The V8 Owners Forum -

Not sure where to post this so put it in this section...........

My 3.5 cortina has a strange intermittant running problem................

start it up in the morning to go to work, starts fine, runs fine, drives fine for about a mile or two, then only at light throttle it judders/holds back, coughs and splutters and wont idle. If you turn it off for a minute and restart, its fine again and will stay fine all day even if left untill cold again. Following morning it'll do it again.

When it happens, its like the first 20mm of throttle pedal travel does nothing, push down a little more then suddenly its off like a rocket.

If I don't switch it off and keep driving it will eventually (after 5 miles or so) clear and be ok again.

If you do a short run in the morning and turn it off before it plays up, then restart, it'll never play up all day.

Its an internally stock 3.5 with edelbrock 1404 and performer inlet.
Coil is an accel supercoil.
Fuel pressure is set to 3 psi and has been since day one so its not that. fuel pressure doesn't drop off when fault occours.

I've tried a new distributor, cleaned the carb and tried different jets and rods, still exactly the same!

I really can't tell if its a fuel or ignition problem.

Can anyone help please?

I wouldn't have thought it possible this time of year but it sounds very like carb icing to me. Is this just the last few weeks or days as I guess it is getting colder in the mornings.

katanaman wrote:I wouldn't have thought it possible this time of year but it sounds very like carb icing to me. Is this just the last few weeks or days as I guess it is getting colder in the mornings.

Yep I would agree. When I experience carb icing on a old banger I had, it's just like the first 1/4 throttle has no effect, but booting it makes it go just fine.

Of course once you stop, the heat from the engine defrosts things and it all works again for a while!

Have you got a heat insulator between the carb and manifold? You could try removing that to keep the carb warmer, although it might affect hot starting or idle quality a bit.

Jeff

Just had another thought - it might be that the idle mixture is too weak. The idle jets actually supply most of the fuel needed at low speeds and light throttle. The main jets only take over when you really want to go.

Maybe the lean idle mixture is causing the problem when the engine is cold? Might we worth winding out the mixture screws by about 1/2 a turn just to see?

Jeff

Thanks for the replies chaps.

I did think about carb icing but I wouldn't have thought the carb would ice at low speeds, its been doing it for a few months now and never really had a lot of time to look into it properly but it seems to be getting worse and it's getting on my wick now so summat has to be done!

There is an insulator on the carb, this is a must as before it was fitted the fuel would evaporate out of the carb when idling in traffic and it would cut out and not restart till it had cooled down.

I'll make a temporary hot air pipe and see if that makes a difference and I'll wind the mixture screws out a bit too.