40hp Dead Top Cylinder

[racerone]

There are 2 separate crankcases.-----The top carburetor is for the top cylinder only.

 

[mebehoof]

There are 2 separate crankcases.-----The top carburetor is for the top cylinder only.

racerone,

OK, since each cylinder is independent regarding fuel/air and compression that narrows the problem down a bit.

I just got rained out pulling the reeds but with the carbs off and a flashlight they look really clean and seated from the carb side. Pristine clean. I'm wondering that since it has compression though not 140psi if this could be some sort of ignition system problem? The coils are working, wires are good, plugs new and fire normally. Also as I had mentioned when I spritzed raw fuel/mix into top carb, no rpm change and suction is the same roughly top and bottom but when full hand choking top no rpm change, chocking bottom immediate stall.

mebehoof

 

[mebehoof]

bad reeds or not no /low suction means air is entering from a source other than the carb...

Crosbyman,
Thank you for the video, very helpful. I should change my handle from mebehoof to 2stroke/student

mebehoof

 

[racerone]

Do you not want to take the cylinder head off ??----Simple / easy job.

 

[cyclops222]

1 last test to do will define where to go next. You have the lower carb in decent running . Swap the top and bottom carburetors. If the trouble follows the carburetor. done. If NO CHANGE ? Do racerone procedure. The problem is then a internal one.

 

[jimmbo]

Spraying fuel into carb makes no diff, and disconnecting Sparkplug wire makes no diff, Perhaps the Plug is somehow defective, try swapping them

 

[Lpgc]

Do you not want to take the cylinder head off ??----Simple / easy job.

I understand why lack of compression could cause the issues (but he has compression) and I understand whybad reed valves wouldn't affect 2 stroke compression, but since we know there is compression I don't know what info could be gained from pulling the head?

Heh, I was thinking reed valve before the OP said the top carb seems to suck as much air as the bottom carb.

I don't want to take this thread off topic but the (different engine) Merc 70 I rebuilt had 3 cylindersbut only 2 carbs... the cylinders must all have been drawing from more than one carb on that engine (crank not partitioned)?

 

[racerone]

Lpgc----Nonsense , the 3 cylinder MERCURY you speak of has 3 separate crankcases.---Like al inline 2 strokes each cylinder needs seperate crankcase for compression below the piston !

 

[Crosbyman]

Crosbyman,
Thank you for the video, very helpful. I should change my handle from mebehoof to 2stroke/student

mebehoof

utube is your friend. ... but 50+ years of boating helps.

" Time is the best teacher it's only drawback is that it kills it's students "

 

[jimmbo]

I don't want to take this thread off topic but the (different engine) Merc 70 I rebuilt had 3 cylindersbut only 2 carbs... the cylinders must all have been drawing from more than one carb on that engine (crank not partitioned)?

The center Cylinder drew from both Carbs. Created some very odd flow through the carbs, which in 2, 4, and 6 cylinder inlines, had induction draw from 2 cylinders 180 degrees apart. with more or less Equal Pressure Drop. With 2 carbs for 3 cylinders, the flow wasn't as even

 

[mebehoof]

1 last test to do will define where to go next. You have the lower carb in decent running . Swap the top and bottom carburetors. If the trouble follows the carburetor. done. If NO CHANGE ? Do racerone procedure. The problem is then a internal one.

cyclops222,
Moved carbs and moved the problem to the other cylinder. took carb off, soaked in dip and cleaned it up and blew it out... put it back in its original spot (bottom) still same problem. Once again just to be sure moved to top cylinder and it moved the problem... Question: could this be a defective carb??? At a loss which way to go with it now??? Replace Carb???

Thanks for reading, mebehoof

 

[cyclops222]

After watching the videos. The reduced compression readings look like possible worn out Reed Valves with some possible piston ring wear.
New reed valves are cheap and simple. Maybe all that is needed to get closer to 140 PSI compression readings.
Bad carb needs to be rebuilt ? Check float settings and needle passages. Both air and fuel paths.
Check the float and needle tip for damage.
If you are not VERY confident with doing other carburetors' in the past ? DO NOT do this carb at all have a marina mechanic do the job.
Same with changing just the reeds. Some do require ability to get a perfect sealing of the edges. Good luck.

 

[cyclops222]

look up www.crowleymarine.com

 

[racerone]

The reed valves have nothing to do with compression in the cylinders !----You can throw the reed valves under the work bench and get good compression readings !

 

[jimmbo]

cyclops222,
Moved carbs and moved the problem to the other cylinder. took carb off, soaked in dip and cleaned it up and blew it out... put it back in its original spot (bottom) still same problem. Once again just to be sure moved to top cylinder and it moved the problem... Question: could this be a defective carb??? At a loss which way to go with it now??? Replace Carb???

Thanks for reading, mebehoof

Just soaking carbs isn't going to get all the Gunk out of the Passages. That is why the OEM Carb Kits come with little Disks and Lead Balls. The matching ones on the Carb, have to be removed to gain Access to where Gum/Varnish/Dirt hide and cause issues.

 

[tphoyt]

Endless the carb is physically damaged there is not much that can go wrong that a through cleaning and rebuild can’t fix. Hopefully you didn’t run it like that for very long and damage anything as no fuel = no oil. But you won’t know that until you pull the head and take a peak.

 

[saltchuckmatt]

After watching the videos. The reduced compression readings look like possible worn out Reed Valves with some possible piston ring wear.
New reed valves are cheap and simple. Maybe all that is needed to get closer to 140 PSI compression readings.
Bad carb needs to be rebuilt ? Check float settings and needle passages. Both air and fuel paths.
Check the float and needle tip for damage.
If you are not VERY confident with doing other carburetors' in the past ? DO NOT do this carb at all have a marina mechanic do the job.
Same with changing just the reeds. Some do require ability to get a perfect sealing of the edges. Good luck.

What does this even mean? He changed the carb and the problem followed.

 

[saltchuckmatt]

Clean or rebuild it properly or buy one from anywhere really. Cheap.

 

[mebehoof]

Clean or rebuild it properly or buy one from anywhere really. Cheap.

Anyone have any idea where to find a replacement top carb for this 40hp Johnson Model#J40 ELCDE carb #395790 MX K 04 L K

Carb #395790
MX
04 L K

Any help will be greatly appreciated. Found (I hope) complete rebuild kit from the place cyclops222 mentioned @ www.crowleymarine.com

Gonna watch this thread for carbs pointers then if nothing call Crowley Marine.

Thanks everyone, hope I don't have to tear it down but if so, will do.
mebehoof

 

[jimmbo]

Thanks everyone, hope I don't have to tear it down but if so, will do.
mebehoof

You would likely be better off taking this one apart for Cleaning, and Adjustment, than buying another potential Set of Problems