'83 Johnson 25hp ignition issue

I have an '83 Johnson J25ECTD that's not firing on top cylinder. I can start the motor quite easily but it's "sneezing" at low rpm. The top plug is very wet with unburned fuel and the bottom plug is sooty but dry (plugs are new). Good spark with air gap tester, good compression (135 on both), very clean carb. I have swapped the coil positions with no change. Does this sound like a bad power pack? Does this ignition system require a battery when it's running? I removed the flywheel and cleaned the magnets with 400 grit paper (lightly) and it didn't help.

Re: '83 Johnson 25hp ignition issue

More than likely a bad fuel pump diaphragm. It has a small hole in it, letting fuel pass through into the top cylinder. You are trying to compensate for that extra fuel by leaning out the carburetor adjustment, which is only making the bottom cylinder too lean and makes it sneeze.

Remove the fuel pump from the motor, hoses still attached, and give the squeeze bulb a pump. If gas comes out the back of the fuel pump, I guessed right. If not, ....oh well, we tried.

Re: '83 Johnson 25hp ignition issue

Thanks F_R! I'll take a look at the pump.

Re: '83 Johnson 25hp ignition issue

F_R, I took the fuel pump off and tested it like you said, and sure enough, fuel squirted out from everywhere (except where it's supposed to). So..being to cheap to buy another pump, I ordered a re-build kit for the old one. Thank you for the advice.

Re: '83 Johnson 25hp ignition issue

When ever you take a fuel pump off of the block like that to test it you should get some nuts for the mounting screws, install them and tighten them down. This simulates the same thing as being on the block. Then you pump the primer bulb and check the pulse fitting on the pump that goes to the block for any leaks. Without the nuts they will leak all over. Been there.

Re: '83 Johnson 25hp ignition issue

Boobie, I didn't do that. Will check it again. Thanks Bud!

Re: '83 Johnson 25hp ignition issue

Well, I got the re-build kit (oem) and discovered that the pump on the motor is not the right one. The new gaskets and diaphragm are smaller by 1/2". So, I got the correct pump (from another omc 25 Hp) and put the kit in that one. Tested good no leaks. Put it on the motor, started it, and got the same results. Hard sneeze at low rpm, and it needs half choke to stay running. I have thoroughly cleaned and re-built the carb (twice). It seems to rev ok (bear in mind I'm running it in a barrel) but will sneeze hard when I slow it down. It doesn't seem to react to slow speed needle adjustment. I'm using one full turn out as a starting point and have gone as far as three turns with no change. Link/synch is good, ignition seems good, fresh fuel, new Champion plugs @ .030, good compression, and I peeked in at the reeds and the appear clean. I can't figure this out and sure could use some advice.

Re: '83 Johnson 25hp ignition issue

Update...Success! After the fuel pump issue, link/synch re-adjustment, removing the needle valve bearing, and many hours of frustration, the SOB is purring like my cat! Someone (armed with a screwdriver and a pair of pliers) "adjusted" this motor and left no screw unturned it seems. And now, it's 5 o'clock somewhere!

Re: '83 Johnson 25hp ignition issue

glad to hear it...seems truer all the time..if you're not the original owner it's no tellin' what you'll get into with these motors