60 replies to this topic

[sonscar]

To my uneducated eye I would say that the motor is not healthy.The best plug is too rich and the rest seem to become wetter,maybe even oily.I would be thinking worn rings and or bores.Is the choke holding the jet out at all?,Steve..

[Marc13]

Thanks. You say could be oily...i did massively over fill the dash pot...on a few occasions (not understanding how it worked) - then changed the plugs straight after this. Could this be where the plugs have picked up oil?

[Marc13]

Sorry - a further question. How would I check if the choke is holding the jet out?

[Ethel]

They look about the right colour where it really matters. You really need to be checking after a decent run to get it up to operating temperature so they can burn off fouling. Pulling a choke cable doesn't have the finesse of fuel injection with multiple sensors to  fine tune the fuelling, but there's a "stopped clock" logic achievable for at least one point in the engine tune.

 

 

Did we establish it's a HIF carb? If it is the choke has a separate "jet" that isn't adjustable beyond pulling the choke cable. The quotes are because it's just a drilling in the body of the carb about an inch towards the engine from the main jet. The choke itself is just a spindle valve, not that different to a tap. They do have rubber O ring seals that can fail and the purpose of the separate jet is so it only flows extra fuel  when the throttle is close to closed it's not noticeable when you put your foot down. An indicator they may have failed is not needing to pull the choke beyond fast idle when you probably should.

[Marc13]

Hi Ethel and thanks.
It is a Hiff 44 SU carb.

The 4 photos were taken after a 30 to 40 min run...so a decent enough run I would have thought.

I was mainly puzzled by the fact they get progressively darker and more sooty/(possibly) oily. The 1st two being pretty decent, but then the 3rd and 4th (the two on the left as you look in the engine bay) being a lot darker.

Can you just explain a bit more on....
An indicator they may have failed is not needing to pull the choke beyond fast idle when you probably should. And what (and where) may have failed?

[KTS]

.

I was mainly puzzled by the fact they get progressively darker and more sooty/(possibly) oily. The 1st two being pretty decent, but then the 3rd and 4th (the two on the left as you look in the engine bay) being a lot darker.

worth doing a compression test to see if that shows up anything

[Marc13]

Ok - so how do i do a compression test and what equipment do i need?

[KTS]

You'll need a compression tester. Something like...

https://www.zoro.co....er/p/ZT1120390X

Make sure your battery is fully charged

Take all the plugs out.

For each cylinder in turn, connect the compression tester to where the spark plug would fit and crank the engine over with the throttle fully open, for 5-10seconds. Read and make a note of the pressure shown on the gauge.

When all 4 cylinders have been tested, compare the readings

[Ethel]

Allow time for the battery to recover & motor to cool. It's not a bad idea to also repeat the tests in the reverse order to reduce such errors.

 

Wet soot can look oily.

 

 

....and a plug looking different - it has to stop somewhere one cylinder will have just fired, another will be full of unburned fuel......

[Ethel]

If you can't lay your hands on a compression tester easily, you could spend the time investigating the carb.

 

Did you get the dashpot off?

 

Was there any sign of of all that excess oil?

 

Identify the float chamber breather: the hose that isn't from the fuel pump or the 10mm bore one connected to the engine breathers.

 

If you blow down that, in to the carb, fuel should emerge from the jet (dashpot & piston out). Look at the bottom of the ramp to the engine side & you'll see a small hole, that is the choke jet. You can repeat your blow test with the choke in & out. Stick a finger over the main jet to block it - obvs fuel should not emerge from the choke jet is the choke is closed.

[Marc13]

Is the float chamber breather the one one that is upper left on the side of the car ?

[Marc13]

Carb sorry, not car!

[Ethel]

Probably, there are different flavours of Hif. Most that make it on to an A Series tend to have the hoses on the left, looking from over the engine when fitted in a mini, and cables on the right. There's the outline of internal communication ports visible on the side - a horizontal coming from the air filter/elbow face that drops vertically in to the float chamber. The breather comes is on that right angled corner and is at an upward pointing 45 degree angle. Not to be confused with the bigger pipe by the throttle for the crankcase breather connection.

[Marc13]

photo below - i believe you are saying the float chamber breather is the one to the left of the two just below the dash pot. Its got a hose on it, that just drops to somewhere out the way in the engine bay.

is that correct?

[Ethel]

That's the one