Weak spark

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Doug G
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Weak spark

Post by Doug G » Fri Aug 29, 2014 17:42

My Mini Moke provides a tiny spark at the spark plug.

What generally is the main cause and what steps should I take to correct it?
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spider
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Re: Weak spark

Post by spider » Fri Aug 29, 2014 20:00

Often with this sort of thing, it'll be some very small obscure item that you've overlooked or assumed to be OK.

Probably the first thing I'd check, remove the main HT lead from the dissy cap and see if I'm getting 'full spark' from that, that will narrow it down.

If not then check the Points to make sure they are opening to the 0.014 - 0.016" that they are supposed to and that the contacts are clean and making. If you've had the points out in recent times, be sure all the insluators are in place on the moving part. Also check the LT wire to the Points and condensor, have a reall good look at them, if they are on the old side, the insulation gets hard and brittle, so will crack. There should also be an earth wire inside the dissy, it's only small and usually these were not insulated, one end of it is usually under the same screw that holds the condensor in place.

If that's OK, then check that the full 12V is getting to the Coil.

If that checks out, then it could be that either (or both) the coil or condensor are nearly karput.

If you do find you get a good spark straight off the coil, then it's in the HT circuit. Check the cap is clean, not cracked and that the little carbon in the centre is still there and not missing or jammed. Check the rotor button too, that it is also clean and not cracked. With the price of this struff being so cheap, it's often easier to replace them.

The only other things left are the HT Leads and the spark plugs themselves.
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Doug G
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Re: Weak spark

Post by Doug G » Sun Sep 07, 2014 15:27

spider wrote:Often with this sort of thing, it'll be some very small obscure item that you've overlooked or assumed to be OK.

Probably the first thing I'd check, remove the main HT lead from the dissy cap and see if I'm getting 'full spark' from that, that will narrow it down.

If not then check the Points to make sure they are opening to the 0.014 - 0.016" that they are supposed to and that the contacts are clean and making. If you've had the points out in recent times, be sure all the insluators are in place on the moving part. Also check the LT wire to the Points and condensor, have a reall good look at them, if they are on the old side, the insulation gets hard and brittle, so will crack. There should also be an earth wire inside the dissy, it's only small and usually these were not insulated, one end of it is usually under the same screw that holds the condensor in place.

If that's OK, then check that the full 12V is getting to the Coil.

If that checks out, then it could be that either (or both) the coil or condensor are nearly karput.

If you do find you get a good spark straight off the coil, then it's in the HT circuit. Check the cap is clean, not cracked and that the little carbon in the centre is still there and not missing or jammed. Check the rotor button too, that it is also clean and not cracked. With the price of this struff being so cheap, it's often easier to replace them.

The only other things left are the HT Leads and the spark plugs themselves.
The chap reconnected everything. Told me to get spark plugs with a '5' (hotter) in them rather than the ones with the '6' that are in.

It fires up straight away.

What are the correct plugs for a 998cc Moke (circa 1973) engine?

Image
Last edited by Doug G on Thu Sep 18, 2014 3:37, edited 1 time in total.
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Doug G
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Re: Weak spark

Post by Doug G » Sun Sep 07, 2014 15:51

The ones I have put in (at present) are

NGK BPR5ES
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Nigel(no top)Sykes
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Re: Weak spark

Post by Nigel(no top)Sykes » Sun Sep 07, 2014 18:41

I always stick with champion ones. N9Y. A lot easier to remember than those NGK numbers
At least can add up

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Doug G
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Re: Weak spark

Post by Doug G » Sun Sep 07, 2014 19:34

[img]
Cross Reference Spark Plug

Referenced From NGK Catalogue

Possible replacement spark plugs for CHAMPION - N9Y

NGK

Part Number: BP6ES

- See more at: http://sparkplugcrossreference.co.uk/12 ... ZqfMK.dpuf[/img]
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Tim
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Re: Weak spark

Post by Tim » Mon Sep 08, 2014 0:41

I run spark plugs that are one step hotter than standard, it runs much better with them. I put it down to the rubbish fuel we're served up these days.

Tim
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Re: Weak spark

Post by spider » Mon Sep 08, 2014 0:53

Tim, it's actually recommended to run one heat range hotter with unleaded fuels, though I have to say, I don't.

Doug, so why did the plugs give a weak spark? Where they fouled (really black with carbon)?
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Doug G
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Re: Weak spark

Post by Doug G » Mon Sep 08, 2014 21:05

spider wrote:Tim, it's actually recommended to run one heat range hotter with unleaded fuels, though I have to say, I don't.

Doug, so why did the plugs give a weak spark? Where they fouled (really black with carbon)?
They were really fouled. I put that down to the fact that in trying to start the engine we 'flattened' three batteries and ran a jump start.

MORE IMPORTANTLY (now the Moke is running) :


The exhaust smoke is rather BLACK at present.
chap did alter the timing a bit.

Any suggestions what to do to get it 'less' sooty' ?
Last edited by Doug G on Mon Sep 08, 2014 21:11, edited 4 times in total.
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Doug G
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Re: Weak spark

Post by Doug G » Mon Sep 08, 2014 21:09

Found this and think it could be the bit I highlighted in red:
Exhaust Color Diagnosis

Exhaust color diagnosis.
Blue/Gray Smoke: Blue/gray exhaust smoke is an indication of oil burning in the combustion chamber. These are possible symptoms and causes:

Valve Seals: Leaking valve seals will cause blue/gray smoke at startup because oil leaks past the seals into the cylinder after the engine shuts down.

Valve Guides: Excessive clearance between the valve stem and the valve guide allows oil to leak past the gap into the cylinder.

Piston Rings: Worn or damaged piston rings will cause blow-by resulting in blue/gray smoke.

Worn Cylinder Walls: Worn cylinder walls cause blow-by resulting in blue/gray smoke.

PCV System: A stuck closed PCV valve will cause excessive crankcase pressure resulting in blue/gray smoke.

Black Smoke: Black exhaust smoke is an indication of a rich fuel condition. These are possible causes:

Fuel Injectors: A leaking or dripping fuel injector will cause a rich fuel condition.

Fuel Pressure Regulator: A stuck closed fuel pressure regulator will cause a rich fuel condition.


Fuel Return: A restricted fuel return line will cause a rich fuel condition.

White/Gray Smoke: White exhaust smoke is an indication that coolant is burning in the combustion chamber. These are possible causes:

Cylinder Head: A crack in the cylinder head (around the coolant jacket) will cause coolant to enter the combustion chamber.

Engine Block: A crack in the deck of an engine block near the coolant jacket will cause coolant to enter the combustion chamber.

Head Gasket: A damaged or blown head gasket will cause coolant to enter the combustion chamber resulting in white/gray smoke coming from the tailpipe.
Could it be that the electric fuel pump is too powerful?

That there is no return line for the fuel from after the pump?
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Tim
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Re: Weak spark

Post by Tim » Mon Sep 08, 2014 22:59

They often are, but its unlikely to be the cause if the carburettor is working OK. If the fuel pump is supplying too much fuel it should still be regulated by the float valve. There's no fuel return, it just dribbles out the hole on top of the fuel bowl on the side of the carby, and runs down onto the hot exhaust manifold. This is not ideal, but normally the engine would still run OK.

Black smoke is usually a sign of too rich a fuel mixture, i.e. the carburettor needs adjusting. This is where I admit defeat. Anyone can wind the jet holder up or down to change the fuel mixture, but getting it just right across the whole rev range is a dark art that I never mastered. It probably doesn't help that my carb needle has been filed so much that its almost triangular.

Tim
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Re: Weak spark

Post by spider » Tue Sep 09, 2014 9:21

Actually, with respect here tim, Doug, it maybe your electric pump. For example, many of the Facit branded ones have too high a pressure for the SU. The recommended pressure range is 2 - 3 psi, I have found some popular models of the Facits have around 5 - 5.5 psi, could be worth checking. A little while ago I did look for a Facit that would be 100% suitable for use in a Moke, of the 300 something models they do have only one I found was suitable, but wasn't stocked by Facit, only made to order :evil: There were a few others that you might get away with, but the main problem with their lift range was too small, or those with enough lift had too high a pressure.

Also, check the condition of the Air Filter. We used to often find with a stock exhaust pipe, combined with a Rod Shift Gearbox and the engine steadies fitted thereto, that exhaust leaks where the pipe meets up with the cast manifold were common. Some of the leaky exhaust gas gets in to the air filter and clogs them up pretty quick.
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Doug G
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Re: Weak spark

Post by Doug G » Tue Sep 09, 2014 11:20

Strange as it may seem, for me :D , I have a Facet electric fuel pump #40105, Solid State, 2.5 3.5 psi.

Awaiting (for many many months) to be installed.

Will have to get out the tools and just do it.
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Re: Weak spark

Post by Nigel(no top)Sykes » Tue Sep 09, 2014 16:59

Surely the fuel pressure is a bit pf a wild goose chase. The engine will only suck as much air/fuel through the carb as it needs, the on
Y thing that will see the too high fuel pressure is the float chamber and it'll deal with it by dumping the excess fuel all over the floor via the overflow pipe.
Isn't the "too high pressure/fuel return pipe thing" of more relevance in an injected engine ?
At least can add up

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Doug G
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Re: Weak spark

Post by Doug G » Tue Sep 09, 2014 21:26

Well I think that the lower supply pump will be better in that it will also save fuel. :lol:
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