1976 Johnson 35 hp Missfiring or sneezing

[ianferron]

From idle to mid RPM it missfire. The rpm drop and come back up and it's sound like a sneeze. It's worse when cold but still doing it when warm but not as often. Cleaned carburetor twice, change spark plug, adjust low speed mixture, cleaned points and replace condenser, try new coils, try another fuel pump I had. At high RPM the engine perform as it should I think. I seen 21-22 on the GPS today.
I wish I could get rid of that misfiring. I was thinking, maybe a crank seal or maybe I need to rebuilt my carb???

 

[scanman]

Re: 1976 Johnson 35 hp Missfiring or sneezing

IMHO It kinda sounds like the low speed orifi are still plugged. When ya had the carb off did ya remove the welch plugs & clean out those three tiny lil holes?

 

[ianferron]

Re: 1976 Johnson 35 hp Missfiring or sneezing

Can I remove that welch plug and put it back without damaging it or I need to replace it? Does it have to be air tight?

 

[ianferron]

Re: 1976 Johnson 35 hp Missfiring or sneezing

Ok I went to the local store today and bought a carburetor kit. Clean all passage and install new welch plug, gasket... I also changed fuel line while I was there. I started the motor and it started acted up again rpm dropping and comming back up. I pull the choke manually about half and seen to work better, so I turn the low speed mixture to make it more rich and seem to work better but it smoke like hell with that setting. The RPM still drop sometime but not as bad, the bottom spark plug got wet a little but the top one look fine. Would a bad crank seal would do anything like that?

 

[ultra353]

Re: 1976 Johnson 35 hp Missfiring or sneezing

Sounds like you have an air leak somewhere. When the engine is running spray wd-40 ( with the long red nozzel attached to get better aim) all along the carb, along the seam of the two crankcase halfs, reed plate area, ect. If rpms increase when one of these areas is sprayed you`ve found an air leak.

 

[2dbit]

Re: 1976 Johnson 35 hp Missfiring or sneezing

I am interested in this as well. Cleaning the carb did nothing for me, this includes complete tear down and dip. Now, I am in the middle of a rebuild on my Merc 18hp, mine would sneeze as well...intermittently at idle. Ran like a top at all other speeds. http://forums.iboats.com/showthread.php?t=503839 take a look at the second set of pictures, I wonder if the displaced reed block seal was causing it, or if the reeds being bent out of limits (not by much, .002-.003"). Never mind all the piston/cylinder damage, that was a more recent development (lets not get into it)