Engine MK V problem

#1

Hello.
I have another problem and I turn to you for help.
Last time you helped me a lot and I’m coutning on it now.
My MK V engine work uneven and smokes black out exhaust.
Do you have an idea what might be the reason?

Thank you very much for all the help
Pawel

(Robin O'Connor) #2

Black smoke indicates the engine is running too rich, is the choke turning off completely?

(Rob Reilly) #3

Pawel, in case the answer given by Robin is not clear, he means the starting carburetor which is the small one in between the other two larger carbs. It makes a hissing noise when the valve inside it is open. When the power to the wires shuts off, the valve inside should shut off the air flow in this carb and there should be no hissing.
If the hissing stops and the car still puts out black smoke, the next thing to try is the jet adjustment screws under the main carbs. They have covers over them which must be removed first, then turn the screws upwards one turn and see if there is any improvement.

#4

Thank you for you response.
The choke turning off, so I will try the second option

(Lovell) #5

Did not realize MKV’s had triples?

(Rob Reilly) #6

Two main carbs and a little starting carb in between them.

#7

Hello.
I have two more questions.

  1. Do you think the use of a too thin needle may use cause the above symptoms?
  2. Should the element marked in the picture be in the carburettors? I do not have it.

Thank you

(Robin O'Connor) #8

1 yes a thin needle would allow excess fuel to be drawn into the carburettor.

2 the arrow is pointing to the lifting pin which is used to test if the mixture is correct, lean or rich by how the engine reacts when it is lifted. It should be there, it may affect the mixture slightly if its open to atmosphere? Allowing a small air leak in under the piston?
From memory a lift will raise the idle and then settle back if the mixture is correct.
If the idle raises and stays elevate the mixture is too rich, (jet too low)

If the engine hesitates then the mixture is lean. It dosen’t sound like this is your situation.

(Roger McWilliams) #9

The needle for Mark V main carbs is listed as F.W. in the shop manual.

To the best of my knowledge Mark V carbs did not come with lifting pins. The shop manual pictures and description rely on the screwdriver lift method for checking mixture. Given the interchangeability of carbs, lift pins may be found on some now and are convenient.

Be sure to note the difference in piston lift distances described in various manuals for determining mixture richness. Different piston lift heights give different outcomes. Haynes, SU, and the Jag Mark V shop manuals do not all use the same lift heights.

(Rob Reilly) #10

Shall we mention the possibility of a sunken float…

(Roger McWilliams) #11

Yes, sunken float, float stuck low, and float chamber valve not seating (often due to fuel pressure too high from incorrect fuel pump). All these lead to smoke at idle (and fire hazard) and less smoke at speed.

(Graham Jordan) #12

When / how did it begin? Was it running ok before?
Starting carb is easily disturbed. Check the solenoid hasn’t been bumped and is not sealing. It should be straight up and down. It’s a simple devise if you want to remove the solenoid and check the valve inside is ok.
Eliminate this as being a problem before disturbing your carbs
Then. First and easiest carb check is what Roger mentions.
With the engine warmed up and running at idle use a screwdriver and slightly lift the piston in one carb up one at a time.
Note how the engine responds. If the engine speeds up then that carb is too rich.
It may narrow your problem down to one carb.
If not there is a long list of things to check. Needle position, needle type (usually FW), needle setting, needle centring, float height etc.
Try the first suggestion as a start point.
Regards, Graham

#13

Thank you very much for valuable information