Ignition timing for 2l spread bore

[Scallops]

Folks - Killer and I had Matilda running pretty well on sunday - just the occasional backfire when cold and flicking the accelerator. The carby had been cleaned as best I could, with a new spindle but the mix knob and idle screws were not adjusted properly. But it went better than ever before - backfires went away once warm. But after an attempt to set the ignition timing and adjust mix/idle position on the carby, it backfires dreadfully.

One theory is that perhaps the carby is blocked and needs to be pulled down and cleaned out. (It has been off the vehicle for months, was cleaned in petrol and had carby cleaner shot through the bits I could access without pulling it all apart) Another is the timing is wrong...I think we adjusted it to about 10 degrees BTDC and then we had the dramas.

I read elsewhere this should be 15 degrees??? But I understand that backfiring can be due to retarded ignition timing (and air/fuel mix too weak), so I'm confused, especially as it drove pretty well the day before.

Anyone know the angle? And might the ignition timing being wrong cause backfiring?

[Scallops]

15 degrees compared to 10 degrees - is that retarded or advanced?

[wrinklearthur]

Hi Scallops

An old dizzy can be worn in the shaft and any wobble there, can upset the timing by a huge amount by the varying the points gap, check that, then at the same time look at the balance weights, the vacuum linkage and the plate that it operates, making sure that their movement is free and not sticking any where.

There is a flexible wire that earths the moveable plate inside to the body of the distributor, if this has gone open, the earth path is then down through the bearing and the arcing that it can cause, puts the spark anywhere in the timing.

Back fire can also be caused by a leak of air through the manifold gasket.

To test, carefully spray a little volatile gas such as aerostart around the intake manifold gasket joint, do this while the motor is running at a fast idle and listen for any change in the rhythm of the idle.

Needless to say do this test outside well away from other objects, do make sure that your insurances are up to date and the wife is well off.
Oh yeah, but don't tell her! otherwise she may be hiding behind the car with a lighter! :TIC:

Cheers Arthur

[wrinklearthur]

15 degrees compared to 10 degrees - is that retarded or advanced?
Hi Scallops

The spark should occur before top dead centre, as a rule, the spark should be advanced more for poorer quality fuel.

Cheers Arthur

[Scallops]

Thanks Arthur - but I think I know what the problem is now...especially as it was virtually fine 24 hours earlier....I now know that 10 degrees is retarded from where it was...and retarded timing can cause backfiring....first thing to do is advance the timing again before I take the carby back off.


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[wrinklearthur]

Thanks Arthur - but I think I know what the problem is now...especially as it was virtually fine 24 hours earlier....I now know that 10 degrees is retarded from where it was...and retarded timing can cause backfiring....first thing to do is advance the timing again before I take the carby back off.


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Hi Scallops

It isn't popping from the exhaust is it?
That cause is by a burnt exhaust valve and/or seat, that is a quiet different thing to backfire though the carby, a burnt valve could be a highly probable cause of your troubles

Backfire is the incoming manifold mixture being ignited,by the too far advanced ignition, this is caused by the inlet valve not being fully closed for the cylinder under compression.

The ignition being too far advanced, also causes the mixture charge in the cylinder to burn more fully before top dead centre, this causes pinging or rattle when the motor is pulling hard up hill or accelerating.

On a motor that has trouble cold starting, retarding the spark stops kickback.
This is a lesson learnt the hard way if you try crank start a motor with too lean a mixture and with the timing advanced.
They are not joking when they say, that you keep your thumb out of the way when using a crank handle, it is for this reason!

the inlet valve not being fully closed

There is a whole host of reasons for this to occur;

Timing issues, as we have just discussed.

Burnt inlet valve seat, not impossible but unlikely.

Sticking valve stems from a build up of crud from a life time's history, a top overhaul and decoke fixes this.

Bent valve stems, unlikely, unless the motor has been drowned.

Timing chain problems, allowing the camshaft to lose it's timing position in respect to the crankshaft, can happen if the motor is very worn and sick, so unlikely in your case.

Cheers Arthur

[Scallops]

Also, I now realise the vac advance knob was adjusted instead of something inside the distributor.....so I'm confident the problem is not with the carby or any other mechanical parts....because the vehicle drove fine the day before, so I think we'll simply start by undoing what we did last night.


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[Scallops]

Well, after playing with the vac advance knob and the mix crew, I've got it to rev without backfiring! Stay tuned (pun intended)...

[dennisS1]

Hi, there are 2 Philips screws that hold the plate that the points etc sit on, you will see them when the cap is removed. They come lose and give all manner of problems.
Measure your point gap pulling the shaft towards the points as wear in the shaft bush will give problems.
"Remember 90% of all fuel problems will be ignition."
Dennis

[Scallops]

Well, I'm now totally confused! The vehicle might not backfire at idle and revving, but drive it and it's a different story. Just can't understand how it was so close on Sunday to be as it is now.

Cleaning out a carby - how far do I need to go? Pull every little bit out? I've taken the bit off that holds the float and cleaned that out. Shot carby cleaner everywhere I can see. But maybe theory 1 is right and it's stuffed up with gunk.

Seems there are so many variables. I'm going to stick to my day job and admit I have no clue.




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[incisor]

has the condenser let go?

cleaned and gapped the spark plugs?

is it fresh fuel?

you should be able to idle the thing at about 1000rpm, and move the distributor till it is revving at the highest speed you can get it to on that idle setting, then retard it about 5mm on the circumference.

it should run at that without to many problems, if it doesnt then you need to be looking elsewhere, such as vacuum diaphragm, age of fuel, condenser, points gap. low voltage wiring to points, or cracked distributor cap...

[Scallops]

It idles fine. It has new fuel in a new stainless tank. When it's revved, it backfires through both exhaust and up into air box.

I suspect multiple issues.

Just seems odd that it was so close to fine one day then after adjusting the timing and mix/ idle it's shot. And these things were done by Blknight, not a muppet like me!


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[series1buff]

It's useless stuffing around with the timing if the spark is weak and/or the carby isn't set up correctly .

Do the spark first . It should throw a good strong 3/8 to 1/2" long blue spark from the coil HT lead to ground as you open/close the points...... if it isn't then something is wrong with your coil circuit.

The leads need to be good , use a multimeter to check for continuity .... those horrible LUCAS screw in connectors in the dissy cap are woeful.

I bought an expensive aftermarket LUCAS repro coil and it was absolute junk..useless, made in India or somewhere . The car backfired and jumped about missing . I used the original 60 year old one ..works fine .

Mike

[Scallops]

Thanks Mike - I'll be going through all those things in turn. According to Dave, my carby is blocked - didn't make sense to me, since it drove near fine the day before, but he is a knowledgable fellow, so off the carby has come again. I'm getting good at this now!

I'll now do what all the info on planet earth says don't do and take it all apart to shoot carboy cleaner through it all. :eek: Think I'll have a camera and notebook ready for this phase.

Then at least once its all clean the problem has to be elsewhere.

To my original question - the manual says 10 degrees BTDC for timing - but this is for 80 octane fuel. I run 98 - should this be advanced to 15 or 20 degrees?

[wrinklearthur]

Then at least once its all clean the problem has to be elsewhere.

To my original question - the manual says 10 degrees BTDC for timing - but this is for 80 octane fuel. I run 98 - should this be advanced to 15 or 20 degrees?

Hi Scallops

I stand to be corrected as the saying goes, but have a read of this.

Is High Octane Gas Worth the Money? | Wanderings (http://www.wanderings.net/notebook/Main/IsHighOctaneGasWorthTheMoney)


" High Octane - Simple Definition
Technically, an octane rating measures the proportion of isooctane to heptane in a fuel. But as a practical matter, a fuel's octane rating relates to how much energy it takes to ignite that fuel.
The higher the octane number, the more energy it takes to ignite the petrol."

This has reminded me of another thing that does cause back fire , that is the coil can break down under load, try another 12 Volt coil in it before you change any thing else.

Coils for early, Holdens, Falcons etc are not 12 Volt as they have a resistance built into the wiring feeding the coil, from memory those coils are rated at about 7 Volts.

You need the one like they use in a 12 Volt Fergy tractor.

Such as this one on ebay

https://www.aulro.com/afvb/images/imported/2011/09/473.jpg (http://www.ebay.com.au/itm/Ignition-Coil-Massey-Ferguson-TEA20-35-135-Tractor-5977-/390341665721?pt=AU_HeavyMachineryParts&hash=item5ae22d23b9)Ignition Coil Massey Ferguson TEA20 35 135 Tractor 5977 (http://www.ebay.com.au/itm/Ignition-Coil-Massey-Ferguson-TEA20-35-135-Tractor-5977-/390341665721?pt=AU_HeavyMachineryParts&hash=item5ae22d23b9)

Item: 390341665721

Store: Wagga Tractor a... (http://stores.ebay.com.au/Wagga-Tractor-and-Truck-Parts)


Cheers Arthur

[Scallops]

Hey Arthur - I'm running 98 octane after a thread I put up here ages ago recommended premium as it has less additive that causes degradation of diaphragms/rubber parts etc.

It was the 100% consensus then! :)

[series1buff]

I'm no authority on this but I believe that higher octane modern petrol burns or combusts slowly compared to the lower grade stuff of years ago . Because of that , you advance the timing so you can account for the longer burn .

Oh BTW .............that's the crap coil I bought, a tractor one for a fergy . Not impressed at all. You can buy new non-resistor BOSCH coils .... I would be going that way rather than a garbage thing made in a sweat shop in a 3rd world country.

Mike

[wrinklearthur]

I'm no authority on this but I believe that higher octane modern petrol burns or combusts slowly compared to the lower grade stuff of years ago . Because of that , you advance the timing so you can account for the longer burn .

Oh BTW .............that's the crap coil I bought, a tractor one for a fergy . Not impressed at all. You can buy new non-resistor BOSCH coils .... I would be going that way rather than a garbage thing made in a sweat shop in a 3rd world country.

Mike

Hi Mike

Sorry to hear about that tractor coil not working for you, did you send it back to whom you purchased it from and what was their response?

With those, early side and overhead valve motors, is it wise to use a high octane fuel, as they are well known for burning their exhaust valves ?

Ok, then the timing should be advanced for the higher octane fuels, as the burn rate is slower and more consistent. When running the motor on power Kerosine where is the timing best set then?

Cheers Arthur

[series1buff]

Hmmm , not sure about timing and power kero .We need some vintage tractor people to answer that one . But during and after WW2 when petrol rationing was in force, some people ran their cars on kero. It was illegal as kero wasn't taxed . You made up a device to heat up the inlet manifold so the kero would atomise to some degree .

I think the burning of exhaust valves is from running a lean mixture ..... this results in a longer burn , but maybe for different reasons .

this is interesting http://motorcycleriderz.motionsforum.com/t196-octane-is-not-how-fast-a-fuel-burns