I have been working on this new to me 1975 Evinrude 25 (25503B) recently. Compression numbers were 124 top/118 bottom and it fired right up once I got it home, so I decided it was worth a little work to get back on the water. Unfortunately when I finally took it out for a boat test, I was getting some pretty bad thumps from the motor.
Here's a couple videos that show what was happening:
http://youtu.be/AI9u_jTz438
http://youtu.be/HacPYde5Pxo
That was nowhere near full throttle, I was just revving it out slowly when it started acting up
I thought it might have been jumping out of gear, so I held onto the shift lever, but that didn't make any difference nor did I feel anything through the lever while it was going on. I would have thought that the engine would rev when the lower unit jumped out of gear, but as you can see it actually lugged and then ran rough a bit. This had me consider that maybe I had blown a head gasket instead and was getting some water in the cylinder under heavier loads.
Service I had just performed included (all OEM parts) new points set at .020, condensers, spark plugs gapped to .030, carb fully stripped, cleaned & rebuilt, fuel pump rebuilt, water pump w/ housing replaced, thermostat, thermostat gaskets, lower unit pressure tested (and passed), and lower unit lube changed. Motor was running great in the test tank, but this was the first time I had it out under a real load.
When I got home, I drained the lower unit lube and it was pretty dark like syrup, much darker than I would have expected from a 0.6 hour test run (I have an hour meter). I am letting it sit to see if it separates and I got any water in there.
I pulled the spark plugs (with 0.6 hours on them) and this is what they looked like. Top plug on top, bottom plug on bottom:
The bottom plug does have a bit of that 'steam cleaned' look, so I think something is going on in the bottom cylinder.
I did a compression test and was surprised with the results... Still 124 up top, but now 140 on the bottom cylinder. I didn't really know what to make of that.
Was really a bummer of a test, this thing had been running great in the tank. Thoughts? Bad lower unit and head gasket blown, or something else entirely? Suggestions what to check next?
Thanks
Here's a couple videos that show what was happening:
http://youtu.be/AI9u_jTz438
http://youtu.be/HacPYde5Pxo
That was nowhere near full throttle, I was just revving it out slowly when it started acting up
I thought it might have been jumping out of gear, so I held onto the shift lever, but that didn't make any difference nor did I feel anything through the lever while it was going on. I would have thought that the engine would rev when the lower unit jumped out of gear, but as you can see it actually lugged and then ran rough a bit. This had me consider that maybe I had blown a head gasket instead and was getting some water in the cylinder under heavier loads.
Service I had just performed included (all OEM parts) new points set at .020, condensers, spark plugs gapped to .030, carb fully stripped, cleaned & rebuilt, fuel pump rebuilt, water pump w/ housing replaced, thermostat, thermostat gaskets, lower unit pressure tested (and passed), and lower unit lube changed. Motor was running great in the test tank, but this was the first time I had it out under a real load.
When I got home, I drained the lower unit lube and it was pretty dark like syrup, much darker than I would have expected from a 0.6 hour test run (I have an hour meter). I am letting it sit to see if it separates and I got any water in there.
I pulled the spark plugs (with 0.6 hours on them) and this is what they looked like. Top plug on top, bottom plug on bottom:
The bottom plug does have a bit of that 'steam cleaned' look, so I think something is going on in the bottom cylinder.
I did a compression test and was surprised with the results... Still 124 up top, but now 140 on the bottom cylinder. I didn't really know what to make of that.
Was really a bummer of a test, this thing had been running great in the tank. Thoughts? Bad lower unit and head gasket blown, or something else entirely? Suggestions what to check next?
Thanks
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