Mercury 4HP 2 Stroke c1986

[Big_Max]

I have recently purchased a Beneteau which came with an old 1986 outboard which is used on the tender. Being an old engine I do not want to spend a fortune on a main dealer service.

Initially it did not work but I have striped down the fuel tank, filter, carb and given them all a good clean. The fuel in the carb resembled golden syrup!

I have managed to get it started but it will only run at high revs for about 5 seconds. It normally takes about 5 pulls to get it started.

Whilst I can't be sure it feels like the 5 pulls prime the system but it then runs out of fuel.

Could there be a problem with the fuel pump ?

How do I check?

Any other suggestions?

 

[VicS]

Make sure you have a good fuel flow to the fuel pump ( tank vent open and clear?)

Disconnect the pump from the carb and pull it over a few times. You should get good spurts of fuel. But I am not sure if the pump pumps from the internal tank or if its only for a remote tank. Is there a connector for a remote tank

If you allow the carb bowl to fill there should be enough fuel in it to run at idle speed for a minute or so. Maybe not for more than 5 seconds at high speed

Check the compression.

It sounds as though the carb is not properly clean but check that you have a good strong spark that will jump an air gap of several mm.

Have you tried a new plug? I think it has points ignition. Have you checked them?

If you do not have one you should be able to download an owners manual from http://download.brunswick-marine.com/download/preparesearch;jsessionid=ds906qmljl4re?lang=EN&mod=4



Is it a Japanese made one ? What's the serial number ? If Its Japanese ignore most of the above

 

[Big_Max]

Thank you for your reply.

The vent is open and clear.

There is no connector for a remote tank just an internal tank. The pump appears to be a small diaphragm type unit with no priming lever.

How can I simply check compression?

The carb seems to be clean. I have cleaned it several times.

The spark plug has been replaced and a good spark can be seen.

There doesn't seem to be a suitable manual on the site Model number 9483203

 

[VicS]

That number makes it a 1987 model. Always useful to know exactly what one is talking about.

Parts lists and exploded diagrams here https://www.boats.net/catalog/mercury/outboard-by-year/mercury-outboard/1987/1004207/carburetor I think!

The manual should cover it.. Also covers 5 hp models and speaks many languages

http://download.brunswick-marine.com/filereader/file/pdf/4/enen/outboard/1998/2-stroke/10102z80.pdf

Ordinary car type compression tester will do the compression test (like everybody has on a shelf at the back of the garage) but if it starts easily not likely to be too bad

Fuel pump is not what I was expecting . Yours looks to be integral with the carb Not so easy to test if you cannot pull an outlet hose off

 

[Big_Max]

Thank you I'll let you know how I get on.

 

[ProDave]

This is very similar to the problem I had with a 5HP Mariner. Tried unblocking everything I could find in the carb

Eventually it was fixed by a dealer, by stripping the carb bare and cleaning it in an ultrasonic cleaning bath. So something was blocked somewhere. Now runs fine.

 

[QBhoy]

If compression is good and carb and jets defo ok...check the coil.

 

[Seajet]

These are very good engines - once you get this snag sorted - but another thing to check is the gearshift lever, which is solid plastic and can seize - feels rubbery and might be snapped if too much force is applied - at the horizontal pivot housing; I drilled an oiling point with tape over it for the rest of the time, problem solved.