2005 Johnson 115 with low compression: noob seeking wisdom

[Harkonnen]

Here is that 2005 2-stroke 115hp Johnson (PLSOR) that I am goofing around with. Compression seems consistently low (90 psi +/- in all 4 cylinders), but starts/idles/runs OK. Any thoughts on how to proceed? Leave it be and deal with it when real trouble starts? Tear down and rebuild now? Something in between? Any wisdom that y'all may be willing to share would be greatly appreciated.

 

[racerone]

Step #1 is a test with another gauge.------Those have a wee hole in the cylinder wall by design.----I do not believe there is anything wrong with your motor.------Write down your compression values.----Don't take this motor apart.

 

[Harkonnen]

Step #1 is a test with another gauge.------Those have a wee hole in the cylinder wall by design.----I do not believe there is anything wrong with your motor.------Write down your compression values.----Don't take this motor apart.

Thanks, that's what I was thinking. If the compression were all over the place, I would have been a lot more worried.

The only reason I started messing with it is because of snot in exhaust (and lousy fuel economy), but I think I narrowed it down to reeds.

 

[racerone]

Well---Why would you suspect reed valve issues ???----I do not believe it is the reed valves at all.---Just put the tool box away and run this motor.

 

[Harkonnen]

Well---Why would you suspect reed valve issues ???----I do not believe it is the reed valves at all.---Just put the tool box away and run this motor.

On the muffs, oily scum floats on top of cooling water, and a few minutes later a good size loogie comes out (couple of tablespoons, maybe more, stinks like gas); lots more than one would expect even from a two-stroke. Bad fuel economy even for an engine this size. Bad smell of gas, with no external gas leaks. Something is not quite right, and I think I ruled out most everything else.

 

[Crosbyman]

normal 2 stroke oil-fuel unburnt floating the barrel ... that is why lots of admins want 2 strokes of their lakes !!

 

[racerone]

Reed valves rarely cause problems.----And reed valves have nothing to do with the perceived low compression in the cylinders.

 

[dingbat]

On the muffs, oily scum floats on top of cooling water, and a few minutes later a good size loogie comes out (couple of tablespoons, maybe more, stinks like gas); lots more than one would expect even from a two-stroke. Bad fuel economy even for an engine this size. Bad smell of gas, with no external gas leaks.

Sounds like your typical 2 stroke.

 

[Harkonnen]

Reed valves rarely cause problems.----And reed valves have nothing to do with the perceived low compression in the cylinders.

True, but I am hearing they could cause trouble with raw gas/oil in exhaust, which was my problem in the first place.

Not that I know much about two-strokes; haven't messed with them since high school.

 

[Harkonnen]

Sounds like your typical 2 stroke.

Way too much even for a two-stroke, IMO. Any thoughts on what should I check to see if it is normal/not normal? Thanks!

 

[racerone]

No they do not cause raw oil / gas in the exhaust !!-----You need to do some testing on your motor.----Review your understanding of what reed valves do and where they are in your motor !-----Sorry if I seem blunt ,--but what do you understand is the purpose of the reed valves and where are they on your motor ?

 

[Harkonnen]

No they do not cause raw oil / gas in the exhaust !!-----You need to do some testing on your motor.----Review your understanding of what reed valves do and where they are in your motor !-----Sorry if I seem blunt ,--but what do you understand is the purpose of the reed valves and where are they on your motor ?

I probably don't - still learning. That's why I'm here. Not that I want to mess with them if I don't have to.

What else is possible? Carb flooding? Fuel pump diaphragm leaking? Thanks!

 

[racerone]

Carburetor float valve is one possibility.----Remove cover in front of carburetors .----Squeeze the manual fuel pump HARD and post what you see.

 

[flyingscott]

On the muffs, oily scum floats on top of cooling water, and a few minutes later a good size loogie comes out (couple of tablespoons, maybe more, stinks like gas); lots more than one would expect even from a two-stroke. Bad fuel economy even for an engine this size. Bad smell of gas, with no external gas leaks. Something is not quite right, and I think I ruled out most everything else.

When was the last time the carbs were serviced? Is the primer in good working condition.

 

[Harkonnen]

When was the last time the carbs were serviced? Is the primer in good working condition.

Last December. Replaced warped bowls and maintenance items. Primer bulb replaced with OEM around the same time.

 

[Harkonnen]

Carburetor float valve is one possibility.----Remove cover in front of carburetors .----Squeeze the manual fuel pump HARD and post what you see.

Yep. Nothing obvious, except that the bulb doesn't go quite as firm as I thought it should, but if I tilt the engine, gas comes out of bottom port carb throat. Looks like a float valve to me. Let's see where I screwed up on rebuild...

 

[racerone]

Are you aware of the basics of a 2 stroke engine ?-----When piston is at bottom of the stroke the intake and exhaust ports are WIDE OPEN.-----Some of the fresh fuel / air / oil goes right through the motor into the exhaust housing.

 

[Harkonnen]

Are you aware of the basics of a 2 stroke engine ?-----When piston is at bottom of the stroke the intake and exhaust ports are WIDE OPEN.-----Some of the fresh fuel / air / oil goes right through the motor into the exhaust housing.

That much I know, but back in my days they didn't have reeds. My previous 2 stroke outboard did not make this kind of mess, either.

 

[racerone]

Outboards have used reeds since 1950 or so.-----What motor did you have that did not use reed valves ?----I am curious here.

 

[Harkonnen]

Outboards have used reeds since 1950 or so.-----What motor did you have that did not use reed valves ?----I am curious here.

MMVZ 3.115 Minsk. But that was an early 80s motorcycle I was playing with in high school. Previous 2 stroke outboard was a 15 hp Mercury (on a different boat), not a drop of oil.

Looks like I found my problem, though, you were right about the carb. Scum is down to believable level, a lot less smoke and stink. Appreciate all the advice!