Selva 50HP Madeira 684cc MAGNUM Boat Performance Spark Plugs revisited

I wanted to test again Brisk racing spark plugs (NOR14LGS) now that I have upgraded to larger carburetors and lifted the Selva Madeira outboard to the highest mounting position.

I'm comparing against Champion L78 which is one of the recommended spark plug types by Selva owner's manual.

I'm only interested in the top speed gain and after careful testing there was a 0.4 knots difference favoring Brisk spark plugs. This difference is so small that it might be caused by weather, how high the outboard was trimmed and the differences in GPS accuracy.
I also found that my Selva Madeira was not trolling well, the engine stalled many times maybe due to too low RPMs. I raised the idle RPMs to 1200 but when the gear was on the RPMs dropped sometimes below 800 and Brisk spark plugs were not able to keep the engine running. With Champion spark plugs this did not happen.

To sum it up I'm not planning to use these Brisk racing spark plugs because I want the outboard idle and troll properly. Champion spark plugs are also very inexpensive.

Larger idle jets for Dellorto 38/34 carburetors

Recently I installed larger carburetors to my Madeira 40 outboard to match the ones in 40 XS / 50 HP models. Although the carburetors came from Selva factory the idle jets did not match the to specification. What I got was #65 although Selva documentation says that 40 XS / 50 HP models use #70 idle jets.

My Selva Madeira was not idling very well with #65 idle jets although I have adjusted the idle fuel/air mixture screws.

It's not particularly easy to find Dellorto OVC parts online, I noticed that EUROCARB is one of the few who is selling those. Unfortunately they had only one #70 idle jet available and told that they are not getting more. I ordered the one they had and then the problem was to find another one.

When I got #70 idle jet I noticed that it was exactly the same as #65 idle jet, the only difference was the size of the opening in the tip of the jet. I discovered also that number 70 meant 0.7 mm opening.

I decided to convert the #65 idle jet to #70 by drilling the idle jet using 0.7 mm drill bit.
I was not using a drill, only rotated the drill bit slowly until the opening matched the #70 idle jet.
I was extra careful not to leave any metal parts inside and used compressed air to clean the idle jet.

Once I installed these #70 jets to my Selva Madeira 40 it started to run more smoothly, at least I felt so.

From top to bottom:
#65 idle jet
#70 idle jet
#65 idle jet converted to #70 using 0.7 mm drill bit

Installing Michigan Match propeller

I was looking for an aluminium propeller with more than 17" pitch but those are quite hard to find. The propeller must be Selva Madeira compatible which basically means it must be Yamaha compatible. I found a Michigan Match 10.9" x 17.6" propeller for Nissan/Tohatsu and decided to order one.

This seems to be some older model which is not in the latest catalog, the product number is 142009.

Michigan Match 10.9 x 17.6

I quickly noticed that this propeller is not compatible with Selva Madeira stock thrust washer.
I decided to use the Yamaha thrust washer that comes with Michigan Wheels XHS hub kit 117, the one I modified a little.

There was still a problem with the compatibility, the diameter of the thrust washer was about 44 mm or (1 3/4 inches) leaving a 2 mm gap. I really hope someone could standardize the propeller fittings, it's very hard to install propellers from other brands. Of course Michigan XHS and Solas Rubex hub kits are trying to overcome these problems.

What I did is that I took magnetic tape and folded it two times to make a suitable adapter ribbon that was 1 mm thick. I used a bench vice to make it more solid, it was easy to install and after some lubrication the thrust washer installed quite nicely.

I think you can use any strong tape, maybe brass tape could be the optimum, I just had magnetic tape in stock 😏

Magnetic tape

Magnetic tape folded two times.

Custom adapter ribbon installed.

Yamaha thrust washer modded for Selva Madeira.

Michigan Match propeller 142009
ready to be installed on Selva Madeira.

Jun 7, 2018 update:

I tried to install the propeller but diameter of the outer body is too large and the propeller was touching the gear case and only barely rotating!
I'm planning to remove some coating and try again, will post an update later on.

Jun 30, 20180 update:

I used some sandpaper to make hub diameter smaller, now it's a little less than 80 mm and propeller spins freely when installed on Selva Madeira 40.

I did some tests on the water and propeller behaved quite well, still the top speed was a little slower than with Solas 11 x 17 so I'm keeping this Michigan Match propeller as a spare propeller.

14200

142009