Merc 25SS Info needed

[ram95]

Can anyone tell me where I can find some literature on this engine? The Merc dealers just look at you funny-like when you ask about it. But, I'm used to that. Jet sizes and max spark advance would be good for starters. And, if anyone has a top main bearing cap (this one has two broken ears).. I could use one of those as well. Thanks!!

[ZUL8TR]

[What year engine is this. 22 ci i suppose? I have a 25SS from 1974 vintage that I used to race in that class in 25SS hydro.

[swheeler]

You should be safe to time the engine to 33 degrees which is .208 inch before top dead center. You might be able to time higher but that would depend on your fuel, spark plug heat range, and carb jetting. If you are not racing I wouldn't get too aggressive. I've been running an adjustable jet in mine but am planning on switching to a fixed jet. My engine has a megaphone and because of this I'm going to start with a .071 jet which should be rich and go smaller until I hit the right one. I think I will likely end up around .063 to .065 but richer is always safer. I can't help you with the end cap but I did see a 25ss that had a reinforcing plate made that sat on top of the end cap around the mount flange. A flat head bolt replaced the hex bolts and was counter sunk into the plate. Maybe yours could be saved with something similiar. Also be aware that the newer engines had a different end cap then the older 25ss due to a difference in the way the ignition mounts. Hope this helps.

[ram95]

25ss info

Thanks very much for your help. I'm familiar with the 4cyl mk55/58's and magneto ignitions, but the 25SS has been a stranger up to now. I'll keep the numbers you gave me in mind as I get it ready to run. I'm not sure what approach I'm going to take with that end cap - what a marginal design. I'll be checking the local dump for that one, and at the same time I'll be eyeballing how to make a retainer plate like you mentioned - I like that idea!

[alanaker]

25ss

Alex- Check over at Lincolns' shop. I bet he has those parts.

Alan

[ricochet112]

I'm fairly certain I have an upper end cap for one, Ill check.

[ZUL8TR]

25ss info

For the stock 25ss 1973 engine that I have the timing recommendation from the factory was 38 degrees BTDC
(I used to set it with a depth gauge but I don't recall the conversion reading in decomals of an inch). This engine is 21.9 c.i. and rated at 6600 rpm and has 16:21 gears. I used to run it with Champion L61Y plugs at 6900 to 7100 rpm depending on prop and depth of the lower unit torpedo which ranged from 1/2 to 3/4 inch below bottom depending on water and wind conditions of the course. Speeds were in the mid 60's on my hydro set for competition. Were talking APBA rules 1975 thru 1979.

[trident]

38 degrees would be .285"... Factory OEM carb jet for KC16-A is .061"

Hope this helps.