1988 mariner 75 one cylinder not working

[thephoneman]

Hello folks I come with a where to start question. 1988 mariner 75hp 3cyl with power trim. Noticed my motor was shaking a little more than normal at low speed (2000-2500 rpm). After a bunch of diagnostics in having issues with the top cylinder. I ran a spark tester and had spark, but when I did the drop test I had no notable issue with that but did with the other 2. I switched plugs and still have the same issue. I plan on rechecking the spark and the power pack to ensure it's firing. Also checked compression and they are all in the 120 psi range. I know that if the coil pack is bad to replace, but if it's good where do I go from there? Any input is appreciated. Thanks!

 

[Chris1956]

Inspect the spark plugs. If one is real clean, you may be getting water in that cylinder. Also, which cylinder drives the fuel pump? If the fuel pump diaphragm leaks, raw fuel can foul the cylinder.

If you have spark, the coil pack is good, no?

 

[thephoneman]

Inspect the spark plugs. If one is real clean, you may be getting water in that cylinder. Also, which cylinder drives the fuel pump? If the fuel pump diaphragm leaks, raw fuel can foul the cylinder.

If you have spark, the coil pack is good, no?

I'll have to consult the manual about the main cylinder. I'm going to do some more tests on the coil today to make sure it's good.

 

[jimmbo]

Pull the flywheel and see if there is oil around the area of the Upper Crankshaft Seal. If oil is getting out, air is getting in and out as well.

 

[thephoneman]

I'm going to do the spray carb cleaner or starting fluid in the suspect carb first. Hoping I don't have to dig too deep to figure it out

 

[racerone]

It is rare but a cylinder sleeve may have rotated.----Pulling the exhaust covers my help inspect for that.----Gaskets are cheap.

 

[Chris1956]

Did you even look at the spark plugs? They can tell you a lot more than spraying ether into a carb.

If you do use ether, have a fire extinguisher at your fingertips. If the motor catches fire and you use the extinguisher, the powder is real corrosive, and can get sucked into the cylinders. You will then know the cause for a poor or non-running motor.

 

[racerone]

Simple inspection will find the issue.

 

[jimmbo]

Ether, just about Guaranteed to wreck a 2 Stroke

 

[thephoneman]

Appears to have been a bad coil pack. Replaced all 3 just to be safe. Water trial coming soon. Thanks for the input and patience.