86 johnson 40hp backfires, wont start

[tim0629]

Hi all,

1986 johnson 40hp 2 stroke outboard not starting, only occasional backfire.

Previously had an issue of low power under load which sent me on a warpath cleaning and replacing parts.
- New plugs. I've test rigged these to watch them fire nicely.
- carbs soaked in chem dip and boiled in water. Picked the orifices, compressed air through passages and the whole deal.
- rebuilt carbs with new needle valve, orifice plugs and gaskets. I am 93% confident the carbs are super clean.
- New fuel pump. Confirmed working by letting it pump unhooked from carbs
- new fuel lines from carbs all the way back to tank. These were cracked before - much to do with the original problem i was trying to fix.
- New thermostat
- Removed and cleaned reeds. I used brp gasket sealant when reinstalling the reed valve housing.

I've also...
- confirmed spark, gaps 7/16" consistent and strong
- confirmed timing with timing light. Idle timing at 2 degrees ATDC. Start position timing 2 degrees BTDC. WOT is around 14 BTDC
- confirmed that TDC of the primary piston matches TDC markings on the flywheel (rough confirmation with a screwdriver used to measure piston position through the plug port).
- fuel is fresh, mixed 50:1 + a few ounces of seafoam in a 5 gallon tank
- compression good on both cylinders around 120psi
- no sign of water in the fuel
- carb bowls fill nicely.
- can feel nice suction through the carb throats

I did not have a startup problem before replacing and cleaning parts... but now the motor does not pop at all, just the occasional backfire. I am troubleshooting on muffs in the driveway.

I let it sit overnight thinking that maybe it was flooded. No luck this morning. Plugs appear to get wet but not excessive. Just the amount of wet one might expect when the cylinders are not firing.

Has anyone ever had problems created when reed valves or carbs were cleaned? The one thing that is very curious to me is the gooey nature of the gasket sealant provided by BRP. It doesnt solidify and I fear that it may have fouled the reed valves potentially... but uncertain if these symptoms jive with fouled reed valves. Before I tear it apart again I wanted to collect some ideas.

Completely stumped here. Any ideas would be appreciated greatly.

Thank you!
Tim

 

[racerone]

Check flywheel key.-----And no you can not find a sheared key with a timing light.

 

[tim0629]

Check flywheel key.-----And no you can not find a sheared key with a timing light.

Thanks racerone,
I found TDC on the primary cylinder by sticking a screwdriver into the cylinder and rotating the flywheel until the piston "peaks." The TDC marking on the flywheel matches the arrow at that same location - doesn't that imply that the flywheel hasn't slipped? I'm open to pulling the flywheel but I don't have a puller so I was just trying to reason through it before I went there and got a puller and strap wrench.

Thanks!

 

[racerone]

I agree that flywheel key is in good shape on your motor.---Sounds like a lean sneeze to me then.------Possibly throttle plates opening too soon.-----Are both throttle plates CLOSED at idle?

 

[tootallofwa]

Ok so you have poor power under load... I get the check for spark, and fuel pressure. If it runs, then it's probably not the carburetor but rather Synchronization or adjustment that is your problem. Backfiring sounds like "Lean Sneeze" to me. Loosen the high-speed needle 1/4-1/2 turn Counterclockwise.
What provoked you to clean the reed valves and use gasket sealant?? You should have bought the repair manual, I'm fairly certain the gaskets should have been dry.

 

[tootallofwa]

I should also say that it is not safe to run your motor at Wide Open Throttle with "Muffs".
and Diesel fuel makes a GREAT carburetor cleaner, No need to "boil" out the residue.
Oh... check your kill switch wiring.

 

[Edchris177]

Did you by chance hook the plug wires to the wrong cylinder?

 

[tim0629]

I agree that flywheel key is in good shape on your motor.---Sounds like a lean sneeze to me then.------Possibly throttle plates opening too soon.-----Are both throttle plates CLOSED at idle?

Both throttle plates do fully close, photo attached for reference but I also manually grabbed the throttle position arm to make sure the spring is fully returning the throttle plates. No apparent issue here.

Regarding your comment about lean - i was thinking lean as well but the one thing that is can't wrap my head around is that the tube i am pointing at in the other photo attached tends to burp out fuel when I crank the motor. I'll take the plugs off and hand crack the flywheel and watch an ounce or two burp out of that tube. I think it is a crankcase flood vent tube... which keep taking my mind to flooding. Further - priming the motor does not help at all. It may just increase the frequency of backfiring.

 

[tim0629]

Ok so you have poor power under load... I get the check for spark, and fuel pressure. If it runs, then it's probably not the carburetor but rather Synchronization or adjustment that is your problem. Backfiring sounds like "Lean Sneeze" to me. Loosen the high-speed needle 1/4-1/2 turn Counterclockwise.
What provoked you to clean the reed valves and use gasket sealant?? You should have bought the repair manual, I'm fairly certain the gaskets should have been dry.

The original problem was loss of power under load yes. I BELIEVE the problem was deteriorated fuel lines going from the input to fuel pump and fuel pump to carbs. But I didn't realize this until after I went on a crusade cleaning carbs, reed valves spark plugs etc.

You are the second mention of "lean sneeze" now. I made one comment/question on it above, but I am intrigued. Unfortunately, this model (j40telcde) does not have any adjustability of the carb jets. See photo from manual below for reference. So there isn't much i can do there.

I did bend the float just a tad to get it level to the housing when I rebuilt the carb - maybe that was not a good idea idk.

RE: your comments about the reed valve. I actually do own a repair manual and it clearly states to install the gasket dry as you mentioned. My wife will back me up here when I say that I tend to avoid reading stuff, and I pay for it later. I removed the reed valve cover, re-cleaned the reed valves and cover and cleaned the gasket of all sealant at this time. There was one small notch (maybe 0.5mm x 1mm long) in the leaf seat area of the leaf valve block that I did not photograph. Wasn't convinced that this would be the problem but it's note worthy.

The reason I went after the reed valves relates to my comments about the original problem I had about loss of power under load. I was going through everything I could think of, and the reed valve made it on my list of things to take out and check.

 

[tim0629]

I should also say that it is not safe to run your motor at Wide Open Throttle with "Muffs".
and Diesel fuel makes a GREAT carburetor cleaner, No need to "boil" out the residue.
Oh... check your kill switch wiring.

I will check the kill switch wiring, but doesn't the presence of spark negate this theory? I still see spark across a gap tester and my timing light is firing during testing. My understanding is that kill switch kills spark.

 

[tim0629]

Did you by chance hook the plug wires to the wrong cylinder?

Hi EdChris
Yes I did check for this as well. I also confirmed that my timing light on the primary cylinder that it is firing around 2 degrees ATDC at idle and 2 degrees BTDC at the start position, and that the flywheel TDC markings does correlate to the actual TDC position of the primary cylinder. Photo attached for plug wiring on the cylinders.

 

[racerone]

You set MAXIMUM timing advance.-----Idle timing is when THROTTLE PLATES OPEN.-----Actual timing at smooth / slow idle does NOT matter.-----That tube scavenges fuel from the airbox, should a carburetor leak.----Compression should be 140 PSI + , but that might be your gauge reading low.

 

[tootallofwa]

I hope you got your engine running again.
Oh! did you check to see if your prop has spun or loose on its rubber hub? That will cause a loss of power too.

 

[FishAtFive]

I have a very similar problem, did you ever figure out what the issue was?

 

[tim0629]

I have a very similar problem, did you ever figure out what the issue was?

Im embarrassed to say but when I put the motor all back together I must have swapped the leads going in to the ignition coils (from the power pack). So there cylinders were sparking 180 degrees from when they should have been and just backfiring like crazy.

Hours of dinking. $200 in parts and Products. Lots of frustration.

Hope this helps!

 

[Edchris177]

I should have mentioned in my post…not only to check plug wires being wrong, but ignition leads. Easy to do when all apart. Take photos, before anything removed. Pay attention to small things like color coding on wires. Saves a lot of $$ and aggravation.

 

[tim0629]

I should have mentioned in my post…not only to check plug wires being wrong, but ignition leads. Easy to do when all apart. Take photos, before anything removed. Pay attention to small things like color coding on wires. Saves a lot of $$ and aggravation.

Lesson learned. I do/did tape and mark all the bolts and wires and wires and take photos and video as I pull things apart for this reason exactly. Of course these two leads are the same length and almost identical in color so it just slipped by. Murphy strikes again.

What i found to be very misleading (and still am confused about) is that when I put a timing light on the primary cylinder lead (which went to the correct coil but that coil had the incorrect lead from the power pack), it was showing me that the cylinder was firing around TDC. I thought this was a clear indication that the cylinder was firing at the correct time.

I do not know how to explain this. maybe when you just crank an engine and its not firing up - the apparant timing is irrelevant? Idk. Very confused on that one

 

[FishAtFive]

Im embarrassed to say but when I put the motor all back together I must have swapped the leads going in to the ignition coils (from the power pack). So there cylinders were sparking 180 degrees from when they should have been and just backfiring like crazy.

Hours of dinking. $200 in parts and Products. Lots of frustration.

Hope this helps!

Wow, that was my same exact problem. Whoever installed the power pack years ago switched those wires. I guess I should be thankful, if not for that I probably would not have this motor! I never would have figured it out if not for a member here racerone knew exactly the problem.