Outboard Problems

[Ecosse120]

I have a Tomos 4 HP outboard (air cooled) that has been running fine until recently. On the back of my 22ft boat no problems. Put it on the back of the tender to get home and after a couple of minutes it would start to die but would continue to just about run at full power. Back home on the bench I stripped the carb/fuel filter and have replaced one fuel line (which I though was causing the issue). If I now rev up the engine it drops revs, never actually dies though. If I cover up the air intake a bit it will then rev up again. The only adjustment on the carb is a needle to play with the air/fuel mix. I have now adjusted this and it will again rev. Have I missed something on this and why having run fine since April do I need to play with the air/fuel mix needle ? The spark plug was just the right colour but I am worried that this will now gunk up. Any help as always, much appreciated.

 

[Lakesailor]

It looks as though the carb is held on with a clamp. It may be there is an O-ring under the clamp which has become dislodged or damaged which would cause weak mixture which is the symptom you describe. It may be still some gum in the carb, so a really good clean out is probably a good idea.
The issue with the engine dying when on the tender could be back pressure in the exhaust with the leg being deeper in the water than when on the dinghy.
Spares are pretty hard to find. If you can speak foreign these people seem to be still supplying.
http://www.tomos-aussenborder.de/

 

[VicS]

I'd go with a partly blocked jet in the carb ( subject of course to ruling out an air leak where the carb is fitted)

 

[oldharry]

Dont know the tomos as such, but the old Ailsa Craig 4 - same engine - had a fuel pump mounted at the front of the engine running off crankcase compression IIRC. If that isnt pumping properly (leaking diaphragm or pressure connector pipe from the crankcase,) it produced the same fuel starvation symptoms - if it had not stopped the engine altogether. Not a lot else to go wrong with those carbs as you say, but the fault is almost certainly fuel starvation from your description.

If the O ring in the fuel connector leaks it loses suction and insufficient fuel reaches the carb - same with any fault on the fuel line (leaky primer bulb etc).

 

[Ecosse120]

I'd go with a partly blocked jet in the carb ( subject of course to ruling out an air leak where the carb is fitted)

Thanks guys, it appears that the carb bowl was not fully tightened. I think that was probably fine before I removed it but the fuel line going in was leaking, I then replaced the fuel line but was getting the same symptoms having resolved the first issue. As always on the forum, great advice and another outboard lives to fight another day.