fuel starvation on the Zenoah 260PUM engine

[Teslaboats]

Has anyone had problems with fuel starvation on the Zenoah 260PUM engine? I read in the engine instruction manual that the fuel tank should not be more than 100mm from the carb (Walbro WT-644). On my FSRV boat the tank is about 350mm from the carb. To get the engine running well I have to have the High speed needle 2¾ turns open, low speed needle ¾ turns open. 2¾ on the H needle is much more than the recommended setting and a lot of the time the boat just stops, to restart it It needs a bit of choke to get the fuel back into the cylinder. There is always fuel in the primer bulb but as this is on the return side of the carb I am not sure if this means anything.

I wanted to try pipe pressure on the tank, but how is this done with the WT-644 carb as it has a fuel return line.

 

[DaveMarles]

On the 644 carb those needle settings are wrong. Start at 1-3/4 L and 1-1/8 to 1- 1/4 H. The L must always be set richer than normal on an FSRV boat or the motor goes lean in the tight corners. There are no problems on an FSRV boat to run with the tank further away than recommended. The nipple on the primer bulb is an overflow not a return. You must have a separate vent in the tank.

Dave

 

[steve speas]

Has anyone had problems with fuel starvation on the Zenoah 260PUM engine? I read in the engine instruction manual that the fuel tank should not be more than 100mm from the carb (Walbro WT-644). On my FSRV boat the tank is about 350mm from the carb. To get the engine running well I have to have the High speed needle 2¾ turns open, low speed needle ¾ turns open. 2¾ on the H needle is much more than the recommended setting and a lot of the time the boat just stops, to restart it It needs a bit of choke to get the fuel back into the cylinder. There is always fuel in the primer bulb but as this is on the return side of the carb I am not sure if this means anything.I wanted to try pipe pressure on the tank, but how is this done with the WT-644 carb as it has a fuel return line.

1.5 hi and 1.5 on the low is what i run on the 644

 

[Krusty 181]

Hi all , the bulb on the 644 is a primer bulb , keep pumping it and you will only pump fuel out the return line ( which normally is about 2 inches of fuel line to nowhere ) , i would suggest 1 1/8 on the high and 1 3/4 on the low , the 644 has a diaphram fuel pump operated by the crankcase pulses , you may need to check that the little tiny port is not blocked , or that the diaphram is not torn

If you are running a solid tank ( like a sullivan ) you will need to have a tank vent ( you may want to run the vent into another small tank ie 2 oz so when you turn it over you dont fill you main tank with water) as eventually the vacumn created as the fuel is sucked out will be greater than the carb can draw

If you are using an IV bag then you only need the one line to the carb as the carb will just suck the bag down till its empty

and you can certainly use more than 100 mm of line

Once the boat stops pull the plug out of it and see what that tells you about mixture if its all filthy black then your way too rich

Hope it helps

Andrew

 

[Teslaboats]

Thanks for your replies, I do in fact have a vent in the petrol tank so it should not be that I am creating a vacuum stopping the fuel reaching the carb, but I do also have the carb overflow going back to the tank, it saves wasting any petrol in the boat or overboard, but I will try just venting the overflow to nowhere to see if there is a difference.

An interesting point you make Dave in that if the L needle is not open enough the boat leans out in a tight turn as this is when it mostly stops, when I turn left the engine slows right down and dies.

For reference:

Plug is a NGK CR8HIX

Oil is Castrol A747 mixed 25:1

Prop Mocom 2432

 

[Krusty 181]

Where abouts in your tank is the pick up? it should be in the back left hand corner of the tank if your racing a right hand circuit , but as you will always have to be able to turn right and left to avoid another boat for example i would suggest you put an IV bag in , i use one with a dubro gasoline filling point in the line , that way once you fill the tank you can hold the bag vertical and suck all the air out of it , then you will only ever get fuel to the engine regardless of the attitude of the boat

Andrew

 

[DaveMarles]

Prop is good, plug is good, but 25:1 is not enough oil. You need at least 16:1 and better 14:1 and always rely on doing a plug chop as Andrew recommends.

 

[Mark McCray]

Two years ago, I had a boat that ran with the best of them and I had to touch up the paint job so I took it all apart and after the paint was done put it back together. Took it back to the pond for some testing and it wouldn't run. I mean it stalled out everytime it got on the back straight away. I just could not figure out why it wouldn't run. My ace was my engine man you so kindly broke down the engiine 3 times in search of the problem. An after rebuilding the engine and then putting a brand new one in and it still wouldn't run. For the shits and grins, I pulled the IV bag out of the boat and taped it to the outside of the hull and the dam boat ran like the wind. The answer, I come to find out it all had to do with the oreintation of the tank, had nothing to do with the engine, the length of the fuel line, just everything to do with the way the IV bag sat.

Just my ten sence worth.

Mark