Johnson 40 hp not firing on both cylinders

[tloc1000]

I've got a 40hp two cylinder. Bottom cylinder is not firing. I took the wires off while it was running. That's how I determined which cylinder wasn't running. When I took the top one off, it shocked the crap out of me and the motor died. I put it back on, fired it up, and took the bottom one off. It shocked the crap out of me but kept running. Lol. I swapped plugs and wires; wires & plugs are good. Top cylinder fires no matter which plug or wire is used. Tried to swap coils, top coil fires with top cylinder but if I put the top coil on the bottom cylinder it doesn't fire. If I put the bottom coil on the top cylinder it doesn't fire. You think it's the coil or something else?

 

[Bosunsmate]

So after all your shocking do you know if you get any spark on the bottom cylinder? It may be a fuel or compression issue if you get spark there

 

[tloc1000]

It arcs to the block but don't know how strong a spark it is. I figured it had spark since it was a shocking experience.

 

[gm280]

tloc1000, first things first. :welcome: aboard to iboats. Glad to have you as a new member...

You stated you have a Johnson 40 HP OB engine, but you didn't specify the year, model or serial numbers, and such things. Those things are important when trouble shooting an engine.

WHen trying to verify if a cylinder is firing, you remove the spark plug wire (with an insulated glove or something like that). It the engine changes RPMs that cylinder is firing and good. If you remove the spark plug wire and it doesn't change the engine RPMs it is a dead cylinder. Getting shocked pulling off spark plug wires doesn't necessarily mean the spark is good either.

Have you done a compression test. A cylinder with poor compression can have the best spark in the world and not fire properly. So start with a compression test and let's go from there. Post those compression numbers and let's see what is going on. Could be you have more then one problem, JMHO

 

[tloc1000]

Ok so while running, it won't idle I have to have the throttle about 1\3 to keep it running, if I spray cab cleaner I to the lower carb, it revs up. If I spray carb cleaner in the top carb it bogs down.

 

[tloc1000]

Thank you GM280. I'm working on getting a compression tester. It is a [h=1]1990 Johnson TJ40ELESR[/h]

 

[Bosunsmate]

Sounds like you need to clean your lower carb, it either has a stuck closed float or one of the small passages a clogged up. You need to fix that before you run the motor again as if its short on fuel you can end up damaging the cylinder but dont worry too much about that as that most often happens on motors with like 6 cylinders where the engine keeps running on 5 and the other one burns up as you just dont get so much signs something is wrong

 

[Bosunsmate]

It could also be your bottom crankshaft seal but much more likely the carb. Lots of threads on that. Just use some soft copper wire to clean out those tiny passages and something like wd40 if you cant afford carb cleaner, post photos if you a unsure and make sure you put back as you find it. You may need the cheap gasket between carb and engine but see how easily yours comes off

 

[tloc1000]

Thanks Bosunsmate!

So it seems my original diagnosis of a not firing cylinder was wrong? I guess it was just so weak that it couldn't keep the motor running.

 

[Bosunsmate]

Thanks Bosunsmate!

So it seems my original diagnosis of a not firing cylinder was wrong? I guess it was just so weak that it couldn't keep the motor running.

Not sure yet, need to wait til its solved.
But adding fuel to the lower carb and getting it picking up indicates that it had no fuel to run and getting a shock although not the best indicator suggets you do have spark on the bottom cylinder, so its firing but theres no fuel in it so it wont work.
So its firing spark but it has no power due to no fuel, so it isnt firing i guess you can kind of say.
You need spark, fuel and compression for a cylinder to work

 

[89Aluma]

Really you could probably solve the problem by just doing a full tune up. When you start having issues it's best to just do a tune up and see where that takes you. Do the coils wires plugs clean the carbs do the impeller since their cheap anyway if that doesn't solve the issue it's probably a bad seal or gasket. When is the last time those items have been replaced? Or cleaned?

 

[tloc1000]

Really you could probably solve the problem by just doing a full tune up. When you start having issues it's best to just do a tune up and see where that takes you. Do the coils wires plugs clean the carbs do the impeller since their cheap anyway if that doesn't solve the issue it's probably a bad seal or gasket. When is the last time those items have been replaced? Or cleaned?

Thanks 89. I just got the boat so I'm not sure how long it had been sitting. The PO said that he had just put in a new impeller and had the carbs rebuilt. I know I can't take his word for it but the motor does look like it has recently been worked on.

I didn't get a chance to work on her last night but plan on pulling the carb tonight and doing some cleaning. I'll also swing by Northern Tool and get a compression tester.

 

[tloc1000]

I borrowed a compression tool and got 120 from both cylinders. I took both carbs off and even though it looks like they were just serviced (had new gaskets) I took them apart and cleaned them with carb cleaner and a strand of copper wire. The idle screws were almost 8 turns out so I put them back to 1.5 turns. I also replaced the fuel filter. My buddy that I borrowed the compression tool from said that I may want to check all the fuel lines. He had a boat where the fuel lines were breaking down and getting trash in the carbs. He said he cleaned the carbs about 4 times before he figured that out. I took the lines off and they were soft and we're not breaking down. I figured a new fuel filter would be good anyway. It's running and idling great in a bucket. I'll be going to the lake in the morning. I'll keep you updated.

Thanks all for all the help! It's greatly appreciated.

 

[tloc1000]

Took her out this morning and she runs like a champ!!!!! She idled great, went into gear, and didn't bog/ hiccup/sputter when going from full stop to full throttle. She pulled to the right pretty bad so I adjusted the tab by the prop and got her going straight. We ran about 1.5 hours with no problems!

I've still got to double check the gear oil and get everything rewired. Previous owner ripped out all the wiring.

Thanks for all the help!

 

[Bosunsmate]

No worries, im glad it was a cheap fix, they pretty much always a if you do it yourself