Fuelling issue - air lock?

[MarkRSi]

Posting on behalf of my old man, from this thread http://www.pistonheads.com/xforums/topic.asp?h=0&a...

I have a '55 Morris Minor (803cc A-Series) and suspect I have a similar "airlock" problem.
The car starts without any difficulty but if I go over 30mph and up even the slightest incline the engine starts to splutter as though it is running out of fuel. If I reduce the speed to 25mph then the engine is smooth again.
Any suggestions would be appreciated.

[stevieturbo]

Hook up a fuel pressure gauge between the pump and the carb/carbs. As close to the carb inlet as possible.

This will let you know if there is a fuel supply issue, at least up until that point

[MarkRSi]

stevieturbo said:

Hook up a fuel pressure gauge between the pump and the carb/carbs. As close to the carb inlet as possible.

This will let you know if there is a fuel supply issue, at least up until that point

Not sure if he's got one or not but will pass it on, cheers

[annodomini2]

Carb probably wants a clean.

[MarkRSi]

annodomini2 said:

Carb probably wants a clean.

I think he's already tried that, although I think the carbs came with the engine which as been sitting around for a decade or two. I'll check if he's got another set of carbs. Or twin Webers (I wish )

[Old Merc]

The fact that it starts OK and runs at low speed indicates that the carb` and lift pump are working OK.There is no fuel line pressure as such with lift pumps and carbs so fitting a pressure gauge will not achieve anything.Your description points to fuel starvation,I suspect a blockage in the fuel line or in the tank.There is enough fuel getting through to keep the carb`float chamber topped up but when you "floor it" it can't keep up.
Remember its almost 60 years old.I expect the tank is full of crap?? the rubber fuel pipes could be perished or collapsed inside?? That sort of thing.
I had this sort of problem and rigged up a pipe from the lift pump into a gallon can of fuel.(be very careful with petrol)Went for a run,problem gone. I then removed the tank and discovered it to be full of crap.

[MarkRSi]

MarkRSi said:

Posting on behalf of my old man, from this thread http://www.pistonheads.com/xforums/topic.asp?h=0&a...

I have a '55 Morris Minor (803cc A-Series) and suspect I have a similar "airlock" problem.
The car starts without any difficulty but if I go over 30mph and up even the slightest incline the engine starts to splutter as though it is running out of fuel. If I reduce the speed to 25mph then the engine is smooth again.
Any suggestions would be appreciated.

Fuel lines to tank appear clear. There is also a good steady flow of fuel if the fuel line to the carb is disconnected and fed into a fuel can.
The carb is the one my old engine used to run with until it was removed a month ago for a rebore. No problems at all with the old engine.
I am starting to suspect the fuel pump diaphragm and will see if any of the club guys have a spare pump or at least a pressure gauge.
Keep the suggestions coming

[stevieturbo]

Old Merc said:

The fact that it starts OK and runs at low speed indicates that the carb` and lift pump are working OK.There is no fuel line pressure as such with lift pumps and carbs so fitting a pressure gauge will not achieve anything.Your description points to fuel starvation,I suspect a blockage in the fuel line or in the tank.There is enough fuel getting through to keep the carb`float chamber topped up but when you "floor it" it can't keep up.
Remember its almost 60 years old.I expect the tank is full of crap?? the rubber fuel pipes could be perished or collapsed inside?? That sort of thing.
I had this sort of problem and rigged up a pipe from the lift pump into a gallon can of fuel.(be very careful with petrol)Went for a run,problem gone. I then removed the tank and discovered it to be full of crap.

If there is no pressure....no fuel would be flowing. Flow requires a differential of some sort. It may be low pressures involved, but still measurable.
Even lowly carb pump setups run 2-3psi fuel supply to the carb.

[phumy]

I take it that it uses an SU carb, if so check the dash pot "lifts" as its should and is free to move on its own, check the oil in the dash pot is the correct spec (3 in 1 oil) is a good starting point and filled to the correct level. If the problem still persists I would be inclined to strip the carb completely and check everything is tight and correct and all gaskets are in place as they should be with no blockages anywhere.

Failing that if it still has the problem, beg steal or borrow another carb and try with that.

[annodomini2]

Has it got the correct needle/jet in it for the engine?

Over fueling will also cause these symptoms.

What colour are the plugs?