Fuel starvation.

[Ray White]

My 1930 Swallow - better known as Trundles - has lately been exhibiting symptoms of fuel starvation.  The gravity tank is clean and the line to the up draught FZB Zenith carb is clear.  I have checked the filter in the bottom of the carb and it is clean as a whistle.  When the problem occurs, the float chamber is empty.  

Is it possible for the needle valve to stick down with the float chamber empty ...thus preventing any petrol from getting through? 

Obviously I shut off the petrol supply at the tank before removing the float chamber lid and float but if I open the tap, petrol gets through.

[Tony Press]

Silly question- breather hole in tank cap ?

[Ray White]

Bot a silly question at all.  I have had that before but not this time.  Besides, the cap is not a tight fit.

I had the car running fine again last night.  It might be O.K. in the garage but I don't want it break down again in the road.

[Howard Wright]

Hi Ray

I’ve had this problem before and it turned out to be a quite large bit of ‘dirt’ in the pipe.  Running it makes its way to the carb and blocks it.  Stop and it floats back up the pipe seemingly allowing fuel to flow freely again.  Take the pipe off and blow through. 

Cheers

Howard

[Ray White]

The first thing I did was take off the pipe and ensure it was clear.  I also took the tank out and removed the tap. I made sure there was nothing blocking the outlet. I know it is always possible for a large flake of sealant to break off and temporarily block the outlet... but I am pretty confident the tank is not the problem.

As I said when I opened the tap the petrol came out O.K

Before anyone asks,,,, yes, there is plenty of petrol in there.

 I think is the valve is closing up somehow.  

If it happens again I will whip the carb off and investigate.

[Robert Foreman]

What condition is the needle in?

[Mike Costigan]

Could be a large piece of dirt (rust flake?) actually inside the tank which floats over the outlet.

[Howard Wright]

Hi Ray

Another possibility is that the bob weights are sticking. Although it’s more likely they would stick open!

Is there any sign of leakage from the carb?

Cheers

Howard

[Ray White]

As I said I checked for flaking inside the tank and found nothing.

The needle does it's job reasonably well but the float chamber lid has to be in the right position or it can leak...but that is the opposite problem.!

The bob weights are worn but I turned them over to take advantage of the unworn side. I can't get them to stick in the closed position.

I wonder if there is an issue with the valve? Quite what it could be I won't know until I examine the carb on the bench. I don't know whether to risk it happening again or not.

[Steve Jones]

Does your fuel tap have a reserve? When I had a similar problem last year, pulling the reserve solved it. Turned out there was a partial blockage in the main tap stand pipe that reduced its diameter but didn't fully stop the flow and the engine was using more fuel than the tap could deliver. Taking the top of the carb off when this happened showed an empty float bowl but turning the fuel on produced a flow.

Steve