Chummy fuelling problem

[Cluley]

I have recently got my AD type 1929 chummy back on the road after a 5 year restoration. The car runs and drives very well and is generally O.K. at 30 mph but if I use a main road and drive at 40 the engine cuts out or stops after about half a mile. It will then re-start and drive for another few hundred yards before cutting out again. The engine also often stops when I get to a traffic light.
The car has the bronze 22FZ Zenith carburettor and I have fitted a fuel filter between the tank and carb. I also adjusted the fuel level in the bowl of the carb by putting a fibre washer under the needle valve and re-setting the weights. I did this to stop fuel overflowing and now the carb does not leak. I am hoping not to have to remove and clean the tank because I am not sure this is possible with the engine in place. Any ideas Austin 7 experts?

[Howard Wright]

Hi Cluley

Sounds very much like a fuel blockage.  Removing the tank with the engine in place is not a problem.  Just 4 bolts, there is a very recent thread on this subject.

I had just this problem with the RK (identical tank arrangement in the Chummy). A good clean out with drain cleaner (yes Tesco’s best) thoroughly rinse, dry and no problems since.

Cheers

Howard

[williamsderbys]

Check there is petrol in the bowl when you stop !
Some fuel filters seem to slow down the flow .
JW

[Ian McGowan]

Before removing the tank, apply a little science to the problem. Turn off the petrol at the tap, disconnect the fuel pipe from the carb and insert into a 1 pint empty bottle; turn on the fuel tap and time how long it takes to fill the pint bottle. Some of the petrol taps have a very fine mesh filter integral with their construction. I found that one fitted to my 1929 AD chummy was so fine mesh that it reduced the rate of flow below that required to drive at any speed. If it takes more than 5 minutes to fill the pint bottle, flow rate is your problem. It might be a blockage or restriction due to filters. Investigate this  by emptying the tank and removing the tap, check for any blockage at the tap etc.

[Cluley]

Thanks for the replies. I was thinking along the same lines as Ian, so I will definitely try the milk bottle trick first before I venture to remove the tank. The car definitely runs well when it runs and accelerates fine, just breaks down mainly when fuel demand is high. I might then try a different type of filter as modern filters are designed for modern cars with electric fuel pumps rather than gravity.
Roger

[AustinWood]

Is there a vent hole in the petrol filler cap?

[Chris Farris]

I had exactly the same problem a few years ago when I first got my Chummy back on the road after a 30+ year rebuild. I, too, figured that the problem lay in low fuel flow through the stop tap. After opening out the bore of the tap the problem disappeared and never occurred again.

[Rogerchummy]

I had exactly this problem on my 1927 Chummy. I found that the solution was to put a T-junction in the pipe leading from the tank and fit an open-ended vent pipe to this t-junction which allowed vapour to escape from the fuel before it arrived at the carb. Apparently modern fuels give off far more vapour than some years ago and this excess vapour can effectively block the delivery of fuel from the tank to the carb. It immediately cured the problem which has never recurred since. As my vent pipe is transparent plastic, you can see the vapour bubbles as they escape which proves that the diagnosis is correct.

Email me and I can send to a photo of the set-up

[Rory Nicol]

I had a very similar problem with the Briggs and Stratton engine on my lawnmower. Eventually it got to the point that I couldn't  start it at all. I took the walk of shame to a garden machinery repair shop. The guy there identified that the fuel filter I had fitted previously was for a pumped system and that I needed one for a gravity fed system. Apparently the filters for a pumped system provide too much resistance to flow.The filter was duly replaced and for the first time in several years I can cut all the grass in one go.

[bob46320]

I am glad that the vent pipe (Roger Chummy) worked,  but I don't understand how the vapour didn't escape from the vent hole in the cap of the float chamber, allowing liquid fuel to manage the float properly.  I have suffered plenty of vapour lock over here in France when the temperatures are elevated.  The RN has a front tank which roasts when the air temp is in the high 30s Deg C.  Done the usual, check ignition, insulated exhausts, insulated fuel lines, no vertical coils in the fuel line, no in-line filter, 4 blade fan but now find that using the 98 grade of petrol instead of the 95 has improved the situation. The get me home fix was to remove the bonnet and put it on the back seat !
Good luck in solving your problem.
Bob