Fuel Delivery Problem

al40 · 21 February 2007, 20:59

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 · 21 February 2007, 21:41

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 · 22 February 2007, 22:07

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 · 24 February 2007, 19:42

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 · 25 February 2007, 18:29

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 · 27 February 2007, 23:05

Quote:

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 · 28 February 2007, 00:21

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 · 28 February 2007, 03:27

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 · 28 February 2007, 21:20

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 · 28 February 2007, 22:35

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

al40 · 03 March 2007, 23:36

Quote:

Originally Posted by AndrewH

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

Unfotunately not - I'd be quite pleased if this was the cause as at least I'd know what was causing it:-)

Got out in the boat today and confirmed that it ran OK with a small aux tank connected directly to the engine - WOT for 10 mins no probs. With the main tank connected, the engine dies after a minute at WOT.

So, I don't really know if that helps narrow it down. I'll need to go out with someone else (other than the wife who was holding the children) on a calm day to see if the primer bulk is going flat - it's inside the console and would require sitting in the bow to see it - not easy if your driving.

I had a good look at the connector and the o-ring is OK - changing the connector didn't seem to help (I broke the old one a few weeks ago...)

Has anyone had any issues with fuel hose flattening? It's TEMPO fuel hose (internal 3/8 diam) and seems quite soft to me. It's new and the guy I got it from assured me it was the latest spec stuff. I had TEMPO hose on my last RIB but it was braided and seemed a lot more solid. Was wondering if this would be a possible problem. The fuel hose is inside a conduit pretty much all the way from the fuel filter to the engine so it can't get squashed by any other cables, hoses etc.

Hightower · 04 March 2007, 01:07

Ditch the Tempo fuel line or rather the primer bulbs. Their Bulbs are crap, I think the one way valves are stiff and restrict the amount of fuel getting though hence your fuel starvation. Buy a decent one. Quicksilver do some that are good.

al40 · 04 March 2007, 23:17

Quote:

Originally Posted by Hightower

Ditch the Tempo fuel line or rather the primer bulbs. Their Bulbs are crap, I think the one way valves are stiff and restrict the amount of fuel getting though hence your fuel starvation. Buy a decent one. Quicksilver do some that are good.

Hi Hightower,

I don't think it's a tempo bulb - I bought the tube off a drum and got the bulb seperately but in any case I can certainly check with another bulb (like the one from my original tohatsu fuel line).

Good call - I hadn't thought about that and depending on what valve it is and relative position in the bulb, it may not even show with the bulb flattening!

jyasaki · 07 March 2007, 17:04

I'll reiterate my experience with a replacement Tempo fuel line for my 14' Achilles/40-4 Honda:

Developed a leak at the motor fuel connection, so bought a new Tempo fuel line: Hoses (2), primer bulb, and 2 connectors (one for the fuel tank and one for the motor; both spec'd for my particular application.) Put it all on, and had the following problems:

1) Fuel tank connection would fall off if you looked at it wrong. Replaced with connector off the old fuel line.

2) Motor connection would fall of if touched. Re-shaped the SS locking clip, and filed a larger cutout into it to get a better grip on the locking pin.

3) Primer bulb would pump once, but would stay flat. Initially suspected that the dry-break connectors were never getting past the "dry" part; but in troubleshooting, found that after removing the bulb completely from the line, it operated the same way. The thing wouldn't even pump air. Replaced with the OEM Honda bulb from the old line, and everything worked fine after that.

No more Tempo crap for me.

jky

al40 · 07 March 2007, 18:18

The concesus seems to be Tempo stuff is no good.

What are the suggestions for a good make of fuel hose (and where to get it)? I need approx 5m of just fuel hose, pref braided and a primer bulb. To be honest the fuel hose itself does look OK (seeing as it's just hose), it's quite soft but I can't see it flattening that easily.

Hightower has already suggested a Quicksilver primer bulb. Everywhere I look the Tempo ultraflow seem to be present claiming 35% more flow that others.

Confusing!

jwalker · 07 March 2007, 18:25

Petrol fuel hose by the length from a motor factors. It'll be reinforced too rather than the cheap rubbish which comes with outboards.

jyasaki · 08 March 2007, 16:15

Any chandler will have the marine rated fuel hose (which is most likely the same as your local garage will have, but with a bit more ink on the side.)

As far as the bulb, get the OEM one from a shop that represents your motor (or, in truth, any motor manufacturer - they're not really different brand to brand.)

jky

al40 · 08 March 2007, 20:10

Had an interesting coversation with Tohatsu. Basically they claim that the way the boat is rigged will not allow the engine to suck enough fuel. Fuel filter is mounted in console (like all RC's) with a short length of hose from tank to fuel filter. Then the primer bulb and long run to the engine. The tohatsu engineer claimed that because the fuel filter was just after the tank, that this made it much harder for the engine to suck fuel.

True or False?

I personally suspect that the narrow bore of 5m of hose will provide a higher resitance path than the fuel filter so it doesn't make any diff where the filter is placed. I much prefer it in the console anyway as it's out of the way and doesn't rust.

The next thing the Tohatsu engineer stated was that the cartridge type filters (ie water seperating cartridge filters) we no good and that one with a sight bowl was better.

In speaking with Ribcraft, the default filter is rated for flow rate to at least 100HP (it's a quicksilver one apparently) and they have used them on opti 150's with no problem. I don't know the micron rating of the filter, or flow rate, but I assume it must be relatively high to give adequate flow for 100HP

So 2nd question is, should I be looking to install a bowl type filter or stick with what I've got?

I've decided my next course of action is to prime the engine then effectively remove the primer bulb and fuel filter from the euqation and connect the hose direct to the fuel tap. If that runs then the hose must be OK and the problem lies somewhere in the filter or bulb.

Cheers
Al.

Pete7 · 09 March 2007, 11:15

Quote:

I've decided my next course of action is to prime the engine then effectively remove the primer bulb and fuel filter from the euqation and connect the hose direct to the fuel tap. If that runs then the hose must be OK and the problem lies somewhere in the filter or bulb. Cheers Al.

Good plan, b

yoyo · 10 March 2007, 08:35

here is a pic of the filter/seperator and bulb setup on my Tohatsu 70.