Dexta chasing air in the fuel

dextainwa

Member
For three years, gravity feed through the filter to the injection pump worked well on the Dexta I had bought. A few weeks ago, while working it harder than usual running a 60inch brush mower through my tall grass, it started to act like it was running out of fuel. There was 2 inches of fuel in the tank and when I let it run without a load on it for a minute; it cleared up and ran well. When I started mowing again, after a few minutes it repeated the weak power that seemed to be like it was running out of fuel. I let it idle and it cleared up again, so into the shed until I could work on it.
Now, I've got a new OEM mechanical lift pump mounted and piped through the filter. I replaced the filter too, as it was dirty.
I finally got a chance to go out in the field and do a test run. It started well, ran well and mowed great for about 15 minutes. Then the power dropped off, just as before, it would barely idle, but kept running. This time it did not clear up and run well, instead, it slowly ran worse and worse until it stopped.
My neighbor brought his tractor over and towed it into the yard for for me.
I just got done working on it, and what I found was it was air locked, so bleeding it got it running well again. Thank goodness for the little primer lever on the lift pump.
There is still 2 inches of fuel in the tank; the primer lever on the lift pump tells me the lift pump is holding pressure after I have run the motor and shut it down.
Where did the air come from? My line from the tank to the lift pump does not leak. Could the pump itself be leaking air into the fuel it pumps to the filter? But of course the pump wasn't in the system when it did it the first time.
Any other ideas would be appreciated.
David
 
Hi
I'm going to guess it's nearly running out of
fuel with the 2" in the tank. if that tank is
set up like the major.
The tap has an emergency fuel reserve. to run
normal the taps not right out. for emergency
you undo the tap screw right out until it hits
the stop. this then opens a hole right at the
bottom of the tap to run on the last fuel.

It could be that hole is plugged with junk, if
the taps right out now. and starving the fuel
while it slops as you drive because the fuel
can't run out at the height of the tap inlet
due to lower fuel level.

There should be a strainer on top of the tank
outlet inside this could be plugged also about
an inch up or so up. Have you taken the fuel
line off the tractor to see if you have a good
flow, from the tank.
i really suspect either low fuel or somethings
plugged in the tank with junk. thats a possibly
50 year old tractor. if junks in the filter
it's in the tank.
you need to find out if you got a good flow or
blockage or add fuel you are very close to
running out at this point. maybe you have no
outlet screen and something floats over and
restricts flow to, then moves off when it sits
not running.
Hope some of this makes sense. I do this for a
living but find it hard to explain online when
i can't see whats actually going on with your
tractor and system.
Regards Robert
 

Thanks; I'll start with the flow from the fuel line to the pump, as that will tell me if the tap is flowing well.

Looking in the tank show the little screen has come loose and is rolling around on the bottom of the tank. It is not doing any good there.

I'll report back when I can.
 

Testing fuel flow from the line out of the tank tap showed very low rate. It was less than one ounce in a minute, so not even one gallon per hour.

I'm going to remove and inspect the tap.

David
 

Several projects got moved in front of the Dexta, Finally, the fuel tap was in my hand. Not a simple job the first time as the fuel tank needs to be lifted several inches to allow the fuel tap to be unthreaded.

The inlet of the fuel tap was blocked with many small black objects, some appear to be rubber and some appear to be the remnants of bugs. The tap also had crossed threads where the fuel lines are attached, it is no wonder that it had the slow leak. I did find the threads into the tank are pipe threads, with a match for 1/2 inch NPT; about 7/8" OD with 14 pitch; this is also a close fit to BSP -8. I did clean the fuel tank of the remaining debris.

A new fuel tap with a primer pump and the two outlets is available, but too high a price for me. I decided to use locally sourced parts. I now have a ball valve with an inline transparent housing fuel filter. I can easily see if the tap is on, and if the filter is collecting debris. A field test proved that this lets the tractor show its stuff with no loss of power. Fun to feel and hear it work.

I will come up with plan B to create the primer feed to the manifold. The idea of using an outboard (boat motor) fuel tank primer line seems to have some appeal. I think the USA versions of the Dexta have a check valve in the fitting at the manifold; that would prevent siphoning.

David in Washington state, USA
 

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