Best old 20hp based motor?

[RathaBsurfin]

Hi yall, im new, and I have a little wooden runabout that I built and I am looking to repower. I have what i would condsider a good amount of experience in old motors, but I want something unique and powerful to push my boat. I have been looking for a Mark 20 to hop up, but i havent really found my dream motor yet. Ive extended my search to later model black mercurys but yall seem to have a lot of knowledge so Id like to hear what you think. Also where is a good place to find one? I am a member of the antique outboard motor club, and have bought several motors through them, but they arent very active in my area. Ebay motors seem to be going higher than what I want to pay. So what else should i look for? Its a 1/4" plywood on mahogany frames, about 11' long. for FYI, i also have a built and bored out '77 johnson that was built by an old racer on a 1968 whaler. neither are performance boats, but i love old outboards and I really have enjoyed the discussions and pictures in this section. thanks yall

[crazy horse]

I think one of the best were the early seventy Merc's. I run across them from time to time. I even have a 1974 low hours eletric start short shaft that needs a case. I just don't have a boat to put on it on right now or I'd pick up a case on ebay. Ebay can be good for parts but those engines go for WAY more than you can buy them locally. The earlier Mark engines were great but the parts are gettin a little high for me. My first Merc was a Mark30, That engine ran great. I still have three.:D

[RathaBsurfin]

yea, i think the marks are gettin a little high for me too. Ive seen some that arent priced bad but the shipping would kill me. I guess ill start lookin for a later model black model. Is there anything available performance wise for a 20hp mercury of that vintage or is it pretty much dependent on my creativity? thanks

[Chinewalker]

Try this link and see if you can get an idea or two...:
http://www.pfs-ware.com/kwast/heard_of_a_canadian_rat_racer.htm

- Scott

[RathaBsurfin]

thanks for the link, those are really cool. I have a few motors to play with, more like 7, but none of them are above 10 horsepower. I think I am going to search for one of those skinny black mercs to play with. I bet I could make a set of stacks for it, shave the head a lil bit, find a prop. Is there anything you can do about the carbs? Can the jets be drilled out? I guess ill probly need to research and ask these questions when I find one.

[Mark75H]

You can't "shave the head" on an old Merc .... they are cast on

You can drill the jets out if you want to, but it is easier to find the older carbs with the external adjustable main jet. Or convert the fixed jet carbs to adjustable.

The 22 cubic inch Mercs use the larger "KA" series carbs. Since you are just playing, I'd suggest you consider using a 22 ci motor anyway. If you want to put a KA on a smaller motor you can fill in the original stud holes and redrill and tap new holes to mount the larger flanged KA carb.

Most people figure out the external pieces for tuned exhaust and find the piece between the ports and side plate a harder puzzle, but I think I've learned how to make the piece they call a "filler block" with a little less effort. Instead of machining one piece to match the 3 different surfaces of the block .... machine 3 pieces and bolt or weld them together.

[RathaBsurfin]

thanks mark, thats good information. Looks like I have a lot to learn.