Friday, 27 April 2012

How to service a British Seagull outboard motor

British Seagulls date to 1931, they made around 2000 a month at one time, so we may have about 100,000 out there now, does anyone know this?
Note: one web site suggests a million made due to the war effort?

In my case I have been gifted a not so old one, the one in question is the LLS model and dates to 1961, they have an engine number on them, find that then search the web to find out its age.

I was ready to start after a degrease with water soluable cleaner, then a wire brush session to remove dirt and old salt deposits, a second water soluable clean up and wash down with the hose pipe again has the motor looking quite smart. In my case I was able to use an air line to blow the water off, you may find just using a clean cloth and spare paint brush does much the same.

Any service must start with the spark plug, they are made by Champion and marked D16 the gap needs to be set at 0.020" thousands of an inch, this one was closer to 0.040 thous, this will change the timing and change the way the motor runs. If you have no spark you may find the points are dirty, or if the engine has not been run for a very long time, the magnets in the flywheel need a recharge, check out at the SOS web site for information on how to attend to both the points and a recharge of the magnets. 

The same spark plug after it was bead blasted and the gap set to 0.020"

These parts were in a bad state, years of none use had seen them age and become more or less jammed up, in the case of the gear box pinion, it was seized solid and I had to ask the advice of John from SOS In Essex, England on how to free it up.

SOS and the contacts for John in the UK are in the link above.

Johns phone number in the UK.

The gearbox house and gear wheel, with the shaft came out after a bit of carefull  work, once cleaned up, it was clear to see that they were still in fine condition and still able to do the job they were made for.

Most of the parts taken off the engine were cleaned in the blasting cabinet, I did not do the Villiers carb due to the fact that the small glass beads may do more harm than good.

The seized pinion, Johns advice was to add lots of thin oil and use a battery powered drill turn the square drive that is in the house, in my case I needed a 220v drill but I used minimum power. The shaft freed off just as John had predicted, I then added 20W/50 engine oil once the shaft was free and moving. Any friction here will stop the engine from turning as it should.

A moment of triumph when the British Seagull Century starts as it should and on the second pull of the rope, there after it would start on the first pull every time.

How hard can this be!


I spent more than a little time reading up on what needs to be checked on a Seagull motor to ensure it will work, there seemed to be no doubt it would work, even though my motor is fifty one years old.

The list and excepting the seized gear box pinion.

Clean the fuel tank, fuel stop fitting, there is a filter in the original ones., also one will be found in the banjo union fitting to carburetor. Clean the tank filler knob and fuel line, my fuel line was thick with a dry black sludge. Strip the carburetor and ensure its clean and the needle is straight and slides easily, in my case I need a new throttle cable, as the slide will not close, you may need a new spring that fits the slide also?

Adjust the spark plug, make sure its the correct one, test the spark by spinning the flywheel, use a 4mm line and only three turns around it, I made up a pull handle from some 22mm dowel with a 6mm hole through it.

The details are what makes the difference? this Champion spark plug cap is from the right period, its from a Jaguar 3.8S type. It is not wateproof, you could use the one the NGK make for motor bikes, part number LB10F 8358 (black) it is also a resistor type, which may be a good idea.

The gear box needs to be clean, it also needs some 140EP grade oil in it
in my case I have yet to find that grade and have used Castrols 90EP grade made for outboard gear boxes, it will see very light use for a while so should do the job for now.

Mix the correct petrol (gas) to marine outboard grade two stroke oil, thats 10:1 and should be done with unleaded petrol. Do not use fuel older than three months old, the modern stuff can go off after that time, you will notice a foul smell when its gone off.

Starting, open the petrol tank vent screw a half turn, check the tank and unions have no leaks, mine did, I fitted new fibre washers, I could then close off the choke on the carburetor, apply full throttle, make three turns of the pull line around the flywheel and see if the Seagull Century would fire?

Pull one and nothing happened, do the rope thing again and give it another pull, the motor fired and was a runner! Now open the choke and close the throttle as required.

Note, the two breather holes in the large stainless steel tube should face backwards, I have put the tube back side on and  incorrectly!

One last item and this is very important, as soon as your Seagull is running, check the cooling water escape hole has a steady stream of water running as can be seen in this picture. If there is no water, stop the engine and find out why? To stop the engine, close the throttle and the fuel supply tap and put your hand over the carburetor intake.

All photos by R McBride using a Canon G11 camera.

New tank transfers are available from SOS.

We have a British Seagull for sale, its a 1973 model and has a gear shift. Available as is, or fully restored to your order. contact me via

Roy  @

Some updates have happened since this Seagull repair page was posted, find them below: