1967 Mark Twain V-sonic

I just aquired a 1967 Mark Twain v-sonic with a 1968 100 hp Merc 1000 Tower of Power 6 cyl hanging on the transom, and a 1966 Johnson 100hp v4ml 12r as a spare. I would like a few expert opinions on these motors as I have not dealt with anything this large before. Was also wondering how much smaller a motor I could step down to. I have a 1963 40 hp Johnson, and a 1973 50 hp Evinrude. I'm really not to concerned with running to much over 30 m.p.h.. Any thoughts? Also, how good are these two particular motors?

Re: 1967 Mark Twain V-sonic

Before we can suggest a smaller motor you'll have to tell us what a Mark Twain V sonic is ;size weight style,material?
I can't speak specifically to those particular motors.But generally the Mercs are more difficult to work on and parts somewhat more scarce.
Some of the old ignition parts for both brands are scarce and expensive. Again can't be specific.The Merc has 3 individual carbs,the Johnson has 4 individual carbs included in a single assembly.When assembled correctly idle mixture can be adjusted as a unit the Mercs are individual.
The Johnson has one fuel pump the Merc may have 2 or more fuel pumps.
You may want to look up routine parts for each motor.

Re: 1967 Mark Twain V-sonic

I have two 1969 Merc 1000s and one 1967 Merc 950. They are very good engines if they are in good shape. Lightweight powerfull n' real purdy too!!!

Ya need to check the LU to make sure the 90 weight marine gear oil has no water in it. Good idea ta change.

Put muffs on her and fire her up. Make sure she has pee from the tell tale, (ya need ta drop the LU to change the water pump impeller which would be a good plan).

She has two fuel pumps on the starboard side of the block, (easy ta change diaphrams). Make sure the fuel lines don't leak, (if so replace). There are three filters on top of each carb ya may need ta blow out.

Ya may wish ta unscrew the distributor cap n' inspect n' clean don't remove the rotor, (ya can't). Don't pull wires from the cap (they are screwed in).

All the ignition parts carb R & R parts wires n' plugs are available. The engines don't like salt so much, (mild steel driveshafts).

Mine will run for another 40 years (easy) and they have never been opened up.

Dunno much about the bigger Johnnyrudes, Methinks they were also good engines 'cept the 'lectric shift was a bit of an issue.

OH one more matter: the Merc will run away from the ol' Johnnyrude if speed n' power are a cornsideration.

Me overpriced $.02. JR

Re: 1967 Mark Twain V-sonic

Sorry for not being more clear, I assumed that anyone replying to this post would be a Mark Twain enthusiast, the boat is a 16.5 foot fiberglass semi-v. the deck and transom are very solid. The vinyl and carpet will need to be replaced. Otherwise the boat is in great condition for its age.I'll post photos.

Re: 1967 Mark Twain V-sonic

Here's me and mine about a hundred years ago



Great starter boat with a 115 tower - Heavy for her size though and she'd run around 40-42 spedo - no GPS in those days. I'd stick with at least 100hp as the trihulls aren't known for their speed, or ride for that matter. Good luck with her.

Edit - just noticed you stated V, not Tri Sonic. The Twains were known to be fairly heavy boats though.

Re: 1967 Mark Twain V-sonic

That it is mate! Nice boat in the photo.