68 9.5 rude just wont rev out.

[RaisedByWolves]

Did you miss the part where I added oil to the cylinder and the compression went into the normal range?

 

[MrGiggles]

Did you miss the part where I added oil to the cylinder and the compression went into the normal range?

It would increase on a perfectly healthy engine too, to what extent depends on many variables.

I would at least pull the head before making any hard determinations, if isn't scored up and the rings aren't stuck, should be fine.

 

[RaisedByWolves]

Im normally right there with you, but I cant figure why this has no power.

 

[Sinkingfast]

Some motors have the piston thrust towards the exhaust and others are towards the transfer port. They are affected differently when there is a lot of blowby. Don't know about that particular motor...


Had a merc 4hp that was weak like your motor...sat for 20 years. Ran it with 20/1 for a tankfull. Came back 1/2 way. Ran it another tankfull and it now is back to full song.

...and that's the truth... :mrgreen:

 

[Pappy]

A "perfectly healthy" engine will not have a 20# increase in compression with the simple addition of oil to the cylinder.
A long hose on a compression ga. should not affect the reading. The gauge should be calibrated for that volume.
What WILL have an effect on any compression gauge is the substitution of of a different Shrader valve other than an original replacement. Shrader valves are not all the same. Far from it. They all have different spring pressures internally and therefore different pop=off pressures. These differences will produce vastly different readings from the valve the gauge came with.
I went through Hell trying to get an original for my MAC Tools compression gauge (with hose). The Shrader valve blew in it and most common replacements would give me low readings. The other mechanic at the shop just happens to have an identical MAC Tools gauge to mine. I kept learning about different Shrader valves and finally found the right one that would match numbers to a known good gauge.
Keep this in mind when playing with compression gauges.

 

[user 21074]

I worked on a coworkers family hand me down motor, carb kit/impeller and reseal of the lower unit.

Unfortunately after I worked on it, he worked on it........dont ask, hes a bonehead.


Anyway, the motor starts and idles fine, low speed running is great, but thats all that it will do.

It only pushes his 14' boat @ about 3mph.

The motor sounds good, but it just wont rev out and bring the boat up on plane.

Where would you start.

Go to Leeroys Ramblings..best info on these you can get.Compression on these is good at 70/75.Just got one of these running with about 70.Ran 14mph on my jon.Also.The high speed jet should be taken out.Cannot clean it properly the way it sits in the bowl behind the drain screw.

 

[user 21074]

I believe on those OMCs, the orifice for the main jet is in the bowl of the carb, not in the main body like most. There is a rubber donut gasket that seals the two together. If that is missing, it will idle all day but totally fall on it's face when revved. The plugs will be wet and it may flood out. Make sure it's there and in good shape.

Im not seeing an o-ring on this diagram.

Pappy, I took it out and ran it solo and there was no bog, it just revved to a certain point and stayed there.

I added choke with no change. Well, it did die off a lil like it was going over rich but no change for the better.

I pumped the ball with no change.

Checked it was firing on both cylinders.

I did read on THT that there were some bad pump diaphragms from sierra so Im going to change that out and see if there is any change, but I would think that would have shown its self when I pumped the ball?

Stumped.

He is referring to the carb gasket I believe.

 

[user 21074]

Just went out to double check compression and it dont look good.


75 cold that bumped to over 90 with oil in the cylinder.

Good compression is 75.

 

[ClemsonAlum]

One more easy item to check: Look at the kill wire where it is held in place to the housing by a washer type piece. The one on my motor had bad insulation (original wire) and rubbed off from vibration, grounding out the coils partially. I replaced mine and saw some power gain.

-Kurt
1436 PolarKraft & 9.5 Evinrude

 

[RaisedByWolves]

Just went out to double check compression and it dont look good.


75 cold that bumped to over 90 with oil in the cylinder.

Good compression is 75.

How do you account for no change in power regardless of what’s done to it.

If it was fuel it should have responded to adding choke, but it didn’t pick up at all, it only bogged near full choke.

Main jet was removed for carb rebuild.

 

[RaisedByWolves]

One more easy item to check: Look at the kill wire where it is held in place to the housing by a washer type piece. The one on my motor had bad insulation (original wire) and rubbed off from vibration, grounding out the coils partially. I replaced mine and saw some power gain.

-Kurt
1436 PolarKraft & 9.5 Evinrude

Kill switch was replaced the day before I took it out.

 

[MrGiggles]

A "perfectly healthy" engine will not have a 20# increase in compression with the simple addition of oil to the cylinder.
A long hose on a compression ga. should not affect the reading. The gauge should be calibrated for that volume.
What WILL have an effect on any compression gauge is the substitution of of a different Shrader valve other than an original replacement. Shrader valves are not all the same. Far from it. They all have different spring pressures internally and therefore different pop=off pressures. These differences will produce vastly different readings from the valve the gauge came with.
I went through Hell trying to get an original for my MAC Tools compression gauge (with hose). The Shrader valve blew in it and most common replacements would give me low readings. The other mechanic at the shop just happens to have an identical MAC Tools gauge to mine. I kept learning about different Shrader valves and finally found the right one that would match numbers to a known good gauge.
Keep this in mind when playing with compression gauges.

Depends on what oil, how much, and other factors. There are no hard and fast rules and too many variables to strictly say that the engine is junk just from a wet compression test, performed by somebody else.

Hose length will make a difference. A simple calibration in the gauge will not cover all situations, it would read normal on small engines, and high in automotive, or vice versa.

The volume of the hose between the schrader valve and the piston effectively increases the combustion chamber volume, on an engine of larger displacement, it doesn't make much of a difference, but on a small engine, those few extra CCs do. For small engines, you need a hose adapter with the schrader placed right about where the spark plug electrode would be, hose length after the schrader has no affect, will just take more or less pulls to get a peak reading.

 

[user 21074]

Just went out to double check compression and it dont look good.


75 cold that bumped to over 90 with oil in the cylinder.

Good compression is 75.

How do you account for no change in power regardless of what’s done to it.

If it was fuel it should have responded to adding choke, but it didn’t pick up at all, it only bogged near full choke.

Main jet was removed for carb rebuild.

How about a clogged exhaust port?Have heard of heavy build up causing this reducing flow.Then again it may still get to proper rpms,but lose power?Does it have the right prop on it? Have you checked the rpms on it.I use a tiny tach for my 20hp to aid in troubleshooting and set up.

 

[Weldorthemagnificent]

Rings could be sticky too. Have you decarbonized it? Evinrude makes a tune-up spray, so does mercury, Quicksilver, Seafoam etc. My '69 9.5 ran when I got it. I poured a bunch of Seafoam down the carb, in the plug holes and put plugs back in. Layed the motor down and turned it every few hours for a couple days. Plunked it in the barrel and fired it up. It smoked like a forest fire for a bit and all manner of junk came out if it but it did pick up some power and ran better on the top end. On my 12' Harber Craft with a 230 lb dude and a hundred pounds of gear it will get a solid 12 mph GPS.

Sent from my CLT-L04 using Tapatalk

 

[RaisedByWolves]

A "perfectly healthy" engine will not have a 20# increase in compression with the simple addition of oil to the cylinder.
A long hose on a compression ga. should not affect the reading. The gauge should be calibrated for that volume.
What WILL have an effect on any compression gauge is the substitution of of a different Shrader valve other than an original replacement. Shrader valves are not all the same. Far from it. They all have different spring pressures internally and therefore different pop=off pressures. These differences will produce vastly different readings from the valve the gauge came with.
I went through Hell trying to get an original for my MAC Tools compression gauge (with hose). The Shrader valve blew in it and most common replacements would give me low readings. The other mechanic at the shop just happens to have an identical MAC Tools gauge to mine. I kept learning about different Shrader valves and finally found the right one that would match numbers to a known good gauge.
Keep this in mind when playing with compression gauges.

Depends on what oil, how much, and other factors. There are no hard and fast rules and too many variables to strictly say that the engine is junk just from a wet compression test, performed by somebody else.

Hose length will make a difference. A simple calibration in the gauge will not cover all situations, it would read normal on small engines, and high in automotive, or vice versa.

The volume of the hose between the schrader valve and the piston effectively increases the combustion chamber volume, on an engine of larger displacement, it doesn't make much of a difference, but on a small engine, those few extra CCs do. For small engines, you need a hose adapter with the schrader placed right about where the spark plug electrode would be, hose length after the schrader has no affect, will just take more or less pulls to get a peak reading.

How is the hose length going to affect a wet vs dry compression test.

Ive studied automechanisc and have worked on engines all my life and never heard ant talk of what type of oil to use other than simply motor oil.

The oil I used was even lighter, probably about 10wt machine oil.

If you dont have this oil/oiler, get some.


The empty bottle and extendible spout make this a great tool to prime and engine for a quick start and to check and eliminate fuel delivery issues.

Extend the spout, squeeze the bottle then put spout into container of gas and let it suck gas out of tank. You now have a couple ounces of fuel to prime an engine, light a fire, soak your sneaker with. :shock:

 

[RaisedByWolves]

Good compression is 75.

How do you account for no change in power regardless of what’s done to it.

If it was fuel it should have responded to adding choke, but it didn’t pick up at all, it only bogged near full choke.

Main jet was removed for carb rebuild.

How about a clogged exhaust port?Have heard of heavy build up causing this reducing flow.Then again it may still get to proper rpms,but lose power?Does it have the right prop on it? Have you checked the rpms on it.I use a tiny tach for my 20hp to aid in troubleshooting and set up.

Prop is brand new and just try finding something other than the stock size/pitch out there.

 

[MrGiggles]

A "perfectly healthy" engine will not have a 20# increase in compression with the simple addition of oil to the cylinder.
A long hose on a compression ga. should not affect the reading. The gauge should be calibrated for that volume.
What WILL have an effect on any compression gauge is the substitution of of a different Shrader valve other than an original replacement. Shrader valves are not all the same. Far from it. They all have different spring pressures internally and therefore different pop=off pressures. These differences will produce vastly different readings from the valve the gauge came with.
I went through Hell trying to get an original for my MAC Tools compression gauge (with hose). The Shrader valve blew in it and most common replacements would give me low readings. The other mechanic at the shop just happens to have an identical MAC Tools gauge to mine. I kept learning about different Shrader valves and finally found the right one that would match numbers to a known good gauge.
Keep this in mind when playing with compression gauges.

Depends on what oil, how much, and other factors. There are no hard and fast rules and too many variables to strictly say that the engine is junk just from a wet compression test, performed by somebody else.

Hose length will make a difference. A simple calibration in the gauge will not cover all situations, it would read normal on small engines, and high in automotive, or vice versa.

The volume of the hose between the schrader valve and the piston effectively increases the combustion chamber volume, on an engine of larger displacement, it doesn't make much of a difference, but on a small engine, those few extra CCs do. For small engines, you need a hose adapter with the schrader placed right about where the spark plug electrode would be, hose length after the schrader has no affect, will just take more or less pulls to get a peak reading.

How is the hose length going to affect a wet vs dry compression test.

Ive studied automechanisc and have worked on engines all my life and never heard ant talk of what type of oil to use other than simply motor oil.

The oil I used was even lighter, probably about 10wt machine oil.

If you dont have this oil/oiler, get some.


The empty bottle and extendible spout make this a great tool to prime and engine for a quick start and to check and eliminate fuel delivery issues.

Extend the spout, squeeze the bottle then put spout into container of gas and let it suck gas out of tank. You now have a couple ounces of fuel to prime an engine, light a fire, soak your sneaker with. :shock:

It doesn't. That was only in regards to getting accurate readings on small engines.

I'm not saying compression isn't your issue, but those numbers aren't far enough out of the norm for me to be overly concerned.

Normally you have either a loss of compression on one cylinder, or in the case of low compression all around, the engine would be extremely difficult to start, and run okay when the RPMs are higher, where air doesn't have the time to bypass a failed sealing component.

This outboard has the turntable under the flywheel where the whole ignition system rotates to advance the timing correct? Is all of that working properly? How about the rubber roller on the throttle cam?

 

[RaisedByWolves]

Yeah it all looks good.

It was literally fogged and put up, then pulled out 15yrs later and here we are.

I’ll admit that nothing makes sense, but I disagree with low compression motors “always” being hard to start.

Harder to start? Sure.

Pull your hair out hard? Not always.

 

[user 21074]

Are running J6C plugs or the J4C?The one I had already had the J6C"s in it.So when you did a link and sync on the carb. the roller is hitting mark on cam as the throttle plate just starts to open?Did you look at Leeroys ramblings?He talks about removing the 1/2" core plug to check the holes in the carb body.http://leeroysramblings.com/OMC_9.5.htm

 

[Pappy]

I don't want to take this thread off track but the comments on compression gauges and hose length and shrader valve location is a bit bogus.
Shrader valves are located at the spark plug end of the hose. As the engine is turned over the valve opens and the hose is filled with the compressed air from the cylinder. The valve then closes and opens again with the next revolution. Eventually the hose comes up to the same compression as the cylinder and a correct reading will end up on your gauge no matter the cylinder volume (big engines vs small) That is simple physics.
To put this in another simple way. Think of a compressor with a shut off valve for the working lines. Pick a shut-off pressure (lets say 125 psi) Whether the line is 25' long or a mile long eventually that compressor will do it's job and fill the line when the shut off valve opens the lines to tank pressure....just takes a bit longer. The gauge on the compressor will reflect this.....same as a compression gauge.
Common sense prevailed in mentioning the addition of oil We are in a 2-stroke forum and the addition of 2-stroke oil to a cylinder to check for ring leakage is the norm. If the rings already have minimal leak down and blow by then the only way you are going to get a huge increase in compression with the use of ANY oil is to add such an amount as to effectively increase piston volume. Doing so may damage the engine. Again, in this forum common sense prevails.