carburettor overflowing

[David.H]

The (FZB) carburettor on my 1929 RK saloon (engine M101897) insists on overflowing. When I got the car it had 2 fibre washers (each ~ 1mm thick) under the needle valve seat. I put the overflowing down to worn needle/seat and as the weights were quite worn I reversed them so that the unworn part was against the float and lapped in the needle/seat. this reduced the overflow to an occasional event. The float does not leak.
At the Beaulieu day I lashed out £24 on a new (sharp) needle and new unworn seat. Replaced everything "as was" (including 2 washers) and once again fuel again poured out of the choke/air intake and squirted out of the carb top vent hole and the needle did not shut off the flow. I removed one fibre washer...no difference.
The car starts easily, runs well and there is no sign of any overflow when the engine is running - even ticking over-. I have had the new seat out & it is clear. If you balance the needle in it and blow, it seals beautifully. Pushing down on the needle does not  shut off the fuel when it is on the car. The needle does seem a bit "sticky" ....there  is no real feeling of the weights being pushed up by the float, but as I say- the float is not losing air & there is no fuel sloshing about in it!
What is the next step? It is doing nothing for the fuel consumption, not the tarmac and is a significant fire hazard (What induced Edge to put the carburettor directly over the exhaust pipe.....?)
David Harrison

[Steve Jones]

The (FZB) carburettor on my 1929 RK saloon (engine M101897) insists on overflowing. When I got the car it had 2 fibre washers (each ~ 1mm thick) under the needle valve seat. I put the overflowing down to worn needle/seat and as the weights were quite worn I reversed them so that the unworn part was against the float and lapped in the needle/seat. this reduced the overflow to an occasional event. The float does not leak.
At the Beaulieu day I lashed out £24 on a new (sharp) needle and new unworn seat. Replaced everything "as was" (including 2 washers) and once again fuel again poured out of the choke/air intake and squirted out of the carb top vent hole and the needle did not shut off the flow. I removed one fibre washer...no difference.
The car starts easily, runs well and there is no sign of any overflow when the engine is running - even ticking over-. I have had the new seat out & it is clear. If you balance the needle in it and blow, it seals beautifully. Pushing down on the needle does not  shut off the fuel when it is on the car. The needle does seem a bit "sticky" ....there  is no real feeling of the weights being pushed up by the float, but as I say- the float is not losing air & there is no fuel sloshing about in it!
What is the next step? It is doing nothing for the fuel consumption, not the tarmac and is a significant fire hazard (What induced Edge to put the carburettor directly over the exhaust pipe.....?)
David Harrison

The obvious answer is that the level of the fuel in the float chamber is too high. Try following Zenith's own advice in their maintenance booklet for this situation and move the collar on the needle '....a shade further from the point'. They say you should unsolder the collar first. I think you might find that the collar isn't soldered to the needle on a repro needle it just being an interference fit. 

Steve

[David.H]

The (FZB) carburettor on my 1929 RK saloon (engine M101897) insists on overflowing. When I got the car it had 2 fibre washers (each ~ 1mm thick) under the needle valve seat. I put the overflowing down to worn needle/seat and as the weights were quite worn I reversed them so that the unworn part was against the float and lapped in the needle/seat. this reduced the overflow to an occasional event. The float does not leak.
At the Beaulieu day I lashed out £24 on a new (sharp) needle and new unworn seat. Replaced everything "as was" (including 2 washers) and once again fuel again poured out of the choke/air intake and squirted out of the carb top vent hole and the needle did not shut off the flow. I removed one fibre washer...no difference.
The car starts easily, runs well and there is no sign of any overflow when the engine is running - even ticking over-. I have had the new seat out & it is clear. If you balance the needle in it and blow, it seals beautifully. Pushing down on the needle does not  shut off the fuel when it is on the car. The needle does seem a bit "sticky" ....there  is no real feeling of the weights being pushed up by the float, but as I say- the float is not losing air & there is no fuel sloshing about in it!
What is the next step? It is doing nothing for the fuel consumption, not the tarmac and is a significant fire hazard (What induced Edge to put the carburettor directly over the exhaust pipe.....?)
David Harrison

The obvious answer is that the level of the fuel in the float chamber is too high. Try following Zenith's own advice in their maintenance booklet for this situation and move the collar on the needle '....a shade further from the point'. They say you should unsolder the collar first. I think you might find that the collar isn't soldered to the needle on a repro needle it just being an interference fit. 

Steve

Thank you Steve. I had read that instruction & shuddered, my soldering skills are minimal, so I hope it is an interference fit! I imagine that the idea of using more washers under the seat was to achieve a similar aim. how many should there be & how thick!? I love the accuracy of that  instruction...."a bit" ...& if doesn't work unsolder it! & try again!
I will first of all compare the collar length with my original blunt needle. Then try & move the collar without putting a flat on the point....it will go away from the point (which is good) without having to touch the point, but if "a bit" is "too much".....getting it back may be interesting!
David

[Ruairidh Dunford]

David,

even when using new, I always lap the needle into the seat with a tiny amount of fine grinding paste.

Once you are happy the collar is correctly placed, I would also give it a little lap.

[David.H]

David,

even when using new, I always lap the needle into the seat with a tiny amount of fine grinding paste.  

Once you are happy the collar is correctly placed, I would also give it a little lap.

Thanks...I have that technology! An ancient pot of fine one end, coarse the other grinding paste. I had not thought about the collar, of course that could be a bit sharp & sticky....but why was this nor the case when the original Zenith parts were new I hear myself ask ??
Back to the washers....how thick should it be & would changing that thickness have a similar effect to moving the collar?
D

[Dave Mann]

With the carburettor on the outside bench I connect up an old lawn mower petrol tank to it for checking the fuel level with the main jet removed so I can actually see the fuel level. I find that T cut does a good job of seating the needle into the seat.

[David.H]

With the carburettor on the outside bench I connect up an old lawn mower petrol tank to it for checking the fuel level with the main jet removed so I can actually see the fuel level.  I find that T cut does a good job of seating the needle into the seat.

That may have to be the next step. I have tried raising the seat by additional washers & that didn't help much, nor did going back to a single washer. What I find strange is that as long as the car is running -  even at a slow tick over, the carb doesn't leak at all! The needle is soldered ( I think I got it from Willie at Beaulieu, with the seat) and I have lapped it in a touch, also where the weights meet the collar. It all spins nicely!".
The only thing I notice is that the one of the bob weights (which I have inverted so that the unworn side is presented to the float) when the needle is in it's uppermost position, hangs down about 1/16" and is "loose" in the groove of the needle. Maybe I need new bob weights...there is no wear on the spindles nor the holes in the bob, so I cannot see why one has this extra vertical movement!
Sod's law, I cannot find the old needle & seat.....but anyway the reason I bought new was that the old one leaked AND THAT STARTED THE WHOLE SAGA!
Meanwhile I keep the extinguisher handy.

[Dave Mann]

I've never tried fitting extra fibre washers under the seat, I've always moved the collar, however if you haven't got the original weight brass split pins and are using ordinary split pins make sure the tails aren't too long, they can stop the float from going up. To reseat a needle and valve I hold the needle in a pedestal drill and with it on its slowest speed add some T cut to the needle and present the seat to the needle. I use very little pressure and keep lowering the seat away from the needle, too much pressure or allowing it to run dry will mess it up.

[David.H]

I've never tried fitting extra fibre washers under the seat, I've always moved the collar, however if you haven't got the original weight brass split pins and are using ordinary split pins make sure the tails aren't too long, they can stop the float from going up. To reseat a needle and valve I hold the needle in a pedestal drill and with it on its slowest speed add some T cut to the needle and present the seat to the needle. I use very little pressure and keep lowering the seat away from the needle, too much pressure or allowing it to run dry will mess it up.

Dave. My bob weights are brass with brass pivot pins that have a small head & a tiny hole the other end to pass a lock wire through, very neat & nicely made. I think that the float may be the root of it all.... if the bowl is full of fuel & the top is off then it floats with almost no freeboard! ie the top is almost level with the fuel level. consulting Mr Nicholson this is not correct, if his sectioned drawing is to be believed. My copy falls open at Page 38 "the carburettor", so maybe it is not an unknown problem. I will take the carb off & see where the level is relative to the jet. Fluid will find it's level! My bodge of raising the valve did not make it easier for the needle to seat and the   needle did not "feel" right! Nicholson tells you how to move the collar on the needle...his method suggests it was an interference fit. I cannot imagine that the collar is wrong on the new pin, so  the float is Suspect No1.
My Hong Kong Californian AG (?) project has arrived this evening, so this problem may take a bit of a back seat while I see what I have got!
Thanks for your help
David