NAD and embarrassing non-start

[Mr K]

Good to see everyone at NAD today.

After looking round all the cars I had a look round the house - thought I might as well as it was only £3.50.

Tried to leave, but after briefly catching, the engine refused to start. Turned over fine on the starter. A few people gathered round and diagnosed lack of fuel (benefit of a clear, new fuel filter). Peter suggested a downhill push start, so we tried that and it worked. A big thank-you to those who helped! I then drove 85 miles home without issue. A few hours later I tried to work out what the issue was, expecting to have to buy a new fuel pump.

Diagnosic steps: with pipe off the fuel filter, turned over engine, almost no fuel pumped out.

Removed inlet pipe from pump. Lots of sucking and a noise from the fuel tank as it flexed back into shape.

Took off fuel filler cap, reattached inlet to pump and turned over engine on the starter. Result - lots of fuel pulsing out.

So it's not the pump, it's lack of ventilation to the fuel tank, which is forming a vacuum on a long journey, which the pump struggles to fight. It restarts if left long enough as it gradually releases the vacuum. It still had a vacuum 3 hours after I got home, which explains why I couldn't start it this afternoon. The FIST locking filler cap doesn't have a vent that I can see. Any ideas how the tank should be vented?

Cheers!

[Kegsti66]

Glad to hear you have got home ok. Also good to know you have diagnosed the cause.
I can not remember the venting set up to the tank so hope someone else can help. Is it through the cap on a single carb engine?
Glad it started as Peter and I were out of puff
Good job mine started as there was know one left to push !!

[Mr K]

Glad to give you guys an excuse for some exercise! Thanks Kegsti66.

Just been reading my Haynes manual (post on forum, then RTFM is the correct order). It mentions a blocked tank air vent but doesn't say/show what and where it is. Probably in the original cap, which I replaced with a locking one decades ago. I'll have to see if I can find it.

[Veesix75]

I havnt looked at the manual for a while, but I thought the venting is in the filler neck ?

[Sud 145]

Remember seeing this problem on a Mk3 Cortina - the tank was totally buckled no wonder he could only get 5 galls in it.

[alfadave]

Veesix75 is right
There is a small outlet off the top of filler tube to vent the tank.
You need a length of pipe and a one way valve on the end to let air in, but avoid fumes escaping.
Loads of these on ebay

Dave

[alfadave]

The original green breather pipe runs along the rear of the tank.
Probably best to renew the pipe and one way valve completely if you've been having problems with venting

Dave

[Mr K]

Thanks Alfadave. I've found, removed and tested the original valve. It seemed to be letting air out, but not in, which is odd as it can't be fitted the wrong way round because of the different pipe diameters. I've ordered a valve.

More thoughts. The car was facing uphill at NAD, so the pump had to fight gravity and the partial vacuum. Probably explains a couple of things. Why it hasn't happened before, and why the car seemed to lack power going uphill in Derbyshire last year. I put it down to me being used to more powerful cars, and the weight of the whole family being on board.