Morris Minor Owners Club

Well, that didn't work. Half my reply suddenly disappeared. So here is the full thing again:

Well, all was not what it seemed. When I got the carb off the car, the adjusting nut was the right way round. I think the shiny metal at the top of the jet base might have looked like the top of the adjusting nut. In any case, that wasn't the cause of the lateral movement in the jet. I took some pictures when I had the jet etc. disassembled. I think you'll see there is nothing amiss with the carb. I reassembled everything again, and the piston stuck firmly at the bottom of its travel. I recentred the jet and it was good - until I reattached the arm for the choke. Even that little bit of lateral pressure was enough to make it bind again. I slackened the lock nut slightly and recentred it with the choke arm attached and that seemed to do the trick, but it suggests there is still lateral play in the assembly. But I got it all back on and still got that nice metallic clunk when the piston went down. However, as soon as I started to adjust the mixture, the idle went rough again. There is no way to keep the mixture consistent and the flow of fuel into the carb mouth smooth. I managed to adjust the mixture eventually, but even then the engine started to die after it had been revved up and allowed to go back to idle. I think it might be time to bite the bullet and spend £150 on a recon carb from ESM. But I think I'm going to sell the car instead. Today when I went out to test drive it I got caught in a downpour – and the wipers stopped working. Maybe this car and I are not meant to be bosom buddies...

Many thanks for the picture and explanation.
It is always difficult to make an accurate diagnoses from a distance.
Two things before you spend.

1. Is that choke link arm bent out of true? If it is it may be pulling the jet to one side so jamming the needle in the jet.
The link should fit against the side of the jet without pulling the jet in any direction.

2. Is the jet itself bent? Again it may be pulling against the needle and causing the needle to jam.
Put a steel rule against the side of the jet to determine if true.

Please do not give up on the car - the carb and wipers are only small problems in a world with big problems. They will be overcome and you will be able to enjoy.
Phil

No, the arm only exerts the pressure it should because it is spring-loaded. It sits nicely against the side of the jet when extended. The jet is brand new and not out of true.

The thing is, these may be minor (ahem) problems, but I have had almost no running out of the car for 18 months. First a big end went on the M40, then this misfire started after I repaired the engine. I've had a mechanic look at it and he's none the wiser. We thought we had it licked, but it came back with a vengeance. The hesitation goes from almost imperceptible sometimes to like riding a bucking Bronco on others. And the fact that it's inconsistent is the most problematic of all. I've replaced all the ignition pieces, the head, rebuilt the carb... And still it's there. Yesterday it was back, after wooing me into thinking it had gone when I drove it Saturday (immediately after reinstalling the carb for the fourth time). And it was doing it all the time, at all speeds, whether under load or not.

So the ad goes onto Classic Car and Ebay at the end of the week. Time for someone else to have a go!