Old Moggy still has its little miss fire..

[CDYMOGGY]

Hi all, ive had my Moggy (CDY) on the road now since July, It sailed past its MOT with no advisories after its two year sleep. But the engine has always had a little miss fire, ive done a fair bit of work on the electrical side. Its basically all new now.

Ive fitted a new coil, new points, condenser, low tension lead, rotor arm, dizzy cap and the plugs. Ive also changed the regulator box as the old one was allowing the dynamo to put on 15v! Thats what killed three coils in the past (if you've seen my other post)

I don't think the electrical side is at fault now. Unless its the HT leads. They are surpressed sylicon leads. Not my favourite stuff, but they all check out fine on the multimeter. Can these be changed for copper core?

I think my problem lies with the carb now. Mainly the mixture. When idleing the car likes to run with no choke. Its nice and smooth, responsive and sounds lovely. But when its on the road it miss fires a little at higher revs. To which a few clicks out on the choke seems to almost cure it. So im guessing the mixture is a little weak? Or the high running jets are blocked up a bit? Im not all that clued up on the solex carb. Any advice would be great.

Cheers, Dan

[bmcecosse]

Your car has a Solex carb - with jets ??? Very non -standard then..... All other Minors run the very efficient and simple SU carb...with one jet and a tapered metering needle. Have you run a compression check on the engine?? Set the valve gaps first...

[MarkyB]

It's not just continuity you need the leads to have, they must be insulated enough not to lose the spark before it gets to the plug.
Running the engine in the dark can help to see if any are going astray, sometimes you can hear a little noise as it happens.

[CDYMOGGY]

Your car has a Solex carb - with jets ??? Very non -standard then..... All other Minors run the very efficient and simple SU carb...with one jet and a tapered metering needle. Have you run a compression check on the engine?? Set the valve gaps first...

Sorry that's just my lack of knowledge of these carbs.. It's an SU completely standard. So it has no jets.. Does anyone no roughly how many turns out the mixture should be?

I think I'll replace the leads. They have been on there for a long old time.

Dan

[bmcecosse]

Yes - have a go at the leads - although poor leads are more likely to misbehave in wet weather - and on cold starts... But worth a try! Compression check will tell you (and us) the general engine condition. http://www.ebay.co.uk/itm/HEAVY-DUTY-PE ... 3f3e84d67a

[Nickol]

Sorry that's just my lack of knowledge of these carbs.. It's an SU completely standard. So it has no jets.. Does anyone no roughly how many turns out the mixture should be?

I think I'll replace the leads. They have been on there for a long old time.

Dan[/quote]

12 flats of the large nut is the standard starting point for adjustment. Screw it right in first, then do the dozen! Do you know how to check for correct idle mixture?

The misfire at higher revs on the road could be the vacuum advance not working properly - Roy will know whether your model has such an animal.

[bmcecosse]

Vacuum advance works at low throttle settings - so not generally at high revs....although it could be forcing an incorrect 'idle' setting (if faulty) which in turn could upset the high revs running. Just how 'high' are the revs....maybe valve bounce if the springs are weak ?

[Nickol]

Vacuum advance works at low throttle settings - so not generally at high revs....although it could be forcing an incorrect 'idle' setting (if faulty) which in turn could upset the high revs running. Just how 'high' are the revs....maybe valve bounce if the springs are weak ?

Is that right? I would have thought the Vac advance has an effect at all throttle settings and was dependent on the load on the engine in relation to the air/fuel throughput in the carb?

[bmcecosse]

On wide open throttle it does nothing - that's the point, the heavily loaded engine can't take too much advance for fear of pinking /detonation - on (part) closed throttle there is enough vacuum in the manifold to pull the vacuum advance up and the lightly running engine can take advantage of that. The mech advance works purely on revs - and runs out of advance at ~ 3000 rpm.

[CDYMOGGY]

Thanks guys. I'll get the leads on order and set the carb mixture, I don't know how to set the idle mixture. Although with no choke it seems to idle nicely. It does have the automatic advance and retard, it's completely standard. Copper lines go from the carb, to some sort of valve and then to the distributor. A friend did mention bypassing the old valve (bolted to the thermostat) completely with a new piece of piping. Would that be worth doing?

It's funny you should mention pinking and running on. It does run on for a few seconds after switching off the ignition, not every time. Mostly after a long run. It fires really lumpy for a few seconds and then dies. Does that point to the timing due to a faulty advance and retard mech as well?

I haven't set the valve clearances yet. That's something I need to do as well.

[bmcecosse]

Running on is due to something glowing red in the combustion chamber - enough to ignite the mixture without the spark.... Usually excessive carbon deposits... Sometimes caused by oil burning and /or generally running 'rich' and not helped by running slightly retarded. It's not a 'valve' - it's just a little vapour trap -deemed unnecessary in later cars. You seem fascinated by the vacuum system - test it ! Remove dizzy cap and suck the vacuum pipe - you should see the baseplate move and relax as you stop sucking. Oh and be ready to spit.....