Morris Minor Owners Club

Does anyone know what the mixture setting should be on a Morris 1000? ie. how many turns out from fully tightened. I have blown through the hole under the float that goes to this with a straw ( as I didn't wanna take it apart ) and it seems fine and not blocked, Or should I have taken it off instead?

My Dutch friend always starts of with 12 flats from fully tightened, and then works from there.

It worked on my carb

Onne wrote:My Dutch friend always starts of with 12 flats from fully tightened, and then works from there.

It worked on my carb

12 flats?
I take it you mean 12 full turns, yes?

no, 2 full turns, which equals 12 flats

So what's a flat then? 1/6th I take it?
Is this what the factory setting should be though?

Nuts and bolts have a hexagonal head, ie. they have six flat sides.

There is no "factory setting" that's guaranteed to be correct. To set it correctly you first have to get it close enough that the engine will run smoothly, then you need to fine-tune it. There are several different ways to do the fine-tuning. The way I do it is as described in the manual:

1. Run the engine until it's warm.
2. Make sure the choke is fully off.
3. Screw in the idle speed adjuster screw to increase the idle speed to about 1000RPM (from the usual 600-700).
4. Push the lifter pin on the bottom of the carb until you feel it touch the piston, then lift it a couple of mm more. If your carb doesn't have a lifter pin or it's seized (or you can't find it) then take the air filter off and use a piece of wire or something to lift the piston by a couple of mm, trying not to disturb the airflow as you do it.
5. If the engine sped up significantly the mixture is too rich, so turn the mixture nut clockwise by one flat and go back to step 4.
6. If the engine slowed down or stalled entirely it's too weak, so turn the mixture nut anticlockwise by one flat and repeat step 4.
7. If the engine sped up very slightly, it's about right.
8. Adjust the idle speed screw until it idles at about 600-700RPM again.

When I say clockwise and anticlockwise, I mean as if you were underneath the car looking up at the bottom of the carb. Turning the nut anticlockwise lowers the top of the mixture assembly.

Another way to do the fine-tuning is to turn the adjuster nut clockwise until it starts to misfire, then turn it the other way until the idle speed starts to hunt up and down, counting the number of flats between the two points. Divide the number by two and turn it back clockwise by that number of flats so it's right in the middle between the two points.

You can also use a "colortune" spark plug to see the colour of the flame and figure out from that whether it's running weak or rich.

The final way of checking the mixture setting is to take a spark plug out and clean it, then go for a decent run and take the plug out again when you get back. If the deposits on it are white, the mixture is weak. If the deposits are black, the mixture is rich. If the deposits are sort of greyish then it's set correctly. If it's oily then you have other problems...

All that setting above is just the idling setting - it only very slightly affects the running mixture - which needs a different needle profile to make any worthwhile change.

bmcecosse wrote:All that setting above is just the idling setting - it only very slightly affects the running mixture - which needs a different needle profile to make any worthwhile change.

The jet height DOES affect the running mixture - By lowering or raising it you're what part of the needle is in play at any given revs. So, working on the basis the vast majority of cars have the correct needle to start with, if you then assume the carb is in good order the jet setting makes all the difference to the mixture THROUGHOUT the rev range!

In prcatice you are only moving the jet height very slightly when adjusting the idle mix - and the needle in that idling zone is only very slightly tapered. The actual running section of the needle is however much thinner - and the tiny difference made by moving the jet is almost insignificant to the running mixture. Fuel level in the chamber has a far bigger effect!

I've always found a profound difference between the mixture jet in it's two extreme positions, in fact the manual tells you that is what it's for, adjusting the mixture!

Yes - the idle mixture.

Yes - the idle mixture.

Which sets the mixture throughout the range, In a standard set-up!