Fuel issue

#1
I recently finished some recommissioning of a 1974 V8 manual. On it’s first test run, it broke down, there was no fuel in the filter. I managed to crank it and get it running and limped home. On the next run it misfired but didn’t break down. I left the car in the garage for a month or two until today. I had idling on the drive and after 10 minutes or so it cut out, again, no fuel in the filter. After much cranking it refused to fire so I checked that fuel was getting to the O/s carb by disconnecting the union. There was very little fuel there so I cranked the engine with the union off (it had cooled by then) and a fair splash of fuel emerged and the engine started with the union off! I switched off, reconnected and it ran very happily so I put it back in the garage. What do you think the problem is? Is it an air lock, worn pump, blocked pipes etc? It’s on standard carbs and manual fuel pump.
 
#2
I had similar issues trying to sort mine out in 2016, in the end it was a combination of things, what we finished up doing was:-
changed oil
changed electric fuel pump
changed coil
added electronic ignition
new plugs and leads
set timing

and truth be told, it’s not been touched (much) since, runs like a dream, been out this afternoon, her 45th birthday!
 
#3
I recently finished some recommissioning of a 1974 V8 manual. On it’s first test run, it broke down, there was no fuel in the filter. I managed to crank it and get it running and limped home. On the next run it misfired but didn’t break down. I left the car in the garage for a month or two until today. I had idling on the drive and after 10 minutes or so it cut out, again, no fuel in the filter. After much cranking it refused to fire so I checked that fuel was getting to the O/s carb by disconnecting the union. There was very little fuel there so I cranked the engine with the union off (it had cooled by then) and a fair splash of fuel emerged and the engine started with the union off! I switched off, reconnected and it ran very happily so I put it back in the garage. What do you think the problem is? Is it an air lock, worn pump, blocked pipes etc? It’s on standard carbs and manual fuel pump.
I'm going to go with a combination of things giving you grief.
Sludge/gunk/stuff in the tank is collecting around the pick-up pipe and slowing flow.
Said stuff is then hitting the filter and further clogging the works.
Slowed fuel flow is allowing for reduced pressure in fuel lines and this is accelerating the vapourisation in the lines causing airlock.

Solutions...
Remove the sender unit in the tank and clean out as much as you can OR remove the tank and do same if you have the knowledge/inclination.
Remove the line at engine end and blow it clear to free debris.
Replace filter
Probably need to service/replace pump sometime soon, too. may as well do it now.
 

SydneyRoverP6B

Well-Known Member
Staff member
#4
Hello Badrover,
I second John's view that it sounds very much like a blockage in your fuel line, between the tank and the fuel pump, or indeed within the tank itself, blocking the fuel outlet.

Slowed fuel flow is allowing for reduced pressure in fuel lines and this is accelerating the vapourisation in the lines causing airlock.
Hello John,

Sorry, but I am going to disagree with you on this point. I know it sounds intuitive that if the velocity of a fluid decreases, then the pressure will also decrease, but that is not strictly true. Radial pressure (the pressure exerted by the fuel against the inside circumferential surface of the pipe) will increase when the fuel velocity decreases and vice versa. This is all down to the Conservation of Energy and the First Law of Thermodynamics which says in brief terms that energy is always conserved for an isolated system. Incompressible fluids that are also inviscid are linked through Bernoulli's equation (which is derived from Newton's second law) and whilst fuel is in essence neither incompressible nor inviscid, we can accept the application here.

Ron.
 
#5
Many thanks for your responses. You’ve confirmed my suspicions to be honest. I’m keen to make it a reliable car to use so I’ll remove the sender and clear any detritus and have a good look/feel around in the tank. If it’s full of crud then I’ll take the tank out and do a proper clean. Then disconnect the pipes and blow them through with the airline before a New seal kit for the pump and new filter. Fingers crossed and thanks again.
 
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