Fuel Delivery Problem

[al40]

My 2006 Tohatsu 50 seems to have a fuel delivery problem. It runs fine but if it's run at WOT for more than a minute or so it dies. It can be run sustained at 4300RPM or under.

I originally saw this issue on my old boat (transferred engine from old to new) where I had a water seperator and possibility to connect 2 tanks. It seemed OK when both tanks were connected (ie could run at WOT for sustained period) but gave problems with just 1 tank connected.

On new boat, it's an underfloor tank with a water seperating filter and new hose / primer bulb etc. The filter is the factor fit Ribcraft one which is supposedly suitable for engines to 100HP - haven't looked at flow rate). The fuel pipe is inside a plastic conduit which in turn is inside the cable duct under the floor so it should not have got crushed. Fuel hose is interal diameter of approx 6mm (may be slightly bigger).

I have yet to connect up a std tank direct to the engine (will do that this weekend weather permitting) and would also like to check if the primer bulb goes flat when the engine stalls but:

- Does anyone know if the Tohatsu 50 has a weak fuel pump of any description? The fact that it's been a problem on 2 boats points me more to the engine side rather than fuel side. It may just not be able to cope with extra resitance from an inline filter. I guess an underfloor tank will also make the fuel a little harder to pump.

Any other thoughts?

[Pete7]

Best guess, I would have a very good look at the fuel pump for possible leak or hair line crack in the pump body. If its like the the Merc ones there will be 3 rubber diaphrams inside. A pin hole in any will cause problems. Leak from from the internal engine filter could also cause this.

Pete

[al40]

Thanks. Hopefully take a look at it this weekend. I'll rig up an Aux tank with short hose and no in-line filter and see if the problem persists. Either way I'll also investigate the pump and filter. I would hope the pump is OK as engine is just over a year old!

[jyasaki]

Sounds like you've got a pretty good line on what to do.

FWIW, if it is the fuel pump, the primer ball should not be going flat. A flat ball would indicate some restriction between the ball and the fuel in the tank (i.e. the motor is sucking more than the fuel line can supply, and the resulting suction collapses the ball.) Poor pumping would not create a vacuum in the line, so ball should stay up.

You can usually verify that it's a fuel delivery problem by manually pumping the primer ball while running (won't work with a collapsed ball, though.)

Good luck;

jky

[yoyo]

Hi Al40,
Dont all Tohatsu motors carry a standard 2 year warranty? Can you speak to your supplier about your problem?

It will be interesting to see if the problem is still there when you run the test with the standard tank and short fuel line.

I ran a 50 Tohatsu with fuel fed from from two tanks in the bow for a couple of years and had no such propblems. It does sound like a leaking diaphram on the fuel pump.

[al40]

Originally Posted by yoyo

Hi Al40,
Dont all Tohatsu motors carry a standard 2 year warranty? Can you speak to your supplier about your problem?

It will be interesting to see if the problem is still there when you run the test with the standard tank and short fuel line.

I ran a 50 Tohatsu with fuel fed from from two tanks in the bow for a couple of years and had no such propblems. It does sound like a leaking diaphram on the fuel pump.

Hi, Yes they have a 2 yr warranty but with the usual exclusion of it having to be done at a tohatsu service agent. Unfortunately they are quite sparse in Scotland... I'll have a try with the remote tank and see if that helps narrow it down. Pumping the bulb is also a good call.

Once I've run it from the remote tank I'll post the results.

Thanks

[jwalker]

One more thing for you to check, if the engine has a removable fuel line connector, very carefully check the condition of the sealing O-ring. A small score or nick will allow air to be drawn past when the pump is working hard and really starts to suck. Personal experience.

[jyasaki]

The fuel line itself can rot and develop holes, too. Usually shows up when you prime the bulb with a bit of vigor.

jky

[al40]

I did check the fuel hoses and they all appeared OK and I can pump the bulb pretty hard with no apparent leaks - but I'll certainly double check the o-ring on the connector if it ever stops raining and I can get to the boat!

[AndrewH]

You didn't get your fuel from Tescos or Morrison did you?