40hp Dead Top Cylinder

[mebehoof]

Hi All,
I've got a 40hp Johnson with a dead top cylinder.
J40ELCDE
Serial#C7203810 Canada
So I think it's a 1986.
Compression: Top 110psi Bottom 105psi Cold
Had to replace the Primer Solenoid as it leaked.
New Plugs
Lots of spark, tested with spark tester. When it's running I pull the bottom wire it stalls, then I pull the top wire it keeps running.
Checked float bowl on top carb for fuel, pulled the drain screw and fuel came out.
When it's running I choked the top carb by hand no rpm change, when I choke the bottom carb by hand it stalls quickly.
While running I brought up the rpm's above idle speed and sprayed some 2cyl raw gas into top carb with no change in rpm or any indication that it saw the fuel.
So, what I've got is good compression, good spark, fuel available but a dead top cylinder???
This is driving me a bit crazy. Has anyone else experienced this situation? Is there something I'm failing to look for? I look forward to any help and thank you for taking the time to read my questions.
Mebehoof

 

[Faztbullet]

Is it spitting back thru top carb?

 

[saltchuckmatt]

"Tested with a spark tester"

Spark jump tester?

Could be fuel related but not sure you can rule out sparky yet. Is the plug wet or dry?

 

[mebehoof]

"Tested with a spark tester"

Spark jump tester?

Could be fuel related but not sure you can rule out sparky yet. Is the plug wet or dry?

Yes, spark jump tester and grounding the plugs and cranking the engine to watch spark jump the electrode.

The plugs are new so for the little bit that they ran they're actually dry. The one's that were in it were fuel fouled from the broken primer solenoid I think? Replaced primer solenoid on first startup due to leakage.

And like I was posting top cylinder is doing nothing. Pull the wire when running and no rpm change, pull the bottom wire and immediate stall. Can stall it by hand choking the bottom carb also but not the top carb, with the top carb no change in rpm.

Thanks for the reply, much appreciated.

 

[mebehoof]

Is it spitting back thru top carb?

No, no backfire or spitting back on top carb.
Although it has 110psi compression there's nothing happening on the top cylinder. It has spark, compression and fuel so I don't know where to look from here?

Thanks for the reply.

 

[jimmbo]

When you put your hand over the top Carb, did you feel any Suction? A bad Intake Manifold to Block Gasket can prevent Crankcase Inhalation/Compression, as can a bad/worn Upper Crankshaft Seal.
Look on the outside of the Block. Is there any signs of Oil running down the Outside?

 

[saltchuckmatt]

Dry plugs and no power can certainly point to no fuel or internal compression issues but how far did the spark jump on your measured spark test?

 

[racerone]

Check the reed valves.----I believe compression on that should be around 140 PSI.-----Here the cylinder head would be off in minutes to have a look.---Head gasket is cheap.----Your location?

 

[mebehoof]

Check the reed valves.----I believe compression on that should be around 140 PSI.-----Here the cylinder head would be off in minutes to have a look.---Head gasket is cheap.----Your location?

Hi, Thanks for the reply... I'm in St Clair County, Mi near Port Huron, Mi.
You said, "Here the cylinder head would be off in minutes to have a look." What do you mean, pull it apart to diagnose?
mebehoof

 

[mebehoof]

Dry plugs and no power can certainly point to no fuel or internal compression issues but how far did the spark jump on your measured spark test?

The spark jumped a long way like 3/4" to 1" when I stretched it. Spark is pure blue (normal in appearance).
Compression, fuel available, plenty of spark but dead top cylinder.
mebehoof

 

[mebehoof]

When you put your hand over the top Carb, did you feel any Suction? A bad Intake Manifold to Block Gasket can prevent Crankcase Inhalation/Compression, as can a bad/worn Upper Crankshaft Seal.
Look on the outside of the Block. Is there any signs of Oil running down the Outside?

Very little suction when covering carb.
Outside of outboard does have some streaks of oil running down but I thought it was from when first starting it this year the choke/primer solenoid leaked gas. (I thought it was from the leaked gas mixing with residue in the housing and just mixing with the oil and junk in the housing and running down)
mebehoof

 

[racerone]

Just take the cylinder head off.----Easy to do.----Will teach you a lot.----I am a little more than 2 hrs away ( north ) from you.----Canadian side of the big lake.

 

[mebehoof]

Just take the cylinder head off.----Easy to do.----Will teach you a lot.----I am a little more than 2 hrs away ( north ) from you.----Canadian side of the big lake.

Hello there neighbor, eh.
I'm getting messages in the thread regarding reed valves and other items (I'm sure you saw the posts) so I'm a bit gun-shy. FYI, I am and have been a mechanic literally all my life. Cars, trucks, and had a marine repair business in the 80's and 90's which only worked on large craft, no outboards ever (except my own). So, I've seen a lot of pistons in my day and I'm not sure what exactly pulling the head would show me????? I suppose whether the cylinder is running normally or wet or carboned up and I know the view but I'm chasing a dead top cylinder. When running little to no suction on top carb, no rpm increase with raw fuel sprayed in top carb, lots of good spark (hoping it's getting there at the right time) and when running pull top plug wire and no rpm change, pull bottom wire and stalls immediately.
mebehoof

 

[racerone]

Good luck with your motor.

 

[mebehoof]

Good luck with your motor.

Hi again racerone, was hoping to hear a bit more of thoughts on what to do to diagnose this engine? If you have any thoughts that might help I'd surely appreciate it. TIA mebehoof

 

[racerone]

Sorry----There is very good input posted.-----You seem reluctant to act on it.

 

[tphoyt]

A valuable lesson I have learned on here over the years is Racers knowledge is worth its weight in gold. If you want his help you need to answer the questions with findings and or results and not more questions. I could go into a rabbit hole trying to explain what I mean but in a nut shell if you do the leg work so you can answer the questions you will get the results your looking for.
Best

 

[saltchuckmatt]

You could pull the head, get valuable information, resurface it and install it in less than 3 hours.

With two strokes sometimes it's more than compression, spark and fuel.

Your either over looking something or it's something stupid like coils receiving the wrong info....

 

[mebehoof]

Sorry----There is very good input posted.-----You seem reluctant to act on it.

Not at all reluctant, it seems I'm plagued with 4 stroke knowledge and thinking in 4 stroke terms. I do appreciate the input and intend to act on it. I don't want this engine to be a brick. Thanks

 

[jimmbo]

Very little suction when covering carb.
Outside of outboard does have some streaks of oil running down but I thought it was from when first starting it this year the choke/primer solenoid leaked gas. (I thought it was from the leaked gas mixing with residue in the housing and just mixing with the oil and junk in the housing and running down)
mebehoof

"Very little Suction"... Was Fuel getting sprayed back on your Hand when you covered the Carb?
Are the Oil Streaks on the Block, along the Crankcase Seam, or coming down from under the Flywheel?