What Dinghy Outboard to Buy

[SomeGuyInaShirt]

Okay so it looks like the general consensus is that I should buy a small outboard motor but which one?

Looks like a Mercury 3.5 is a nice combination of low weight, and enough power to plane with a catamaran dinghy and I thought because it is made by Tohatsu in Japan that it would be reliable but it sounds like this is not the case. I can't get gasoline without ethanol in Canada and don't have the patience to remove it myself. I would run fuel stabilizer in my fuel and do preventive maintenance, should that not solve the reliability issues? Seems like carburetors contaminated with fuel residue is the primary culprit. I guess since I'm going into developing countries I'll carry a spare carb and all the usual maintenance items. Can any of you recommend a better option? I like the Merc. 3.5 especially because it can be modified to act as a 5hp with a larger carburetor but maybe older outboards are more reliable?

[Tin Tin]

If you modify it to use an external tank then you will obviously not need to fill up as much and have much greater range without needing to carry a spare fuel jug. In addition you could install a fuel water separator/filter just after the tank and this will reduce most fuel problems. Also with an external tank it can be disconnected and used as the carry can if needing to walk any distance to a gas station.

See

https://www.youtube.com/watch?v=ycVFv1A4oU0

[Tortuga's Lie]

I don't think it will matter which engine you buy, they all will be subjected to fuel issues, unless you can get a small, direct injection engine without a carb. The best preventative maintenance you can do for your outboard when it comes to fuel problems, is to shut off the fuel while the engine is running and let the fuel burn out. Do this if you are not expecting to use your engine for a couple of days. If you know you are not going to use it for more than a week, do the same but when it dies out, drain the bowl of the carb. If you stick with this methodology, your fuel problems will be greatly minimized unless you get some really crappy fuel. Oh, and always use a fuel stabilizer.

[SomeGuyInaShirt]

Nice to see this is an easy modifications to make. I was previously told by representatives at onlineoutboards.ca that the Tohatsu outboards came from the factory with fittings for an external tank but maybe they deleted it in recent years. Definitely nice on long rides.

[SomeGuyInaShirt]

Good advice. I just hope the manual that comes with the outboard is more in-depth than the one that came with my inboard; sounds like outboards require frequent surgery from the get-go.

[Pete7]

Are these two or four stroke Mercs you are looking at?

The Tohatsu/Evinrude/Johnson/Merc/Mariner 3.5 2 stroke engines are reliable. We had the white Evinrude version for a long time, about 15 years. Had to service it once with a new plug and impeller and that was it.

However, be aware that separating the lower leg can be a pain if it hasn't been done previously with a liberal dose of grease applied to the gearbox to engine bolts. You must do this before it starts to get old or you will regret it.

Next, assembling it needs some time and skill to align the drive shaft, water pickup and gear selector whilst holding the leg. You will need four hands of which at least two need to be the size of an 11 year old.

Given that petrol in the UK now has green plant juice added, we swopped the 3.5hp for a Honda 2.3hp. No water pump or galleries to flush as its air cooled. Spares available world wide through any Honda car or motorbike dealer.

Would like an electric outboard, but the Honda just keeps going on and on. Seems pointless to change it as its a dead simple little engine.

Pete

[rslifkin]

For external tank connections, the Tohatsu / Merc 2.5 and 3.5 4 stroke don't have them. The 4hp and larger do have external tank connections, even on the models with an internal tank.

[Bill O]

Haven't looked at the specs for Tohatsu based 4 stroke motors (includes Mercury up to ~40hp) in a while, but do not think you can put a 5hp carb on a 3.5 and have it to work properly. The motor bases that could swap carbs were the 4, 5 and 6 hp series. They all weighed ~55lbs.

Just sold a Tohatsu 3.5B (2 stroke w/fwd and neutral shifter) last year that was a very solid light weight motor (~29lbs). Easy to handle w/o a motor davit.

We have a 12' inflatable minicat and the 5hp (2 stroke) moved it along very well w/2 people and some gear (~400lbs). Never tried the 3.5, but the 5hp could get the boat up on plane w/a little more throttle left over. We've moved up to the max hp for the minicat w/a 9.8 2 stroke to be able to do more pay load (people/provisions) over further distances.

You really need to determine how you will use the dinghy/motor and if motor weight matters. If you are just using it around the anchorage a 3.5 would be ok, but if you want to explore much further would think a 5hp with a remote tank would be better. I prefer 2 strokes since they are much easier to maintain and aren't too finicky about fuel.

[Tsuru]

One of the problems with small outboards is that they have small carburetors with tiny jets. Our experience with a 2 Hp Honda is that if we used it regularly, even with Ethanol fuel it ran fine. If we did not use the outboard for a while (say a month) the jets started to foul and the carburetor needed to be cleaned. I got in the habit of running some non ethanol fuel through the tank and then running the tank empty when the motor would not be operated for a couple months. This seems to have solved the problem and I use the same procedure today with larger outboards. We also add fuel stabilizer. I carried a carb gasket set but don’t think I ever needed them, just reused the old.

[Shrew]

Keep in mind that most of the OB's under 15 HP are all made by Tohatsu. Just something to consider.

[rslifkin]

Originally Posted by Shrew

Keep in mind that most of the OB's under 15 HP are all made by Tohatsu. Just something to consider.

Yamaha, Honda, and Suzuki all make their own as far as I know. Merc 4 strokes up to 30hp are Tohatsus (and big Tohatsu 4 strokes are Hondas). The older Nissan branded stuff is all Tohatsu as well.

[Jammer]

Originally Posted by SomeGuyInaShirt

I can't get gasoline without ethanol in Canada

This isn't as big of a deal as some people make it out to be. Buy small amounts of fuel often. Keep it clean, cool, and in a sealed container. If you have stale gas, dispose of it. Eventually you will have problems whether you have ethanol in your fuel or not. Clean or replace the carb when it happens.

Can any of you recommend a better option? I like the Merc. 3.5 especially because it can be modified to act as a 5hp with a larger carburetor but maybe older outboards are more reliable?

There are tradeoffs. Among 4 strokes, the Yamaha motor in this size range is reliable but heavy. The Suzuki one appears to have a uniquely serious problem with corrosion of the cooling water passages when used in the ocean. The Honda one is air cooled, loud, and has a limited maximum lifespan but doesn't have the maintenance associated with water cooling.


I have a (much) older Johnson 3hp that I use on my dinghy. It uses almost twice the fuel of newer motors but is much smoother as it is a two stroke, two cylinder machine. It's OK. My brother has a Suzuki 2.5 that he likes but he only plans to use it in fresh water.



For most dinghies 5 hp will not go materially faster than 3.5 hp. Fwiw.

[Jammer]

Originally Posted by Tortuga's Lie

The best preventative maintenance you can do for your outboard when it comes to fuel problems, is to shut off the fuel while the engine is running and let the fuel burn out. Do this if you are not expecting to use your engine for a couple of days. If you know you are not going to use it for more than a week, do the same but when it dies out, drain the bowl of the carb. If you stick with this methodology, your fuel problems will be greatly minimized unless you get some really crappy fuel. Oh, and always use a fuel stabilizer.

Advice varies. I currently believe that letting the fuel burn out doesn't help, and I currently believe that fuel stabilizer doesn't help much. I've used these things in the past.

[Jammer]

Originally Posted by Tin Tin

In addition you could install a fuel water separator/filter just after the tank and this will reduce most fuel problems.

The water separators are not effective on fuel that contains ethanol.


The filter part will still remove solids. Every outboard I've taken apart (except for an Elto Ace that was built in 1939) has some sort of filter inside the engine, though, so you may be duplicating what you already have.

[rslifkin]

Generally when it comes to small engines, I stabilize any fuel right away at purchase (to reduce worries about using it up quickly). If running non-ethanol, an occasional splash of iso-heet to make sure no water is accumulating somewhere in the system, waiting to bite when it gets filled with E10 gas later.

If it's going to sit for more than a week or 2, fog it so the inside of the carb is nice and oily. That seems to avoid some of the corrosion and gumming problems that frequently happen.

I don't generally worry much about the age of the gas as long as it's in a modern, well sealed can or tank and has had stabilizer added. Gas won't last as long in an old school vented tank. I run yard equipment on year old gas frequently at home with no issue (lawnmower and snowblower get stored with full tanks for the off season). I expect no issues with the dinghy outboard when I fire it up in April with the gas that was in the tank from last fall (plus some fresh stuff to top it off). Same goes for the (much bigger) gas inboards in the boat with fuel in the tanks from last fall.