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Misfiring Moggy
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peppiB



Joined: 30 Jun 2008
Posts: 686
Location: Newcastle upon Tyne

PostPosted: Sun Dec 22, 2013 10:28 am    Post subject: Misfiring Moggy Reply with quote

Any help on this would be appreciated as it is now driving me nuts. The Moggy has a misfire (1965, 948 block with 1098 head). So far I have installed

New plugs, leads, points/condenser, rotor arm, distributor cap, coil, compression OK on all 4 cylinders, had the head off and checked the valves, dismantled cleaned and renewed needle and dashpot plunger on carb (SU), messed with the timing til I am blue in the face and STILL the b.... thing won't run smoothly. Power is way down.
Anyone any ideas as to what I have missed
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peter scott



Joined: 18 Dec 2007
Posts: 7113
Location: Edinburgh

PostPosted: Sun Dec 22, 2013 10:32 am    Post subject: Reply with quote

If your new rotor arm is black then it may be conductive when hot. Try an old rotor arm or a new red one.

Peter
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peppiB



Joined: 30 Jun 2008
Posts: 686
Location: Newcastle upon Tyne

PostPosted: Sun Dec 22, 2013 10:35 am    Post subject: Reply with quote

Thanks Peter,

So far have gone through 5 rotor arms old and new, black and red, without success. Even took the rotor out of the Landcrab as it is a known good one but still no difference.
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Rick
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Joined: 27 Apr 2005
Posts: 22429
Location: UK

PostPosted: Sun Dec 22, 2013 11:04 am    Post subject: Reply with quote

Is the misfire constant, or just when warmed up, or when running from cold?

Is there side-to-side play in the distributor shaft (ie the one the rotor arm goes on)?

There's a thin wire (the name of which escapes me) beneath the base plate in the dizzy that can get frilly, maybe that's breaking up? Is the main HT lead fully pressed into the top of the coil?

Do you have an air leak on the induction side? eg inlet manifold gasket, or perhaps the mating faces of the carb:manifold aren't level and thus letting in air?

Could there be a leak on the vacuum advance pipe?

RJ
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peppiB



Joined: 30 Jun 2008
Posts: 686
Location: Newcastle upon Tyne

PostPosted: Sun Dec 22, 2013 11:31 am    Post subject: Reply with quote

Hi Rick,

There is no play on the shaft - the distributor is 2 years old. The wire under the baseplate, a common cause of breakdowns, is new

The manifold has new gaskets, fitted when I had the head off, and I was careful to ensure the carb was refitted correctly

The misfire is bad when cold and doesn't improve much when the engine gets warm. have checked the vac advance pipe (also only 2 years old) and it seems OK. I am wondering if the diaphragm in the auto advance mechanism could be the fault now. Haven't checked but I suspect the new distributor originates in China and the number of faulty Chinese parts I have had to discard is surprisingly high (points, ROTOR ARMS especially, distributor caps and coils) I even had a Chinese made bottom pulley 'explode' on me this year making a heck of a mess of the radiator. I got my money refunded on that one!
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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Sun Dec 22, 2013 1:20 pm    Post subject: Reply with quote

Could there be an induction leak somewhere ? A blast of WD40 when the engine is idling is a good quick indicator?

Otherwise do you know someone with an engine scope?, these sort of faults are quickly diagnosed when there is some visibility into what's going on.

Dave
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NONORT



Joined: 26 Apr 2012
Posts: 55
Location: Southampton

PostPosted: Sun Dec 22, 2013 2:43 pm    Post subject: Reply with quote

Try taking out the plugs to see if there is duff one different colour etc. Before that try taking off one spark plug lead at a time to see if the misfire is on one cylinder. The moggy engine will run on three pots. The other thing is have you an old spark plug lead that you can use from say the land crab that you know is ok. Swap each lead in turn this takes out the chance of swapping one duff lead for another. Other opitions include swaping one plug at a time till you find the duffer. Its not unknown to find a new plug with a duff conection internally. I very much doubt that the fuel side of the car has any problems as it will at least start. It may sound condisending but are the leads on in the correct order 'been there done it got the tee shirt'? My car ran like this for about thrree hours! Is the missfire constant and regular not random if its random look for common components like coil to distibuter lead coil its self, points sticking I had a set that were sticking on the hinge post opening and shuting at random. ps dont give up I spent an afternoon trying to start a moggy with the rotor arm missing! My daughter had helped put in the new points 'she was five at the time'? put in her pocket to keep it safe!
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NONORT



Joined: 26 Apr 2012
Posts: 55
Location: Southampton

PostPosted: Sun Dec 22, 2013 2:48 pm    Post subject: Reply with quote

Sorry forgot to mention the condenser try ant one that will fit in the space. The morris owners club are constantly moaning about the quality of these parts particularily supposed ' Lucas' parts you know what they say 'King of the road Prince of darkness' etc
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peppiB



Joined: 30 Jun 2008
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Location: Newcastle upon Tyne

PostPosted: Sun Dec 22, 2013 5:05 pm    Post subject: Reply with quote

Sadly I don't know anyone with a scope Sad

have tried plug leads off 1 at a time and no matter which one I take off the engine keeps running roughly. It doesn't seem to make any difference (unlike when the head gasket blows and you can quickly determine where)
problem is still there using the leads from the landcrab, and the leads from the Moggy work well when fitted to said 'crab.

When removed, the plugs are invariably sooted - haven't had the thing out for a long run because of the problem so a lot of the engine running has been short bursts.

The distributor is an Accuspark where the points and condenser come as 1 unit. Have had 3 sets of those on - including 1 set where the engine wouldn't fire and on inspection I found 2 wires hadn't been soldered on.

I will try the WD40 and see if it indicates anything

I have been working on Moggies for 53 years and can honestly say this is the first time I have been stumped

very many thanks for all your suggestions
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Rick
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Location: UK

PostPosted: Sun Dec 22, 2013 5:34 pm    Post subject: Reply with quote

Is it possible to go back to a factory-original dizzy, and work forwards from there?

Out of curiosity, how old is the fuel? Just wondered as it doesn't seem to last long before going "off" somewhat. Our newish petrol mower won't start on this year's fuel when we fire it up next spring I'm sure, if this year was anything to go by.

RJ
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peppiB



Joined: 30 Jun 2008
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Location: Newcastle upon Tyne

PostPosted: Sun Dec 22, 2013 7:48 pm    Post subject: Reply with quote

I would have to buy another dizzy Rick as the original fell to bits (the auto advance mechanism fell off) Don't feel like taking the one off the landcrab as I don't want to upset it

I have been trying to sort this problem since June. The petrol station is close by and i think it was July I filled the car
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jessejazza



Joined: 18 Mar 2009
Posts: 75

PostPosted: Sun Dec 22, 2013 9:56 pm    Post subject: Reply with quote

peppiB wrote:
Sadly I don't know anyone with a scope Sad
...
When removed, the plugs are invariably sooted - haven't had the thing out for a long run because of the problem so a lot of the engine running has been short bursts.

The distributor is an Accuspark where the points and condenser come as 1 unit. Have had 3 sets of those on - including 1 set where the engine wouldn't fire and on inspection I found 2 wires hadn't been soldered on.

I will try the WD40 and see if it indicates anything

I have been working on Moggies for 53 years and can honestly say this is the first time I have been stumped

very many thanks for all your suggestions

Dizzy problem is my thought. You confuse us a little as lastly you mention the dizzy is a modern Accuspark.

I'd borrow a known sound dizzy from a moggie club friend. Then you'll know for sure.

Alternatively. I have found points and condensors poor. I have four sets of points that are dud in the garage and can't see what the problem is. I check the ignition LT by removing dizzy from car, removing king lead, and then attaching meter to -ve lead to coil and earth. Rotate dizzy cog and check each opening of the points.

Symptoms on the plugs are similar to a Newtronic optical ignition system i had on a Scimitar - somehow it fired at varying incorrect times. I stick to TAC units now which I have found well worth making up - a condensor isn't worth even fitting these days imo.
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alanb



Joined: 10 Sep 2012
Posts: 516
Location: Berkshire.

PostPosted: Sun Dec 22, 2013 10:00 pm    Post subject: Reply with quote

If the plugs are sooted it would appear to be running rich, if you have changed the carburator needle are you sure it is the correct one, they come in thee sizes (rich, normal, lean). If it's to rich the engine will run lumpy and lack performance.
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Jonv8



Joined: 28 Jan 2009
Posts: 66

PostPosted: Mon Dec 23, 2013 8:16 am    Post subject: Reply with quote

I'd not heard of these Accuspark units before a conversation I had yesterday.A family friend is having similar problems with an MG Midget with one of these fitted.My suggestion was to throw it away and fit a Lumenition Optronic kit to the original distributor.Not cheap but make so much difference to starting, running and reliability.My family and friends have several vehicles fitted with them,the latest is on a 1967 6cyl Land Rover which is going to spend the next 2 years exploring the whole of Australia...
I can also strongly recommend using a scope to diagnose ignition faults,I have a 4 channel Picoscope - brilliant tool.
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ka



Joined: 03 Dec 2007
Posts: 600
Location: Orkney.

PostPosted: Mon Dec 23, 2013 9:28 am    Post subject: Reply with quote

I have used the distributor from a later Mini. These have a module electronic ignition system and seem to be 100% reliable.
I personally am not keen on electronic ignition systems, particularly aftermarket, I am sure there are lots of people who have used them with great success, but when they go wrong at the side of the road in the middle of nowhere, you are stuffed.
I keep the points, disconnect the capacitor, (as already commented, 99% of them are duff from brand new) and fit an ignition support system, the one I use is from Maplins, a self assembly kit for under £9, that does away with the condenser, and has been 100% from fitting a couple of years ago. If it does fail, reconnect the condenser and back to the normal set-up.
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