Hi guys,

I'm new to carbed engines, and I was wondering whether I could get some help brainstorming the possible solution to a problem i'm having please?

So the car runs. But it drops a cylinder - it's not detonating properly.

- The car warms up, we took the choke down. After a while it began missing more and more, until it eventually stalled itself out. We couldn't get to the choke in time to save it.

- I've checked the plugs. They are black, so I know that there is a too much fuel in the system. Maybe a bit too much?

- I disconnected the HT lead from cylinder 1 (cylinder furthest right, looking into the bay), and the car dropped to a regular, 3 cylinder pattern. Possibly suggesting that this is the cylinder that sometimes doesn't fire.

- I have removed all the airbox and intake, and even started the engine with no airbox attached. This did not affect the running of the car.

- I have cleaned up the top half of the carb with carb cleaner. I checked the choke and the throttle connection - both function as expected. There is some adjustment to be had on the choke.

- The dizzy has oil leaking around the bottom of it, at a very slow rate. I have checked spark from all 4 of the points, and they seem to be working fine.

- I have yet to check the fuel filter.

- We are going to do a compression test on cylinder 1 tonight.

- The car hasn't been driven properly in a while. it has been started to be moved, and left to warm up. It used to miss on choke, but always ran on 4 cylinders when I regulated with the throttle pedal.

Is there anything else that I should look at, or does anyone have any ideas/advice about what might be making my car run rough?

Thanks.

Andrew.

Black dry plugs are rich mixture, Black and sticky wet for oil.

Need to turn the mixture screw a bit to lean it out slightly.

It does seem you have covered most things, get that compression tester on it and see if that shows up anything further.

Leak around the dizzy can be down to the rubber o-ring perishing.

Sorry, yes the plugs were black and dry. So definitely rich mixture. I will attempt to lean out the mixture, see what results that yields too. Thanks for the advice.

There was someone else recently who had exactly the same sounding issue as you and he too had issues with Cyl 1 cutting in/out on. Mk2 1l.

Ill have a look for his thread.

First of all, it is normal to count cylinder numbers from the timing belt end of the engine.

You say that when you removed the plug lead, the engine 'dropped to a three cylinder pattern'. This is exactly what it should do, had removing the plug lead made no difference to the running of the engine, then either 1) there is no spark to that cylinder, 2) no fuel (due, maybe to a leaking inlet manifold) or 3) no/low compression.

Your problem definitely sounds as if there is far too much fuel, had you still had the same problem with the air cleaner in place, then of course, it could have been down to too little air.

The mixture screw will only affect the engines running at tick over speed.

I would suggest that you check that petrol jets are not lose (BUT do not over tighten them). Also check the height of the petrol in the float chamber, this could be too high due to a leaking needle valve and seat, punctured float or too high a fuel pressure from the pump.

Regards.

Right. Some really good responses, thanks guys.

So I meant cylinder 4, not 1, when I was checking them. I dont know why i wanted to call it #1.. Thanks for pointing that out.

Tested for compression last night - a very solid 11bar across all 4 cylinders.

We played with the mixture screws a bit, and then noticed that the air temp sensor that sits in the airbox was disconnected at the carb end. We reattached it and fired the car up, and all of a sudden the car ran 95% better. There are still misses on occasion - I think there might be a hose or a seal on its way out - and also maybe a grounding pin as I kept getting shocks off the block. The engine earth lead is fine.

At a stage now where it'll run clean enough to pass an MOT though :)

Shock from the block...

Maybe its arcing out of the oily dizzy. Just needs a wipe inside the dizzy cap and then a new O-ring normally.

You might be able to see it at nght.

How clean/old are the HT leads?

How clean are the HT lead contacts?

Check and file/sandpaper them one at a time to preserve the firing order.

The HT leads look good. There aren't any visible cracks in them, they aren't perished at all and the connectors to both the dizzy and the plugs look and feel fine.

I'll give around the dizzy and rotor arm a good clean, and maybe see if I can seal it up a bit better. There was a bit of play on the cap when I wiggle it with my hand.