johnson outboard misfire

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I've had this boat for 10 years and it's always had a slight misfire when you pull it out of gear. I'm not sure if maybe one carb is set a little lean. I pulled the plugs and the top left cylinder had the cleanest looking plug. Anyways, this outboard had four carburetors on it. It's a 1991 model and I can usually fix this problem by spraying carb cleaner into the hi and low speed jets of each carb. I did this and took it out a week later and it didn't misfire once the entire two hours I was out. Then I took it out a few weeks later and it was doing the same thing. It would misfire anytime it was under 1400rpm, but this time it was to the point where it was running so lean it would barely staying running to idle down enough to make it to the dock. Did the carb just happen to suck up another piece of dirt in the jet or something? I don't get it. The last 3 times I've flushed out those jets in the past 5 or 6 years it's always run great for at least the rest of the season.
 

motor_oil_madman

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Just to clarify most times it's not bad enough to matter, but sometimes it does it bad enough where it will misfire enough at idle to just flat out stall and it will continue to misfire in gear up to about 1350rpm. I do believe this is a looper motor JV140TLEID if I remember is the model number.
 
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Does your motor have a ignition interrupt setup on it? Where it momentarily opens the power to the coil when your putting it in, or out of gear. If you do, that switch might be corroded or gummed up. That might be whats making it run snotty.,,,
 

motor_oil_madman

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Originally Posted By: BigCahuna
Does your motor have a ignition interrupt setup on it? Where it momentarily opens the power to the coil when your putting it in, or out of gear. If you do, that switch might be corroded or gummed up. That might be whats making it run snotty.,,,
I don't think it does it will slam into gear if you let it. I always choke the motor so the rpms are down enough to put it into gear. Or course once it's warmed up you don't have to do that.
 

motor_oil_madman

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I just got done spraying about half a can of berryman carb cleaner thru all the jets and it seemed to run better from what it sounded like on the muffs. Although it didn't warm up enough to idle down, which is normally when it does it. It smoked like [censored] so that's a good sign. Maybe the last time I did it I just wasn't thorough enough. If it doesn't work i'll just have the carb rebuilt.
 
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Are you taking the carbs off the engine, taking the bowls off and spraying through the actual jets? That's the only effective way to clean them. Just spraying through the air venturi usually doesn't do much if anything.
 

motor_oil_madman

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Originally Posted By: mk378
Are you taking the carbs off the engine, taking the bowls off and spraying through the actual jets? That's the only effective way to clean them. Just spraying through the air venturi usually doesn't do much if anything.
I take spray them through the throat of the carbs. It worked great. Took the boat out yesterday. Only had a slight misfire in neutral which it's always had for 10 years.
 
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You got a 25 year old motor... carbs never been properly cleaned my guess.. video on you tube how to do yourself... my first thought was battery... not enough juice low rpms... check for any corroded connections... loose... omc used to have a decarbing tuner spray... some motors has a fitting to hook up.. not a 91 though..... just gave away my last can... I would use ETH free gas only and solid shot of seafoam every tank... check fuel filter frequently... Spray can a bandaifix till you get stuck on the water... You live in Texas... could this be some type of heat soak?? I had problems with heats oak on omc big time... Sounds like a cool motor... keep it running!!
 

JTK

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I'm wondering if one of the ignition coils is acting wonky once the heat moves things around. I've seen that and had it happen on old twin cyl outboards. I don't know that I've ever had a carb issue on an outboard that was intermittent. They either worked or they didn't.
 
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When in doubt, increase idle speed... op mentioned slamming in gear...possible shift interrupt problem... coils might be ending life soon... Evinrude boards at bass boat central good source of info...
 
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Try a different oil. My previous boat had a 4 cyl. Johnson (130 hp IIRC). It would never idle correctly unless I was running off my trolling tank which was Amsoil syn oil at 100:1 ratio. Regular 50:1 in the main tank (oil injection system disconnected). With the 100:1 the engine just purred all day long, once I changed back to the main tank it idled horrible again.
 
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