72 50hp Johnson cylinder seems to be running on one cylinder

[robtown]

I have a 72 Johnson 50hp that I can't get to idle.

In the last three years its had a new power pack, a new timer base, new coils, a fuel pump and 3 carb rebuilds.

It runs with no knocking on muffs with the start lever advanced a little.

And we've even had a couple summers of running around and pulling the innertube and such, but it's just never idled well.

I decided to chase down why this year.

This morning I was poking around and I realized that if I unplugged the #2 cylinder it made no difference, it ran just the way it always has.

Can't unplug #1, it won't run.

I haven't got my hands on a compression tester yet, but stopping the cylinders with my thumb feels "similar" on both cylinders.

I've swapped coils and tested spark to make sure I was getting fire to both cylinders.

Why would #2 not be firing if it has decent Compression and spark, and a clean carb that appears to be working correctly? Reed valve?

 

[robtown]

Re: 72 50hp Johnson cylinder seems to be running on one cylinder

Update.

I tried unplugging cylinder #1 and starting it.

It cranks and sounds about the same as if I cranked it with just cylinder #1, but it only runs for about 2 seconds and quits.

I swapped the sensor inputs from the timer base to the power pack and swapped plug wires, same thing.

I put it all back together and cranked it with both cylinders hooked up by jumping the starter so I could watch it.

It cranked perfectly, and after about two seconds it started arcing from under the boot to the plug base on cylinder #2 (about the same time span as it'll run on cylinder #2 alone). Keep in mind I've already swapped coils and wires around to make sure I didn't have a bad coil.

It seems to have some sort of electrical problem that causes #2 to not fire after running for one or two seconds, but there's still power going to the #2 plug...

Anybody?

 

[robtown]

Re: 72 50hp Johnson cylinder seems to be running on one cylinder

Solved the spark issue. It's running pretty smooth on the muffs.

Still need to get her wet and make my final adjustments...

I had the bottom carb idle screw out 1-1/8 turns since I just did carb kits, it was flooding the number 2 cylinder.

I lightly reseated it and backed it out 5/8 of a turn as per my manual and viola, two cylinders firing and no arcing!!!

I love this place...

A manual is a must have, but 20 minutes of searching will find you an answer to most any issue you come across.

 

[derail]

Re: 72 50hp Johnson cylinder seems to be running on one cylinder

Im having the same problem with my 72 50hp Seahorse. I put a set of new plugs in the top looks used while the bottom looks like it just came out of the box? i all so can hold my hand over the bottom carb mouth and the motor idles up. I think I may have a vacum leak!