T25 Stalling at lights and roundabouts

[paulwilde]

Hi all,

First, I am very aware this particular problem is well documented on this website, but I have a couple of other questions that I'd just like some clarification on.

So I have a 1989 T25 1.9 Petrol Waterboxer, and it has started to stall when slowing down at junctions, lights, roundabouts etc. It's always been a bit unhappy when idling, but this was way worse, trying to drive home from town was a nightmare at rush hour! I guess it is largely a problem with temperature as after 20 mins things became a little more reliable. Still, I don't want this happening all the time.
Obviously I have done some reading and as such have sprayed the carb with carb cleaner, and even fitted a new fuel pump. I also checked the spark plugs which were covered in carbon, these were new last year so I have cleaned them off. A drive down to the shops it did stall at a junction again, but only once. Still grumpy when idling.
So when I got back I took a look for the mixture screw, found it, and adjusted it with the engine running and things started to settle down quite nicely, the engine actually sounds quite good at idle now. Took it for another drive around the town and things seemed good.

After all that long winded stuff, my question is... Does unscrewing the mixture screw let more or less fuel or air into the engine? Is it air or fuel it controls? My spark plugs were so black and I the screw was quite far in so I'm hoping the tighter it is the more rich the engine is? I've adjusted the screw to about 4 1/2 turns out from tightest.

Also, I bought a Colortune in the hope to tune things a little, but the engine wouldn't remain running when the Colortune was connected, I'm guessing I need the Long-Thread adaptor which I have ordered, but it looks like the "spark" area of the Colortune is quite a way up the thread, is that right?

Many questions, sorry, good thing these T25's are a labour of love, eh?

Thanks all!

[Aidan]

there's a co adjustment screw that controls fuel and there is an idle speed adjuster, the one sticking out towards you, sounds like you have just turned up the idle to the correct place; as long as it is stable and not much temp dependent than that should be fine, if it idles fast now when hot it may be there is something else out of adjustment - I don't think the colourtune stuff works on a flat four, easier to use a co meter and your nose and ear

[paulwilde]

Thanks, I did have a little turn of the screw that's sticking out towards me but didn't seem to do much, certainly no difference in the sound of the engine.
Took it for a little drive today, little grumpy starting up, it stalled after idling for about a minute without going anywhere- I could hear it about to stall. After that and starting up and keeping foot on gas for about 10 seconds it seemed much healthier so hoping it's just a temperature thing.
drove it for about 3 miles then parked at a shop, no problems. Engine started again fine but when reaching a junction it stalled again, each time I stopped on the way home it stalled. Once home, I left the engine running for 10 minutes then went for a mile drive around the village, still stalling at every junction/lights/turning.

I think the engine itself sounds fine, sounds happy once running, but I guess there has to be something up with the carb and/or choke.

Another question, I've heard it's a good idea to bung the breather hose that goes from the rear of the carb to the air filter, in the UK, is that right or not worth bothering with?

[paulwilde]

I thought I put this in my original post but guess I forgot...

The top part of the carb, under where the air filter connects, was fairly dirty too. I've also just taken another listen and their seems to be a hissing sound coming from the engine bay, can't tell exactly where from yet but going to try to test my vacuum hoses to make sure they're not cucking in air.

[paulwilde]

Another update from me.

So I decided to take a look at the vacuum hoses - they seem fine, sucking on them whilst blocking the end and no air escapes.
However, I did try to suck on the hose when still connected to the choke pull down unit, and this didn't seem to do anything. Also, manually moving this pull down unit doesn't move the butterfly valve at all...
I took the bi-metallic strip enclosure off and it looks like the choke arm (that connects to the bi-metallic strip) is at rest in the wrong place, I re-connected it all, correcting the positioning and now manually moving the pull down unit moves the butterfly valve. Adjusted the movement so it opens the butterfly valve from closed to 3.5mm (as documented) and things eems to now be work a lot lot better, touch wood!

However, still when sucking on the hose connected to the pull down unit doesn't move it, should it? Should I be sucking harder? Looking for a replacement pull down unit as I suspect its not working 100%, bit difficult to find online now. If anyone knows where I can get one please let me know!