi of compression and 6% leakdown, I will NEVER UNDERSTAND!!!

Anyways, got another one for you guys. Like I said earlier, I put a bore scope to this Mercury, and I didnt see any signs of turned or dropped cylinder sleeves. They all looked to be in the exact same location as one another. There was some scuffing on the cylinders, and as usual the top one was the worst. Didn't see any deep gouging.

So my compression at 6 cranks comes up to 110 psi on all three cylinders. (Merc manual states 15% difference is tolerable, but does not mention exact numbers) I then did a wet compression test. I tilted the motor until it was almost horizontal, squirted each cylinder with some oil, and re-checked compression, and all three cylinders came up to 120lbs. Is a 9% difference between wet and dry compression tolerable?

 

[sutor623]

Ok, update if anyone was curious to know.

I believe the combination of a dirty fuel filter, air leaking into the crankcase of cylinder 3 (oil injector pump) dirty plugs and poorly adjusted carburetors was the issue.

I started this motor up with all carbs sent out 1.5 turns (per manual) on a 20 degree day. Was very hard to start and backfiring. Didn't Idle well at all. So, with the engine running, I backed each screw out another 1/4 turn and VOILA. Now she's running perfectly. I think the cold dense air was cause for me to richen up the idle air mixture some.

Did the drop cylinder test and all three cylinders made a difference. Got this one hammered out!!