Tohatsu 2 stroke 50hp cuts out at high revs

pabeer · 19 July 2015, 10:20

Hi, I have recently purchased a RIB and I am new to boating!
I changed the spark plug(3) on the outboard a couple of months ago and checked the fuel and oil filters. Since them the engine cuts out at high revs. I starts back up immediately and runs fine on half revs, I am thinking that fuel isnt getting through but I am not sure what to check, any help greatly appreciated.

paintman · 19 July 2015, 10:47

Stating the obvious, but start at the fuel tank - pickup pipe, vent - & work your way all the way through.
Is the fuel filter blocked?
If it didn't do this before you worked on it then the first thought is that something you've done/replaced is the problem.

pabeer · 19 July 2015, 11:35

Thanks Paintman, my boat is down in Portugal and I will be going down at the end of July so I will check then. I had a couple of people 'helping' me when I was working on it and it could be that something was put back incorrectly. I will check the fuel filters first!

spartacus · 19 July 2015, 12:02

Is it definitely the right sparkplugs? Tohatsu 50hp model D2 uses NGK-BH8S-10 or BR8S-10 gapped at 1.0mm. Ensure the HT leads sit tight on the plugs. Sometimes you can crimp the connection if it's a little suspect.

Definitely rule out fuel as suggested. The male fuel connector can fail. The push-pull release is prone to corrosion, so lube lightly after cleaning with steel wool. Also check the 'o'-ring and ball-bearring inside hasn't been dislodged.

When did you last replace the primer bulb? The fuel bulb internals can collapse, so if it feels particularly hard or is difficult to prime, then replace. Genuine Tohatsu or Quicksilver only.

Drain the carbs using the large slot hex nut on each carb bowl. Any contamination, then strip the carbs down and clean. Don't adjust pilot screws, etc.

Finally, the fuel pump. With the engine running, you can detach slightly from the engine. The engine produces a vacuum which draws fuel. You can test by pressing the fuel bulb to see fuel flowing out. if it's suspect, then opt for a new diaphragm kit and rebuild. New fuel pumps are daft money.

Because the boat is abroad, I'd order a new fuel-pump kit, primer bulb, fuel hose connector and spark-plugs. All useful spares anyway. You don't want your trip ruined because you're waiting on parts. Not sure what dealer network is like in Portugal. When I was there last it seemed like shiny Yamaha 4-strokes all the way.

pabeer · 19 July 2015, 12:52

Hi Spartacus, Thanks very much for all that information, its very much appreciated. Could you recommend and online store where I could order the items you mentioned?

spartacus · 19 July 2015, 13:01

I order from Gaelforce (Inverness), ask for Nik. Call and he'll locate part numbers, etc. Tohatsu UK have £5 shipping charge even if it's a single rubber grommet so it makes sense to order a few things at the same time. Gaelforce then forward onto you, plus VAT and postage.

Chandlery, Sailing Clothing & Boat Electronics | Gael Force Marine

Nightfisher · 26 July 2015, 07:56

Hi, Plug Gap wrong; High tension wires leaking; Coil is where I'd start looking. You may also check each plug for fowling indicating misfiring which would most certainly point toward one or more of the above. Good luck.

pabeer · 01 August 2015, 07:42

Thanks Nightfisher, I am in Portugal now and will check all suggestions. I suspect that it could be the spark plug gap as the problem only started after I changed the plugs and I didn't check the gap before I put them in!

paintman · 01 August 2015, 10:25

If it doesn't solve it & you still have the old plugs be worth putting them back in to check.

pabeer · 03 August 2015, 07:58

Plug gaps and cleaning fuel tank breather seems to have fixed the problem, thanks to everyone for their help. Problem now is an intermittent engine alarm with no associated oil light! I took the oil filter off and I think air got in then, anyone know of an easy way to purge the oil lines? Thanks again guys!