Morris Minor Owners Club

After taking my morris 1000 to a friend who works for hometune for a misfiring problem he told me that my carb was knackered, it was running incredibly rich and couldnt be adjusted any more due to a worn jet, he advised replacing the carb unless repairing it, as I have little/no knowledge of carburettors can anyone advise me on the best solution to my problem, whether replacing the jet assembly or simply buying a refurbished carb.

Hello MH,
I don't think that advice is very good. Jets rarely wear and there is so much adjustment that it is not likely to be a factor. The first thing to check is that the needle in the dashpot is fitted correctly, the shoulder on the needle should be flush with the bottom face of the piston.
With the dashpot and piston removed, adjust the jet flush with the bridge in the bore of the carburettor, then screw down the jet adjuster twelve flats, that is two full turns of the adjuster. Refit the dashpot and piston, and this should give a mixture close to ideal. Also check by putting a finger into the carburettor intake, pushing up the piston and releasing it that it falls slowly and stops with a click. This checks that the needle is not fouling the jet.
If it is still way out then further checks are neccesary. See how you go with that. The only real wear issues with S.U. carburettors are with the spindle which upsets the idle slightly, but otherwise it will still run well. Little else wears to affect running.

Alec

New SU carburetters are available from http://www.burlen.co.uk/ I recently fitted one to mine as the jets were worn and the butterfly spindle as well. I do believe they do reconditioned ones as well. New I think mine was round £100.

i changed mine as i broke it by cleaning it only could get 35 mph
i changed the needle and jet easy job to do took 30 min then set it up cost only £25 from east susex minors
if when you have the dashpot out look at the jet if eggy shaped change it and you might as well change the needle at the same time thay do ware out after a while .
when you are doing this take off the fuel pump wire run the engine when it stops the fuel chamber is nearly empty then unscrew the choke from the jet bottom undo the nut to the fuel camber (on the sied of teh carb were the fuel pipe gose to ) then change it when doing this take off teh top of the fuel chamber then clean and check teh flot is working and shutting of that bit on top of the flot .when you have done this put all back together ,take out the needle by undoing the grub screw on the side then change that as well .once all done get you mate to try to do it and it should work if it dont then you will have a damaged carb somewere in side there will be a dent or scrach there that will still let tooo much fuel in but i recon its you jet and needle .
hope thsi works for you let us know if it works
moggyminor16
1962 2 door saloon
1966 traveller (bling mobile)
1967 convertible needing a lot of loving


www.geocities.com/moggyminor16/moggyminors_moggys.html

Hello MH,
one other thing that comes to mind is that the jet is being held off in the 'choked' position. Check that the jet returns fully home with the choke knob fully pushed in. You can adjust the mixture as much as you like with absolutely no effect if the jet is not fully home.

Alec

The jet was oval shaped, but apparently very badly so, which would explain the poor fuel consumption and erratic idle, thanks for the advice.

Hello MH,
make sure that the jet is centred when you replace it, it must have been off centre for it to wear, which will also wear the needle. There is not normally any mechanical contact between the needle and the jet so there should be no wear in either in normal circumstances.

Alec

I think im going to get a pro to do it!

Hopefully not the 'hometune' lad who wants you to buy a whole new carb !!

[quote="bmcecosse"]Hopefully not the Well he said it may be cheaper and if so do that, but hes offered to do the work for free as hes a mate so i know hes not taking me for a ride.

Is anyone still contributing on this topic??

Bought a 1098cc saloon but the jet was sticking and I found it had the M needle rather than the right AN needle, so...

Just put a new jet and needle in, screwed it all together, slung it on the manifold and started it.

The good news is that it started, the bad news is that it revved really high, even cold, with no choke, and wouldn't slow down.

Guessed the needle was too deep on the carb piston so moved it out a bit. If anything the shoulder is now a fraction proud of the piston. Sounds better but still revs high.

Any ideas anyone?[frame][/frame]

Slacken off the tickover and fast idle screws (the screws with springs around them)

Put the needle back where it should be - shoulder flush with the base of the piston. Most common cause of 'rich' idle is that the needle valve in the float chamber is leaking fuel so the level is too high. When the engine is running the car it's ok since the fuel is being used up - but when idling it floods over the jet causing the richness. Worth checking!

Hello Phil,

did you centre the jet?

Alec

And indeed - as above - what Alec is getting at is, if the jet is off centre, the needle will jam on it, and the piston won't rise and fall easily as it should. Test by lifting the piston with a finger - it should slide up easily and then fall back with a nice 'clunk'.

The issue turned out to be a delightful combination:
- buggered coil, even after the RAC replaced it with a ballasted coil!
- bad jet bearing (causing jet to stick in part-choke position)
- running a 0.100" jet rather than a 0.090" jet (the clincher)
- running an "M" needle in a 1098cc car!
Once I sorted the above it started to run quite sweetly and now goes like the clappers.

Now then, who can explain a knocking from the o/s torsion bar on bumpy ground??

If it ain't one thing....

A ballast coil is definitely not right for your Minor. Refit the old coil - I'm sure there is nothing wrong with it. How on earth did it get a 100 jet in the carb ? It must have been ENORMOUSLY rich - so rich I honestly doubt it would run at all....... Relative to that 100 jet - the M needle is of no consequence whatsoever. I think someone is 'puffing up' the problem.......

a knocking from the o/s torsion bar on bumpy ground??

See which way round the master cylinder bolts have been fitted, if the nuts are toward the torsion bar it can knock on them.
This is why the head size of the bolts is reduced.
Otherwise look at all the suspension joints for play including the shock absorber bolts.