Carb problem

[Ron Pier]

I have managed to diagnose a non starting issue to my MK2 to be that the float bowl is not filling. The float bowl shut off valve seems to stick up and the pressure from my modern electric pump is not sufficient to free it.
(The pump has worked fine up to the problem this weekend)

I've taken the top off and cleaned everything up and lapped in the valve, but still it has a tendency to stick up when operated off the vehicle and blowing through the fuel pipe by mouth doesn't free it.....Then it drops on it own or with a small tap.

So I went to Royal Kustoms and bought a new valve and found it's giving exactly the same problem. I can actually free it if I blow hard enough. I just don't understand why it sticks? I would think it should fall freely under it's own weight.

Any tips or advice regarding the pumps etc.
Cheers Ron

PS Carb is a Ford 94

[rob love]

I had that problem here and blame ethanol fuel. There are companies who sell the needle valves with an ethanol resistant tip, which cured the vehicles here of the problem.

You can also give the carb a rap with a screwdriver handle before trying to start, but that gets a little tiring after a while.

[Paul Singleton]

Yes I have had this problem. The needle is tapered but the seat should be a square cut edge. When the needle closes it should seat against the square edge so that there is a small contact area against the needle. This very fine line of contact is easily overcome by fuel pump pressure. When the seat area wears it wears in a taper to match the needle. What happens is the needle will now lock into the taper worn into the seat similar to a steering tie rod or track rod end. The carburetor manufacturers in later years used a neoprene tip on the needle to stop the seat wearing into a taper. Hope this is helpful.

Paul

[Ron Pier]

Thanks for those replies from Canada chaps. I'm heartened that it's not just me who's had this problem. My new needle has a black tip which is different from the one I removed. I'll assemble the carb today and see if the new valve will work against the pump pressure and report back. Ron

[Lynn Eades]

I bought a modern (improved?) needle valve assembly from a Holley carb parts supplier in the USA. I found him on epay, but do not remember who he is.
It works fine btw. Also Ron if you happen to have a vacuum / pressure gauge, try blowing in it. You probably cant move the needle? Does your float arm have a dimple worn into it? Is the pivot pin worn and floppy? If you suspect the valve is sticking, then you need to start suspecting the parts involved. Electric pumps push better than pull, as a general rule. What is your pump delivery pressure?

If you are trying to start from cold (after a time) then you needle valve is likely open already (because the petrol (or some) in the bowl has evaporated) This would mean that there is no resistance to fuel flow and yet your bowl is dry. This might be because the pump is "dry" and wont prime? Maybe you have an air leak on the suction side of the pump?
That should give you a few things to think about?
Not knowing all the details makes distance diagnosis difficult....

[Ron Pier]

Thanks Lynn. I did previously have a fuel issue that turned out to be one of the things you mentioned. After several days of messing about and rebuilding the original mechanical pump, after which I gave up and fitted the electric pump. It turn out to be a leak in the flexible pick up pipe from the tank. But I'm sure it's not that this time as the pump is delivering fuel ok, but it wasn't getting into the float chamber.

My electric pump was not expensive and I have no pressure gauge, but it's been working brilliantly up to now. What I especially like is that it primes the float chamber without churning the engine over before hand.....There is no hand primer on my unit, even if I wanted to climb in the back and remove an engine cover to do it. Ron

[Lynn Eades]

Hi Ron, I only have electric pumps (no mechanical) I have one for each tank and a change over switch at the diff pinion area.
I am wondering if you are sucking air? Each of those hoses can be leaking at either end, at the flexible connections and at any point in the flex as well as from your change over tap. That's 3 hoses and the tap, on the suction side of your pump (I think?)

[rob love]

https://daytonaparts.com/daytona-car...oat-valve.html


Found this on the net: A new design for the needle valve. I may give this a try this summer if they have parts applicable to the carb I am using.