Fuel starvation?

[NoviceM]

1970 traveller.
Runs well except.....when accelerating in 3rd gear, it is as if it is not getting enough fuel, coughs and hesitates until I change up to 4th.
Recently, it has started to exhibit similar 'starvation' issues randomly when idling, pulling choke out prevents it from stalling but runs very rough. When this happened this morning, I removed air filter....then seemed fine. Clearly this was a red herring, because I am now running without air filter, but still hesitates accelerating in 3rd.
Just about to change fuel pump
Any other suggestions as to why I might be getting these symptoms. Any suggestions great fully received

[simmitc]

Check that the piston in the carb moves freely - without the damper, if lifted fully and released, it should drop with a nice "clonk". Check oil in damper. Check needle not bent. Check float and valve operating correctly.

Is vacuum, advance in dizzy OK?

Fuel pump flow test, should deliver at least a pint every minute - careful when testing.

[NoviceM]

Many thanks I will work through the useful suggestions. Cheers

[NoviceM]

Oil in damper and needle holder ? drops with happy clunk.
I will measure fuel delivery when I get from work.
Cheers

[svenedin]

Agree to check fuel system. Remove spark plugs and examine colour to get an idea of the fuel mixture.

1) Fuel flow test from pump as already suggested
2) Remove float chamber lid (have a new gasket to hand just in case). Look for rubbish in the bottom of the float chamber, check the fuel level, check the operation of the float needle valve
3) Check fuel mixture
4) Look for holes or cracks in the breather hoses. A leak will draw in air causing the mixture to run very lean. Replace as necessary. Check jubilee clips are secure.

Do you have a PCV valve? Where does the breather from the tappet chest oil separator go to? The later cars use either a PCV valve or a breather hose to a breather version of the HS2 carburettor. This is quite a significant vacuum and any leaks will draw in air making the fuel mixture so weak that the engine will either run extremely rough or not at all. The leaks can be in the hose (cracks that may only be apparent when the hose is flexed), loose clips, perished tappet chest gasket. Of course, though your car is 1970 it may have an earlier engine or the breathing system may have been changed. Spark plugs may show signs of a weak mixture e.g whitish tips.

Stephen

[NoviceM]

1. Fuel flow tested and ok
2. Carb float chamber clean
3. Fuel mixture seems OK by checking plugs...might be a little lean
4. No leaks apparent.
Doesn't have a pcv, tube from the fixed metal canister attached to valve chamber cover, goes from that canister to a port on side of carb.

Still hesitates when revving in 2nd or 3rd . Revs ok out of gear, hesitation seems to be only when e gone is under load, eg climbing a slight hill etc.

In desperation even changed coil in case problem might be electrical.

Sucking on vacuum tube from dizy seems to work, dizy base plate moves very slightly.

I am clutching at straws now.

[svenedin]

Good, you've worked through things.

Have you checked there is oil in the carburettor dashpot? You can use engine oil if you have nothing else.

Also check for any leaks at the manifold and gasket.

Stephen

[Bill_qaz]

Have you checked you are getting full throttle, it can rev out at part throttle with no load but not when under load.
Also is tank breather clear, try with fuel cap loose

[simmitc]

It may sound unlikely, but change the air filter for a new one. Better still, if available, swap it with one that is in another Minor that is working perfectly - see if the fault moves between cars.

[NoviceM]

Running with airfilter temporarily removed.
Petrol filler cap is loose (certainly not air tight)
Oil in dash pot
I will check full throttle travel tomorrow.