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25hp or 20hp Mercury

T

twizzle

New member
"Hi, I have a 25hp mercury &#4

"Hi, I have a 25hp mercury (5826772) which I have been running up and down the river on for the last 3 months but I don't know the age of the engine and it struggles (splutters/ stalls) at higher speed. So I bought a 20hp (9473093)for next to nothing, for spares - but this engine runs - I think the 20hp is more modern - so which engine would you use?
On the 25hp I am in the process of changing the fuel line to 5/16 and a new primer bulb, and the carb hoses as they have a bore of only 2mm - the bottom hose keeps being blown of the nozzle at the cylinder end- I don't know why? I have also changed the trigger unit and sparkplugs which immediately improved running.
Any comments would be appreciated."
 
"Andy, there isn't much pe

"Andy, there isn't much performance difference between a 20 and a 25 to start with (maybe 2 mph difference on any given rig).

The 25 horse is a 1981 model - decent motor, T4 ignition (so same as all the small outboards up to 2005) but it does sound like the carb is in need of a rebuild. The 25 horse was mechanically the same as the 18 horse (except the carb) - the 20 was a different model all together so not the best "donor" motor for parts (although all the ignition parts should swap back and forth).

The 20 horse is a 1987 model built by Merc in Belgium. Since it's a post-86 motor it is totally "modern".

If the 20 is running nice, I would use that and tinker with the 25 - both are excellent little motors, but in terms of "on boat performance" you would be hard pressed to tell the difference between the two of them.

I would have no issue hangin' either one of those motors off the back of my rig - hey, if you don't want one of them, you can send it my way
"
 
"Hee, hee! Graham's alway

"Hee, hee! Graham's always trying.....

I believe the carb and possible the tuner are the only difference between a 20 and 25 Merc. The 18 has smaller ports and a very restrictive tuner--that I know.

Jeff"
 
"Thank you Jeff and Graham for

"Thank you Jeff and Graham for replying, I will be trying the 20hp out in the comfort of the shed at the weekend! As you have given me the age of the motor I will try and find the spec for gapping the new plugs.
Thanks again"
 
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