My car has been acting strange for the best part of two months now. It starts fine on the choke and once warm ticks over ok but when I stop for example at a supermarket and come back to start the car again it doesnt run and keeps cutting out. Only after driving for a couple of miles does it then tick over again when stationary. This problem is made far worse when its raining (which it seems like it has been for the last 6mths in the uk). I recently turned the tick over screw up on the carburettor which has helped a bit. I have also checked the inside of the distributor cap for moisture but its fine (I recently fitted a new condensation shield on it). I also had my battery checked today which is apparently holding its charge ok but is on its way out. The last time I replaced the entire ignition system was nearly two years ago...

Any ideas as to what might be happening will be gratefully recieved?...

If the motor will only run in neutral when you keep the revs high and stops as soon as you try to get any gear, it could be the idle solenoid in the carburettor. You need to unscrew it and use a test lead to check that it clicks every time it gets a current. The solenoids are still available if you need a new one.

Thanks, I will endeavour to do what you've said with the aid of a professional mechanic. I dont understand why the problem is made far worse when it's raining though?

What car/engine? Could be an air leak.

Its a 1988 Volvo 340DL 1.4. I have looked through the extensive portfolio that Mac kindly sent me about the Weber Carburettor on my car and it seems there isnt an idle solenoid on it. It's interesting that you say it could be an air leak as I recently removed the air-filter pan to see if anything was amiss around the carb; Two of the screws on the top of the carb were very loose! I also noticed reading macs portfolio last night that the 3 posts that the air-filter pan bolts onto can become loose through over-tightening; One of my 3 posts is like this and I had to seal it tighter in place by using locknut compound and also not over-tightening that specific bolt. Maybe my air-filter pan isnt tightly sealed enough thus letting in air?...

Don't worry about the air cleaner pan not being sealed to the carb top - it will make no practical difference to the running.
However be very worried by a missing idle solenoid - that really will screw up the low speed running and idle!. The idle solenoid carries the calibrated idle jet and it's lack will render it impossible to correctly set the idle mixture and speed.

Mac.

mac wrote:Don't worry about the air cleaner pan not being sealed to the carb top - it will make no practical difference to the running.
However be very worried by a missing idle solenoid - that really will screw up the low speed running and idle!. The idle solenoid carries the calibrated idle jet and it's lack will render it impossible to correctly set the idle mixture and speed.

Mac.

Mac, on the diagrams of my carb that you sent me in the portfolio it doesnt indicate an idle solenoid?

My carb only has two screws; one on the right looking at the carb from the passengers side which is the tick over screw and then one to the left of it which is the mixture screw...

The idle solenoid is the bit of the carb with a green with red trace wire going to it.

idle mixture too lean?

It cant be as I've turned the tick-over screw up (the screw on the right looking at the carb from the passengers side of the car) so the car is running faster! I suppose it wouldnt hurt to turn the mixture screw up aswell? (the screw on the left looking at the carb from the passengers side of the car)

Could someone please supply me with a photo of the idle solenoid for my weber carb - 1988 1.4 Volvo 340DL ???

Set idle to 1500rpm~ then turn mixture screw in till engine slows down, then turn mixture screw out very slowly to get max rpm out of engine, then turn idle down to 900rpm~ your mixture is now set.
you can lean it out a little* if the idle is now too high and the idle screw is at end of its travel.

Im guessing by idle screw you mean the "tick-over" screw on the right of the carb and mixture screw being the one to the left of it? Im also guessing that turning these screws clockwise increases the mixture and tick-over speed? It would help if someone could post a photo or diagram?

Also, can I set the two screws with the air-filter pan still on or do I need to remove it?...

If the car was running fine before and isn't now then its not an adjustment issue IMO. You really need to get that idle solenoid sorted before you do anything else. If you remove the air filter completely and unbolt it from the top of the carb, so you're just looking at the carb directly, there's a very obvious 'electrical' thingy on the side of the carb body. It has a hexagonal part on its body so you can unscrew it with a spanner and a single spade connection to it. From memory the wire going to it is blue and red striped but I might be wrong on that.

If you put the ignition on/engine not running and disconnect the wire going to it and then reconnect, you should hear a distinct 'click' sound as it pulls the needle back. The idle solenoid on that carb also contains the idle jet and can easily get gunked up with fuel varnish and stick shut, or else the coil fails and doesn't pull it in the first place. Assuming you get a click then all is well and you can proceed with carb adjustment.

If the solenoid does NOT click then further investigation is needed. You need to unscrew the solenoid from the carb body. Then, with clean hands, look closely at the business end. There is a brass piece with some numbers stamped into it and a very small hole, pull this off the main body very carefully, there will be a plunger and spring inside which you do NOT want to lose! Once you have it apart, give the brass jet a good spray with carb cleaner spray get it really clean. You should also do the same to the metal plunger inside the solenoid body, clean the end really well to make sure it can't stick shut.

Once you've done that put it back together, and either run 12V across it or screw it back carefully into the carb (don't overtighten) and do the test with the wire and ignition on again. If it still doesn't click then the coil has failed and you'll need to buy a new solenoid.

Come back to us once you've done that and we can then guide you further.

Thanks Pettaw, I really appreciate your advice and patience. My car seems a lot better now that the weather isn't so wet but I will still run the first test you mentioned as Im curious. Where would I obtain a new idle solenoid should I need one?...

Also if I discover my idle solenoids ok and then proceed to tune my car is it possible to do it with the air filter pan still in place? Im guessing that when I turn the "mixture" screw up that the car will start to run faster so I'll need to turn the "tick-over" screw down?...

set the carb up with the filter off.
If you put your hand 90% over the air intake there should be no inrease or decrease in rpm.
if rpms rise then the mixture is too lean, if the rpm's fall the mixture is too weak. you should be able to all but block the intake without changing the rpm: the airfilter is best left off to set idle mixture so you can do this test.