Morris Minor Owners Club

I had the car out yesterday and while out on the road I tried to tune the carb.
For the first 30miles I didnt touch the carb, and the car was running a bit "chuggy", I would describe this as the driver having a slight rocking motion, while driving. Also wasnt very smooth at taking off from a stand still, Throttle needed pressed very gently, a quick press of the throttle would have made the engine More "Chuggy"

So on my way home again I turned up the revs and turned the air mix nut on the bottom of the carb, this seemed to make the car run a bit smoother, but 3 times on my way home (30 mile trip) The car chugged a bit then the engine cut out completely.

I turned of the radio to listen to the engine, and when I turned the ignition on I could hear the fuel pump clicking faster than normal, then she would start again no problem, This happened 3 times over 30 miles.

After the 2nd cutout I popped the bonnet and my car has an inline fuel filter fitted (not by me),
the filter had no fuel in it, after turning the key the fuel pump clicked again as before,

Got home parked the car in the garage with engine running, and tick over was too fast in my opinion.

So my conclusion is, Engine revs were too high, thus meaning fuel pump couldnt pump petrol fast enough and engine was burning it to quick for the pump to replenish.


Has anyone got an idiots guide on how to set the carb properly, ie air and fuel mix.(I take it this is what the problem is)


Thanks Mark

The pump can EASILY keep up - if it's working properly. Clean the pump contacts - and check if there is a vacuum in the tank.

How do I check if there is a vacuum in the tank.

It didnt cut out until I started fiddling with the carb.

vacuum in the tank can be found by taking the fuel cap off. if there's a loud hissing/sucking as air rushes in, then there was a vacuum. if that's the case then the vent in the cap could be blocked. my dad had that problem when he fitted a nice shiny locking petrol cap, but didnt think to check if it had a vent hole in it!

My car has the twist on cap that is attached to the filler hose with a smsll chain.

There is no hole in this cap.

they breathe through a double skin in the cap. just to rule it out, have you taken the cap off? i think if there was a vacuum in the tank you wouldn't be getting any fuel at all, so it probably isn't that. can you reverse the things you did the other day with the carb? i can't see how the idle or the mixture would make it cut out tho. peculiar!

If the air vent in the filler cap was blocked the distance the car would run before cutting out would depend on the amount of fuel in the tank. The fuller the tank the quicker the vacuum would build up in the small amount of air in the tank and the sooner th engine would cut out. On a nearly empty tank the engine would run a considerable distance before building up a vacuum and cutting out. All to do with the fact that you can compress a gas but not a liquid

Mike I drove 8 miles and filled the car with petrol, it was about another 24 miles after that when it first cut out.

It's worth checking for the vacuum then........

So for me to check the Vacuum do I need to start the car and let it run for a while, then turn it off and open the filler cap and listen for a hissing noise

That's the idea - but it would need to be taken for a run - because idling would use very little fuel.

Ill try that tomorrow then.

Are you sure you didnt adjust the mixture nut too far? Your symptoms sound rather like a very over rich mixture......not sure about the cutting out though...

See thats what I thought. Because it never played up til I adjusted the settings on the carb.
And like I said before it was idling too fast when I got home. So I thought I turned the idle screw too far.
This was why I asked for an idiots guide on how to tune the carb properly.

screw the nut on the bottom of the carb right in,then unscrew 12 flats of the nut.this is the basic setting for the mixture and the engine should start.lift the pin on the side of the carb slightly untill you get a change in the engine speed.If correct mixture ,it should rise slightly then fall back(While you hold the pin up). If it rises and stays high too rich screw the nut in a bit if it falls or stalls the engine too weak screw it out a bit,Without a rev counter,the best way of setting the idle speed is to set it on the slow side put all electrics on push the clutch in so that the engine is under max loading ,if it still runs progressively turn the idle down untill it stalls then progressively increase it untill it ticks over comfortably, its dificult to explain the idle speed but it does come after a while that you just know its right by the sound of the engine.The pump should easily cope with the demands of the engine.check filler as said,air leaks into the system,float valve ,float level,take the top off the carb and lift the chamber and pin off and look down at the jet you should see fuel just below the top of the jet,if the pump is ticking away then that usually means that its healthy

screw the nut on the bottom of the carb right in,then unscrew 12 flats of the nut.this is the basic setting for the mixture and the engine should start.lift the pin on the side of the carb slightly untill you get a change in the engine speed.If correct mixture ,it should rise slightly then fall back(While you hold the pin up). If it rises and stays high too rich screw the nut in a bit if it falls or stalls the engine too weak screw it out a bit,Without a rev counter,the best way of setting the idle speed is to set it on the slow side put all electrics on push the clutch in so that the engine is under max loading ,if it still runs progressively turn the idle down untill it stalls then progressively increase it untill it ticks over comfortably, its dificult to explain the idle speed but it does come after a while that you just know its right by the sound of the engine.The pump should easily cope with the demands of the engine.check filler as said,air leaks into the system,float valve ,float level,take the top off the carb and lift the chamber and pin off and look down at the jet you should see fuel just below the top of the jet,if the pump is ticking away then that usually means that its healthy

I followed your instructions today, and after the car had cooled down, I was able to start the car without the choke out, (I was able to do this before I changed the carb)When the original carb was fitted, and I started the car it was very responsive when the throttle was pressed, but when I changed the carband pressed the throttle it started playing up, until now by following your instructions so in my opinion Im going in the right direction, and things are improving.

I think I may have the Carb set up to run properly now, fingers crossed

Check the plug colours after a good run !

After setting the carb yesterday, I took the car out for a run, and it is worse than before, its now cutting out around every mile or so, this is doing my head in, the fuel pump is about 2yrs old, could it be knackered already, ive also got an electronic ignition kit fitted, the part that replaces the points and condensor, would this be a contributing factor.

I was looking on BMs site and they do a conversion kit to change a standard electric fuel pump to electronic, seeing this part being available, made me think that maybe my new ignition kit had summit to do with the car cutting out.

You said you had the carb set correctly! You can't just turn it down 12 flats - and expect that to be correct. You must twiddle it up and down until you get the smoothest idle- same with the ignition system - swing it back and forth to get smooth est idle. Then road test to check for pinking (advance till it pinks then retard slightly so NO pinking) and check the plug colours. DO NOT convert the fuel pump to electronic - there is absolutely no need. I'm not in favour of electronic ignition either........I much prefer good old reliable points! Your problems may be caused by faulty rotor arm or dizzy cap - or HT leads - or spark plugs (how old/what make & number) - or coil connections. There is no easy answer - it takes detective work to find the problem!

I turned the nut on carb 12 flats then adjusted it some more until it idled smoothly! I also loosened the clamp on the dizzy turned it to get the fastest idle and adjusted the advance/retard. Dizzy cap an leads were replaced 2 years ago. Plugs were replaced last year. When the car cuts out, its like its getting starved of fuel. Before it dies it chuggs a bit an if throttle is pressed nothing happens.

So I stop at road side turn ignition on and off, and the car wont start until the pump starts clicking again.
After turning the ignition off and on again it takes about 10-15 seconds for the pump to start clicking. And when it does it clicks very fast.

Im thinking the pumo is at fault