15hp Johnson only running on one cylinder

[fishon1213]

I have a 1981 15hp Johnson. The motor quit running due to some rodents filling the intake full of birdseed. I know, right. So I ended up having to take the powerhead off only to find several sunflower seeds stuck in the reed valves. I cleaned and reassembled that side of the motor. Then I flushed the cylinders with 50:1 mix through the spark plug holes. I was ready to give up, but then she ran. But only on one cylinder.

Clean carb, new plugs, good spark to both plugs, good compression on both cylinders. So what are some issues that could be making that bottom cylinder not fire. Lack of fuel maybe? Maybe I didn't get the reeds right. Does one set of reeds work for one cylinder or do they all work together?

 

[kbait]

Re: 15hp Johnson only running on one cylinder

Each cylinder has it's own set of leaf valves (reeds). One side may not be sealing. If you pull the plugs and turn the flywheel clockwise, you should be able to hear each set of reeds 'wheezing' once per set/per revolution.

Hope this helps..

 

[James R]

Re: 15hp Johnson only running on one cylinder

A compression test would be a good bet before anything else.

 

[OptsyEagle]

Re: 15hp Johnson only running on one cylinder

Sometimes when a leaf valve is not seating you can see fuel shooting out the carb throat. Take a look, if you see some most likely it is the leaf valves.

 

[the machinist]

Re: 15hp Johnson only running on one cylinder

It is possible when reassembing the manifold to swap the inner with the outer reed plate gaskets (they look very close to being the same). If this happens, the inner gasket may be holding one of the reeds closed.

 

[fishon1213]

Re: 15hp Johnson only running on one cylinder

Well, sounds like I have to play with the reeds again. Man they are such a pita to take off this motor. Which side of the reeds controls which cylinder?

 

[Bosunsmate]

Re: 15hp Johnson only running on one cylinder

You could ground the bottom HT wire and turn it over a few times with the plug still in there. Then see if the plug is wet with fuel.
You can also put your hand loosely over the carb throat and see if you feel any backdraft from the carbs indicating reed problem

 

[fishon1213]

Re: 15hp Johnson only running on one cylinder

Ok, worked on it a bit more today....
There is no fuel running back out the carb throat, and listening to the reeds, they seem to be working. The motor does run with a bit of throttle, but wont idle down and stay running. After running for a bit the top plug looks as it should, the bottom plug appears to be wet with fuel, indicating an excess. If I pull the top plug wire while it is running it dies immediately, if I pull the bottom plug wire it doesn't change much, but does it does run a bit rougher and eventually die, so I think the bottom cylinder is working somewhat.
What is the initial setting on the fuel mixture? Could a carb problem just flood the bottom cylinder? Any other advice?

 

[the machinist]

Re: 15hp Johnson only running on one cylinder

Sounds like you may have a bad ground on a coil or even a partial arced plug wire under the boot. Pull the lower cylinder spark plug boot stright off the wire, under it you will see a coiled wire end that slips over the spark plug end. Cut off about 3/8" off the end of this plug wire, pull the coiled wire plug connector prong out of the now cut off wire. Replace it into the "New" wire making sure the sharp prong goes into the inner metal wire. Sometimes this prong off the coiled wire may get arced inside the rubber wire casing & cause intermittant firing.

On that metal topped carb, the idle needle initial setting is usually 1 1/2 turns out from lightly bottomed out.

However this does not sound like carburetor problems. Still sounds like a reed plate gasket holding one of the dual reeds from opening. Which would only feed 1/2 of the fuel to that cylinder & if you keep running it in this condition (if that is what it is) you will have no lubrication on that cyclinder & it can gall, then blow a piston. I have seen this twice. I know, PITA to pull the manifold while the powerhead is bolted on. BUT are you willing to take the chance?