140 johnson outboard misfire at idle

[boating maniac]

What should I start with first when diagnosing a constant misfire at idle from 1100 to 1400rpm? Above that it runs fine.

Replaced spark plugs and it still does it.

 

[wired247]

Re: 140 johnson outboard misfire at idle

partially clogged or gummed up idle jet. If it leans out or runs too rich on the idle circuit you'll get a missfire. If you get a can of carb cleaner with the straw and stick it into the idle air jet you can flush out that whole circuit.

 

[boating maniac]

Re: 140 johnson outboard misfire at idle

Will their be an H or an L next to the mixture screw marking whether or not it's the low speed or high speed jet? This is a 1991 model crossflow. It has two carbs.

 

[boating maniac]

Re: 140 johnson outboard misfire at idle

Alright well I took off the plastic cover to get to the carb throats and it looked like the low speed jet on the bottom starboard cylinder was gunked up. All the other jets you could see a nice open hole except for that one so hopefully thats the problem. Oh and I went ahead and sprayed them all while I was at it.

 

[emdsapmgr]

Re: 140 johnson outboard misfire at idle

Can you clarify the model year? The last year for a 140 crossflow was the 1984 model year. Perhaps you have a 115 hp crossflow engine. The 1991 140 was a big bore looper engine.

 

[archcycle]

Re: 140 johnson outboard misfire at idle

Sounds like you probably found the cause, but if it continues, do you have a timing light or a spark tester? Intermittent spark will cause that at low speeds while it becomes harder to notice the ill effects once the motor gets some inertia going even while still missing sparks. A spark tester from an auto store is a good way to check for a no spark condition but you need a timing light to check for intermittent spark on each cylinder while it's running.

 

[boating maniac]

Re: 140 johnson outboard misfire at idle

Can you clarify the model year? The last year for a 140 crossflow was the 1984 model year. Perhaps you have a 115 hp crossflow engine. The 1991 140 was a big bore looper engine.

It's a 1991 VJ140TLEID It's 140hp.

 

[archcycle]

Re: 140 johnson outboard misfire at idle

Well good news you have a looper not a cross flow

Better idle.

 

[boating maniac]

Re: 140 johnson outboard misfire at idle

Took the boat out today. It ran great. What does looper and crossflow stand for? I think periodically i'm going to remove that plastic cover and spray carb cleaner down the carb throats just as a precaution.