Ignition timing

[david c]

Sorry folks, another probably daft question.

I tried improving the ignition timing on my '67 4A this afternoon with mixed results.

Checking with a timing light I found the little hole on the crank was approx. one inch to the right of the pointer. Is that a lot? the car runs fine albeit with a little over run on switch off.

I turned the distributer to get the pointer and the hole to line up but set like that the engine won't run........at all. in the end I managed to get the engine to run nicely with no over run with the hole / pointer only half an inch out. Mind you not road tested yet.

How can setting the timing marks "right" result in a non running engine?

Glad of all and any advise David

[Lebro]

The 1" to the right is approx correct. 

10 degs BTDC is a good starting point. If you line up the hole with the pointer that is 0 degs BTDC,& is way too retarded. Also the vacuum advance pipe should be disconnected when checking this.

Bob

[david c]

Thank you for your reply and advise

Took the little beast out for a run today, cos your supposed to, drove really badly the car not the driver! still it was nice to get out even if it did take what seemed like an age for the engine to finally stop.

So as the performance was really poor I decided to go back to basics and start from fresh with the static timing, what a difference! it pulls like a train................still got 'orrible run on though,but that's another story. current theory is  a bit too much retarded  (once again the car and not the driver....probably, and bl**dy E10 fuel put in a couple of gallons by mistake.

 

Thanks again Lebro

[ctc77965o]

Factory ignition timing was defined based on the fuel quality of the 1960's and fresh mechanical components... Whats important is the timing at wide-open-throttle at real driving speeds, taking into account the actual fuel used and the wear in ignition & other components....ignition timing static or at idle is not particularly important to the drivability of the car.  The simple technique of setting ignition using the distributor thumbwheel to advance ignition & explore the point where pre-ignition starts on warm engine, flat road, 30mph direct 4th gear, WOT. The best ignition timing is a setting where timing is as advanced as possible without pre-ignition under these conditions. That takes into-account the fuel quality and the scatter of ignition due to wear & tear.   

[Andy Moltu]

Run on is just one of those things. Usualy stops after a second or two.

With carbs the fuel continues to be delivered and if there is anything sufficiently hot to ignite the fuel air mix it will run on.

In theory the timing doesn't matter as there should be no spark when the ignition is turned off, but if the engine is running hot and the tips of the spark plugs or other area get hot enough to igniite the fuel air mix it might just be a factor.

Later cars on SUs had anti run-on valves to inhibit run on.

[stuart]

1 hour ago, Andy Moltu said:

Run on is just one of those things. Usualy stops after a second or two.

With carbs the fuel continues to be delivered and if there is anything sufficiently hot to ignite the fuel air mix it will run on.

In theory the timing doesn't matter as there should be no spark when the ignition is turned off, but if the engine is running hot and the tips of the spark plugs or other area get hot enough to igniite the fuel air mix it might just be a factor.

Later cars on SUs had anti run-on valves to inhibit run on.

Timing and tuning certainly do make a difference to run on, modern fuels dont help but it can be eliminated.

Stuart.

[Andy Moltu]

The ignition timing can only influence running on if it cuases the engine to run hot enough for something in the combustion chamber to ignite the fuel air mixture, be that a hot spot or compression ignition to occur once the spark has gone.

Ultimately once the ignition circuit is turned off there is no spark and thus no timing, after all what we refer to as ignition timing is the timing of the spark relative to crank position and if there is no spark...

However there is the theoretical possibility of induced current from an electric fan keeping the ignition circuit energised in which case a weak spark might occur and provoke running on if timed correctly.

 

 

[david c]

Thank you Gents.............if I'm still allowed to use that term.

From your joint input I have to conclude that in all probability I'm going to have to live with it to some extent, a shame it's a little bit embarrassing when you pull up in your shiny little classic.........and sit there for what seems like an age (probably no more than 5 seconds) with your pride and joy spluttering away.

I will continue to try adjusting the thumb wheel on the distributer to see if I can improve the situation, without loosing my new found performance. I will also try using a fuel additive, and diluting the nasty E10 with the best petrol I can find. I will also look at improving the cooling as it seems the hotter the engine (the longer the run) the less the engine wants to stop.

I know many people suggest a build up of carbon in the cylinder head and on the pistons, my engine has only done about 500 miles since a full rebuild so that potential problem can go to the back of the queue..............I hope.

Thanks Folks

 

[rcreweread]

David - try and find and use Esso premium which typically in our part of the country has no ethanol in it despite the pump saying 5%. Other "good" petrol is Shell Optimax or BP Ultimate.

As for the running on, when you come to switch off, put your foot on the brake and with it in gear, clutch down, let the clutch up as you switch the engine off and effectively stall the engine straight away - with a little bit of practice, you can do it so well people will not even notice! Bring the car along to the Alma on Thursday and I'll show you!

Cheers Rich

 

[Ralph Whitaker]

16 hours ago, Andy Moltu said:

However there is the theoretical possibility of induced current from an electric fan keeping the ignition circuit energised in which case a weak spark might occur and provoke running on if timed correctly.

 

 

This was the cause of the running on on my car, if the fan was running at switch off the car kept going. Cured by fitting a relay activated by the temperature switch and powered from the ignition, or switched, side of the fuse box.

Running on could also be a sign of the car needing a de-coke.

Could be worth trying a cooler running spark plug first.

Ralph

[Ralph Whitaker]

Sorry, just read that the car was apart 500 miles ago, so forget the de-coke part. I think I would be putting in some different spark plugs as it is most likely that the tips are acting as glow plugs. That could be due to a weak mixture or incorrect ( advanced) ignition timing.

Ralph

Edited April 26, 2022 by Ralph Whitaker

[keith1948]

Hello David

Had a problem with my 4A running on a few years ago now. I changed to a cooler spark plug so instead of NGK BP6HS I went to BP7HS (fast road plug). Problem solved. I figured that the hotter plug was glowing and igniting the fuel after the ignition was switched off. I did think of fitting one of those automatic anti run on valves  but although I have the bits I didn't need to.

Too lean a mixture will also not help. Look at your existing plugs. If they are black its too rich, white too lean and brown just right.

Keith

[david c]

Thanks Ralf and Keith

The plugs, that's an interesting point, at the moment i'm running those NGK multi point plugs, I will change them tomorrow and see what happens.

I did pull the plugs yesterday to check the colour and they were a healthy brown colour, but for the sake of a few quid I'll try The cooler plugs as suggested.

See you Thursday Richard

[r-fox]

Hi from Austria,

with interest followed your discussion.

Here  thoughts coming out of my experience with my classics a TR4 1963 and a Volvo 123GT  1967.

Both have got welltuned homebrewed engines, TR 150, Volvo 180 bhp .

@ running on, may also derive from sharp edges (i.e.hot spots) arround the combustion chamber remained after having  flattend  the cyl.head. .These should be radiused by abt. 2-3 mm , same to edges arround the plug hole. . I'm sure you 're familiar with.

@ ignition timing , I'm used to adjust with timing light at 21 to 23 ° at 1500 revs both cases.

@ plugs , Changed for quite a while from NGK  BP7HS  to Iridium type   NGK  BPR7HIX  both engines .Excellent decision !

@ plug's colour , rather light-grey than flawn with today's fuels specifically austrian.

Some words to the fuel situetion here in Austria :

     Thanks Goodness NO E10 in Austria . Run 98 octane  (Super +) which is in this part of the world on a MAX  E5-basis if any ethanol

     content .

     There are also brands having 102 oct. (Shell) also on E5. On vacation trips to Italy I take an additive octanebooster   "104+" ( US made)

      with me pushing a 95 ( E5 ) up to 100 octane.

      That should not change acc.to the austrian authorities in regard of the supply of classic cars  !  Nice isn't it.

 

Wolfgang