2003 25 hp merc 2 stroke impeller replacement

nola mike

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TL;DR : how do I drop the lower unit to change the impeller? Looks like the shift shaft is holding it on. Manual says disconnect the linkage near the cable, but on my remote shift model that doesn't release anything.

Long version:
My boat found a crab pot. Couldn't figure out why it would stall instantly when putting it in gear. Like, it really took me longer than it should have. Untangled and went back to shore (not far). Today fired it up and seemed to be running fine. Looked back and saw no tell tale. Throttled back and engine started smoking. Shut down. Anyway ... Realized that I don't think I've changed the impeller on this thing in the 7 or so years since I've owned it.
 

flyingscott

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The shift linkage disconnect is behind the electric starter. Take the starter off and you will see it. When you reassemble it make sure the washer goes back on the shift shaft.
 

nola mike

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The shift linkage disconnect is behind the electric starter. Take the starter off and you will see it. When you reassemble it make sure the washer goes back on the shift shaft.
Thanks! Got it off, remembered the washer, then forgot about it 2 minutes later, somehow found it in the sand. I think I might have narrowed down the problem ;) Strange that this happened immediately after wrapping up a crab pot, can't think of anything other than coincidence... Waiting on the new kit to get on the water for the weekend .
IMG_20220815_142435.jpg
 

racerone

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Still lots of folks out there who do not install a new impeller every 5 years.----Typical to see that damage.-----Compression test must be done.----Post the numbers.
 

nola mike

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Still lots of folks out there who do not install a new impeller every 5 years.----Typical to see that damage.-----Compression test must be done.----Post the numbers.
Yeah, hopefully no damage. What numbers am I looking for?
 

nola mike

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Yeah, hopefully no damage. What numbers am I looking for?
Ok, got everything back together. I'm sad to say that the compression was 65 psi in both cylinders cold. Didn't do a wet test or retest after it was warm. I'm happy to say that it was running normally with those numbers. Top speed was 27-28 mph, which might be down a hair since I purchased the boat, but not by much. I'm sure my timing is off, but haven't been able to get a reading with my timing light for some reason (I've never dynamically timed a 2 stroke before, so not sure if it's an issue with the light)
 

flyingscott

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Ok, got everything back together. I'm sad to say that the compression was 65 psi in both cylinders cold. Didn't do a wet test or retest after it was warm. I'm happy to say that it was running normally with those numbers. Top speed was 27-28 mph, which might be down a hair since I purchased the boat, but not by much. I'm sure my timing is off, but haven't been able to get a reading with my timing light for some reason (I've never dynamically timed a 2 stroke before, so not sure if it's an issue with the light)
Your gauge is broke. No way that motor runs with 65 psi of compression?
 

nola mike

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Your gauge is broke. No way that motor runs with 65 psi of compression?
Runs, and runs well. Used the gauge a couple of weeks ago on my 4.3 and it was 150 x 6. Like I said, cold engine. Maybe these 2 strokes are sloppier than the 4 strokes. I didn't really care since it was running well, but now my interest is piqued. Only reason I didn't retest was because I didn't know of a good way to disable the ignition (I disconnected+ from the coils before). Guess I could either pull start it or jump the starter with the ignition off. I really need to figure out how to set the timing on this thing.
 

flyingscott

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Leave the timing alone. Unless someone adjusted the link your timing is fine. And either your gauge is broke or you did a faulty compression test. No way that motor runs with 65 psi.
 

nola mike

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Leave the timing alone. Unless someone adjusted the link your timing is fine. And either your gauge is broke or you did a faulty compression test. No way that motor runs with 65 psi.
Everything has been screwed with in there. I want to set everything up fresh--throttle/shift cables, idle, timing, fast idle, etc. Nothing works quite right. Mine doesn't appear to have the same timing link setup that some of the other engines have. Mine has an idle timing screw and a running timing screw. As for the compression, dunno what to tell you.
 

Scode68

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I have a 1995 20hp and the factory manual says 150-180 psi. It also notes that if the compression is below 120 psi then there will some serious wear on the engine.
 

flyingscott

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I have a 1995 20hp and the factory manual says 150-180 psi. It also notes that if the compression is below 120 psi then there will some serious wear on the engine.
Maybe for a 4 strk. A 2 strk Merc motor will never pull those kinds of #s. A good healthy 2 strk 20/25 will be around 120 psi. My rebuilds don't pull much more than 120.
 

nola mike

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Maybe for a 4 strk. A 2 strk Merc motor will never pull those kinds of #s. A good healthy 2 strk 20/25 will be around 120 psi. My rebuilds don't pull much more than 120.
Took it out today with the kids, 22 mph cruising, 25 Max. Checked compression when I got back...65 psi. Waiting on 2 stroke timing light.


Here's a pic of the linkage :
IMG_20220827_121008.jpg
IMG_20220827_121000.jpg
 

Scode68

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Maybe for a 4 strk. A 2 strk Merc motor will never pull those kinds of #s. A good healthy 2 strk 20/25 will be around 120 psi. My rebuilds don't pull much more than 120.
That was taken directly from the Mercury service manual 90-826883R2 JUNE 1998. It covers 20 & 25 2 strokes from about 1994 1/2 and later.
 

flyingscott

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That was taken directly from the Mercury service manual 90-826883R2 JUNE 1998. It covers 20 & 25 2 strokes from about 1994 1/2 and later.
So put up a motor actually pulling those #s on a compression test. And a copy of the page.
 

nola mike

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That was taken directly from the Mercury service manual 90-826883R2 JUNE 1998. It covers 20 & 25 2 strokes from about 1994 1/2 and later.
I'm not able to find that in there
You can use a timing light designed for 4-stroke, however the RPM-reading will not be correct!! for that you will need a secondary (cheap handheld)
That's what I'd think. However the timing mark remained static no matter what I did with the advance on the light (2 different lights). Bought a new one that's supposed to work with a2 stroke, but I can't see how it would be different. Going to have another crack at it next weekend. Doubt a video would be able to capture it.
 
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