Honda 5hp Outboard - Breathing difficulty?

[dlf]

I have a 12 year old Honda BF5 short shaft outboard engine that is causing me problems at the moment. The engine runs fine when the cover is removed but as soon as I put the cover back on, the revs drop off gradually but fairly quickly, until the engine cuts out. I have checked the air intake of the carburettor and I have cleaned some of the muck off the wire gauze that covers the intake. However, before I completely disassemble the carburettor, I wanted to check that I was looking in the right place for the problem. As you may have gathered I have very little knowledge of engines but I would like to try and resolve the problem myself, if I can. If not I will have to dig deep and get an outboard engineer to repair it at some huge expense.
Can anyone help?
Thanks

 

[Lakesailor]

I had the same engine. I seem to remember talk of this problem due to an exhaust leak venting inside the cover and literally choking the engine.
I seem to remember it was cause by a failure of a casting. Can't be more specific.

However. You asked the same question 4 years ago and got told a wide variety of answers then.

 

[VicS]

If the engine runs Ok with the cover off there is not likely to anything wrong with the carb so don't mess with it. Especially with little knowledge.

Very probably as LS says there are exhaust gases leaking. When the cover is on it traps the gases and the engines suffocates on its own exhaust.

Do however check how fresh air is admitted .If there is any sort of grill it could be choked with debris. Very unlikely but it would be silly not to check

Not in a well? outboard wells can often trap the exhaust gases and lead to this sort of thing

 

[alan]

Honda 5HP Outboard

The answers you have already received are probably your best bet .... but just in case, the cover on the Hondas is very tight to the spark plug HT cable. Could it be that the cover is pushing on the cable and has caused a fracture??? A long shot but ...?

Alan.

 

[paulferris1964]

Is it in a well? Had the exact same problem with my Honda BF5. Mechanic told me its a known fault, where exhaust gases escape and suffocate the engine. Outboard worked fine on the rail, but not in a well. Sold it and bought a Tohatsu 6hp. No such problems.