Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Idling puzzle

Can anyone suggest the root cause of the following fault on my 1969 4/4?

This a 1600GT Ford crossflow with a single Weber carb, and a mechanical fuel pump, unleaded head, Shell V power fuel. Standard distributor with electronic points. Manual choke.
Car starts and runs normally initially, for maybe 10 mins. Once thoroughly warmed up though, when the engine returns to idle at say a junction, anything but the most gentle application of the accelerator causes the engine to stall. The more rapidly the accelerator is pressed, the more likely the engine stalls (with a bit of a 'whuff' sound). Gradually applying the accelerator avoids the problem. Above idle, engine response/revs is normal. In fact, on recent hot days, if the car is allowed to coast to a halt, say from 30 mph, in neutral, the engine will stall before the car actually comes to a stop. Engine idles at approx. 900 rpm when warmed up and choke is fully in.

Ignition timing and advance are correct, though engine does seem to pink a little pulling up steep hills in a high gear, on a hot day. The problem goes away in the winter, ie cold days.
Carburettor has been cleaned, and the mechanical fuel pump replaced?

Any suggestions?

Many thanks

Points a bit to a rich mixture particularly if it is OK in cold weather when the motor will run with a richer mixture, . Is there a little black smoke from the exhaust at times or does it smell a little rich? Float level not correct, worn out needle valve, etc.

I think I'd be looking for an air leak in the carb/induction area. Try spraying WD40 or brake cleaner around - it'll get sucked in if you spray the leak point and it'll alter the revs alerting you to the location.
Also maybe fuel starvation - is fuel getting throu ok? A possible culprit is a rubber hose breaking down internally - that would be worse when hot. I'd be looking at the fuel line in the engine bay area first. Float level could be suspect as suggested also.

I have had some dodgy electronic components before - if you had a condenser I'd be swapping that out to check. Not so easy with the electronic kits but if all else seems ok on the fuel side I'd be suspicious of the little box of tricks hiding in the distributor.

Good luck searching.

My experience with these Weber Downdraft Carbs is that they are very prone to junk in the carb. There is a tiny screen at the fuel input, check it out. I agree about air leaks. Tighten every nut and bolt and then give it spray. I use WD40 if nothing else is handy. Not sure if in the UK ethanol is a problem. In the U.S. Corn Farmers are making lots of money at the expense of fuel hoses etc.

I'd go along with that, for what they cost probably worth doing anyway.

When looking for air leaks I employ a length of rubber tube kinda like a stethoscope, one end to my ear the other following round the joints in the carb(s) and inlet manifolding etc. The tube can also come in handy for balancing twin carbs by listening to the tone of the airflow having one end of the tube held close to the intake of the carb..

Seem to remember Weber’s have an extra little pump that squirts fuel into the inlet when the accelerator is pressed to stop this happening. Maybe blocked, faulty.

I had a problem with one that had clear silicone sealant in the float chamber that had been used as a gasket. I cleaned the carb numerous times before I found it.

Sounds like a blockage in the pump jet. With the air cleaner removed check if, when you snap the throttle open manually there is a squirt of petrol from the pump jet. You could also check the integrity of the vacuum advance and retard hose as these can perish and cause a leak.

I had forgotten about the throttle pump. Yes I would agree that that could be a cause.

Though I think if that was the case it would still happen in cold weather.

I almost have the same problem. At times when I go to neutral to stop at an intersection the engine just stops. My mechanic has cleaned the jets on the sides of the Webber carbs on my ford Kent 1600 engine but although in garage the idling was ok when I went on a trial it stalled a couple of times when changing to neutral. The engine was running ok up to yesterday . Although it is not the solution I have also increased the idling revs to 1200 but problem still persists. Any other suggestions besides the above thread.