URGENT HELP NEEDED!! CARB!!

[AndrewSkinner]

Please could someone advise me on how to get the mixture correct on my morris!!??

I have totally messed it up!

In the morris manual it says turn the mixture bolt clockwise to richen and anticlockwise to weaken?? But is that from looking above or below?? in the picture they are looking at it from the side!!!!!!

When the spring above the mixture bolt is compressed is that at its richest or weakest??? and how do you know when it is right??

[Welung666]

Simplest way to get the mixture roughly right is to take off the air filter and hold the piston up out of the way, turn the mixture nut up so it is flush with the bottom of the carb where it comes inside (where the needle on the piston drops through) and then wind it back down 12 flats (2 full turns). That should be about right then. I set Phoebe's carb that way and it was perfect on the colourtune.

[AndrewSkinner]

Simplest way to get the mixture roughly right is to take off the air filter and hold the piston up out of the way, turn the mixture nut up so it is flush with the bottom of the carb where it comes inside (where the needle on the piston drops through) and then wind it back down 12 flats (2 full turns). That should be about right then. I set Phoebe's carb that way and it was perfect on the colourtune.

ok have just tried that but the little piece inside where the needle drops though but there is no movement when i do the mixture bolt up or undo it??? is this a broken carb??

[alex_holden]

The procedure is in this old thread.

When you unscrew the nut the jet goes lower, which increases the size of the opening and makes the mixture richer.

[alex_holden]

ok have just tried that but the little piece inside where the needle drops though but there is no movement when i do the mixture bolt up or undo it??? is this a broken carb??

Is the choke fully off? The jet only moves a small amount when you adjust it.

[AndrewSkinner]

Ok thanks for your help.

I have done all of the above and used bits from the other topic.

By doing what you have said it would seem as if the carb was tunned to perfection!!! everything behaves as it should until you go into the car and almost faint when you see the fuel gauge again!!

There is a tiny puff of black smoke when you accelerate quickly is this correct?

At the moment i still think that the car is averaging about 25mpg!

I have just taken it up the motorway for a quick blast, in all i have probably just done 6 miles of driving at the most and the fuel has almost dropped a notch on the gauge.

I am pretty sure there arent any fuel leaks from the tank, there is some petrol below the carb (On the floor of th engine bay) but this looks like a small leak from the carb, not enough to cause it to gussle fuel)

I dont know where the fuel is leaking from or where is it going!!

[Welung666]

Sounds just like Phoebe is at the moment, 4 miles each way to work, there and back twice a day so 16 miles a day and I've used nearly a full tank of fuel this week! This isn't counting shopping trips, sliding about in the snow Friday night and school runs though. The leak you desribe is more than likely from the small tube from the float chamber to the jet, Phoebe has a steady drip at tickover from the bottom of the float chamber, I'm sure as I run and the pump pumps harder it's more than a drip though. Another job on my list

[Packedup]

Undo the two screws that hold the top of the carb on, lift it off and gently place it to one side (make sure you don't bend the needle! The piston will try and fall out the cover, and oil will leak out the hole in the damper rod cap, so stick it on its side on a clean bit of cardboard or suchlike well away from feet, and be prepared to top up with oil at the end of teh job.

You should be able to see the jet bearing (outer brass ring when viewed from above) and the jet (inner brass ring viewed from above). Turn the spring loaded nut under the carb till the inner and outer rings are flush with each other. Then wind the nut approx 2 full turns (12 flats) "down" - Clockwise as viewed from above. The jet should move maybe 0.3mm or so (guesstimate - I know the setting when I see it) down, which is a good starting point. With it set like this, put the top assembly back on, top up with oil, and run the engine till warm (ideally go for a drive to get it properly up to temp), before following the usual tuning procedure.

If the jet doesn't move but the nut does, suspect the jet to have seized. You might be able to free it with a little wiggling, but chances are if it's stuck you'll need to at the very least remove it and the bearing to work them apart, if not buy replacement parts. You can remove the jet and bearing with the carb still fitted to the engine.

I've never had a stuck jet on a single carbed car, but I'd imagine it would make the choke feel very heavy and maybe even immobile. Only times I've had it have been on twin carbs, where there was enough slack and twist in the linkages for it not to make a lot of difference to the feel when pulling the knob out. And thinking of choke, make sure when setting the jet/ mixture the choke is fully off, and there's a small amount of slack in the cable!

[bmcecosse]

It could just be the choke is sticking on slightly. But short runs in this weather are likely to lead to high fuel consumption. Take the car for a good run - then take out a spark plug and look at the colour. If it's white - it's too weak, if it's black it's too rich, and if it's a nice biscuit colour - it's just right! Worthwhile checking if the air filter is blocked/coated with oil mist - or just fit a new one anyway. And the ignition timing needs to be set up (just not quite pinking) for best fuel economy - and the vacuum advance is very important too for best economy.

[rayofleamington]

just a quick comment - on my latest Minor it did 25mpg on the way home.
After replacing the air filter it was doing 35mpg and after leaning the mixture it made 40. It's not worth playing with the carb if your airfilter is past its best!

Obviously if you've already changed it, just ignore the comment ;-)

On short journeys in winter, 25mpg is normal. It takes at least 3 or 4 miles for the engine oil to reach full temperature and until then you are getting much more internal drag - not to mention all the extra fuel used when on choke!
You need to do well over 20 miles before you can start to tell what the normal mpg is.