Why is my motor missing? Video

[MrSimon]

I have a 20HP 2 stroke 1987 Mercury that seems to be missing.

Any ideas? You can hear it missing in the video.

https://youtube.com/watch?v=71M2yAl1m_I

 

[Weldorthemagnificent]

I don’t know but I like how it pees a little out the front when it farts. Lol. I watched it twice. I have a 35 Johnson that does that when it’s cold especially if it hasn’t ran a while. When the motor warms up it smooths right out. Hose water be pretty cold this time of year unless you’re southern in which case you’d just chew some tobaccy and go fishin. You can try it in a garbage can full of water and let it warm up. I swear by seafoam in the gas. I add some to the first tank every year.


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[water bouy]

No biggie, it won't push that 4 wheeler very far anyhow.

 

[nccatfisher]

It is dropping out on one cylinder periodically, common for those smaller two cylinder motors. Could be a myriad of things. What have you done to it so far?

 

[Shaugh]

Your first guess on a miss like that would be a bad condenser or coil pack...

 

[Pappy]

There were no condensers in 1987.......Total electronic ignition.

Anyway. Three things to look at here.
The engine is trimmed up. This alone will lean the mixture at idle.
The engine is out of the water, back pressure is reduced, and again leans the engine somewhat.
The mixture itself may be lean at idle.
A fourth. Lack of a thermostat. Thermostats were designed to warm the engine at idle and increase idle quality as a result.

 

[MrSimon]

My plan is:

New gas with just the right mix
New spark plugs
New ignition coils
New plug wires

Parts are on order. I'll report back when I put them in.

The motor currently has a new fuel filter, a good clean carb, good fuel lines, new impeller .... and seems to run strong except for the miss.

 

[Shaugh]

I agree with Pappy. You should do your test over again. Put the engine in a barrel of water so you'll have correct back pressure. Make sure the motor is level. Run it that way and see if it still misses... Those muffs are a poor way to evaluate an engine.

 

[MrSimon]

I'll try that.

 

[Tinny Fleet]

Sounds pretty good to me. Before investing a lot of $ I'd just run it, and let it warm up under load. Like one of the first posters said, it should smooth right out. And if you are using gas that's more then 3 months old dump it for fresh!!! And if you want to get rid of a lot of the smoke, get synthetic opil. Between just those two things a lot of noise, smell and smoke will go away!!!

 

[MrSimon]

Back pressure was the ticket.

I put some fresh gas in, dropped it level, and used a barrel instead of muffs. Runs great.

I put the muffs back on to see if maybe it was just the gas. Nope. It immediately started missing on the muffs.

https://youtube.com/watch?v=p46NX-eOi4E

 

[Shaugh]

That's why Pappy gets the big bucks...