Bottom cylinder dead

[rac10860]

2004 15 HP 2 stroke model 15mshc. Has spark, getting fuel, 135 lbs compression. Reed valves look good, replaced lower oil seals and housing. Fires right up but bottom cylinder is still dead. Don't understand why need help

[TownsendsFJR1300]

You everything you need for it to run..

How did you determine the cylinder is not working?

What is the compression in the other cylinder?


All the seals were replaced below the lower end of the crank?

http://www.boats.net/parts/search/Ya...TON/parts.html

[99yam40]

check fuel pump,
if it is dumping fuel into the pulse port of bottom cylinder it will be too rich to fire and burn the fuel

[TownsendsFJR1300]

check fuel pump,
if it is dumping fuel into the pulse port of bottom cylinder it will be too rich to fire and burn the fuel

Makes sense but the fuel pump is attached to the outside of the single carb:

2004 15MSHC Yamaha Outboard CARBURETOR Diagram and Parts

Would that leaking (if a leaking diaphragm) leak over into the lower cylinder?

The pump attaches ONLY to the carb. I don't see any separate lines to the lower cylinder.. ?

[99yam40]

I would think it would be an internal passage if no hoses involved,
has to get a pulse some how

[panasonic]

Swap ignition coils around and see if the problem moves to the other cylinder.

[99yam40]

said it has spark, but who knows

[panasonic]

said it has spark, but who knows

Says he has fuel as well...but no go. One of them is faulty...

[99yam40]

too much fuel is what I told him about

all you can do is guess with the info given

[panasonic]

2004 15 HP 2 stroke model 15mshc. Has spark, getting fuel, 135 lbs compression. Reed valves look good, replaced lower oil seals and housing. Fires right up but bottom cylinder is still dead. Don't understand why need help

How are you checking for spark? Are you using a spark tester?

[ausnoelm]

I think this might be one of those confusing terminology things, he said the cylinder is "dead" doesn't really say not firing, or no fuel or anything else, just dead.

[rac10860]

All lower crank seals have been replaced. Both cylinders have 135 lbs compression. Swapped coils, both cylinders getting spark and fuel.

[panasonic]

All lower crank seals have been replaced. Both cylinders have 135 lbs compression. Swapped coils, both cylinders getting spark and fuel.

How are you checking for spark? Are you using a spark gap tester? Or are you just putting plug in cap and grounding it on the block?

A plug may fire when outside the cylinder but not fire when under pressure installed.

You may not be getting proper voltage from CDI to that cylinder coil...

Please provide detailed information on what you have done. eg "tested for spark with spark gap tester"

If not we can only guess what maybe wrong...

[rac10860]

I checked spark with spark tester both cylinders firing the same, swapped plugs, didn't change anything, bottom cylinder still coasting I'm stumped

[99yam40]

did you check the fuel pump like I said?