Using a snap-on timing light

[jb]

I have used a mt2261a snap-on timing light for years to confirm the timing to be 5degrees ATDC.
This is straightforward.
However I am trying to understand how I confirm the actual timing at 2000,3000,4000rpm etc.
I use the tach/advance button to confirm the rpm to be 2000,3000 etc then the increase advance button until the flash lines up with the tdc mark.
Is this correct?
Should I factor in that the 0 setting was on the ATDC mark?

[Nine One One]

https://www.theminiforum.co.uk/forums/t ... ing-light/

This any help?

[Jonny Hart]

It's basically a delay in flashing the bulb so that the timing you require shows on the tdc mark.

If you have the timing light adv set to 5 ATDC then you'd turn the distributor until the flash is on TDC (at idle).

If you wanted -say- 25 BTDC at 4000, set the light adv to 25 BTDC then you'd turn the distributor until the flash is on TDC when the engine is at 4000 RPM.

Since these lights have a microprocessor sampling/averaging the RPM, they are prone to jitter (light wanders about) so try to keep the RPM constant when confirming the timing.

[jb]

Thanks but sorry I still do not understand.
I do not want to turn the distributor at all as I want to determine what is the current advance curve.
The timing at 950rpm is set to 5atdc which I confirm by having no advance set on the timing light and the flash is on the 5atdc mark.
If I now increase the rpm to say 2000 as shown on the timing light display I can increase the advance setting on the timing light until the flash is on TDC and read off the advance but this right?
If I was to use the CDI+ to map out the curve I would like to have an idea of what it is currently first.
Thank you for your help.

[Jonny Hart]

Yes, that's correct. Essentially you're doing the same thing but the other way around - adjusting the lamp delay instead of the distributor position.

So, in your idle example, if you set the timing light to 5ATDC, the flash should appear on the TDC mark.

At 2000 RPM, you can adjust the timing light advance knob to get the light to flash on the TDC mark and that's your advance reading.

[Bruce M]

Yes, set the strobe to the expected advance at say, 2k then Rev to that and you will see if the flash is early or late. Then tweak the strobe setting until you get to actual figure which matches up with TDC.
That will give you the absolute advance and if you want the relative advance deduct the static advance.

[jb]

Thank you for your help
I was just trying to confirm that I had it right as mine seems well outside what I would expect
There is a massive jump from about 1500/1800 to 2000 where it went from 15 to 25 then to 32 by 2200


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[Jonny Hart]

Provided your readings are accurate, that would suggest the springs are weak in the distributor.

[jb]

Rebuild the distributor or use your magic on my cdi+
It is an early model cdi+ and a pre sc distributor so perhaps not so easy

[Jonny Hart]

well since you'll be in the distributor anyway, why not lock the weights and give it a go? We can put the map in it for you if you like.

[jb]

That sounds like a good plan.
Let me know what I need to do to lock the distributor as it is pre SC and I will then get the CDI+ to you to put on a map.

[Jonny Hart]

See here: https://classic-retrofit.com/forum/inde ... omment-178

[jb]

Thanks
I have not yet seriously looked at the distributor but it may be rubber ducked in more ways than just the springs so I was thinking that it might be a good idea to get it rebuilt first. Any recommendations for someone to rebuild it?
I will take the cap off and see if there is any obvious sloppyness first.

[neilbardsley]

I would put a tiny bit of grease on the shaft that opens/closes the points and a couple of drops of oil on mechanism. That might help.

As for someone to rebuild it. The chap I used is in the states. Hopefully someone will come along with a suggestion. They certainly need a testing machine

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[jb]

I took off the cap and wiggled the rotor and the advance mechanism.
There is some up and down movement and a bit of side to side movement in the shaft.
However I think the advance mechanism was getting stuck and then releasing as having manipulated it all I got different advance readings particularly at 2000rpm where is was 24 before but now about 18 and at 2500 where it was 32 and is now 21.
As this is not consistent it would seem wise to rebuild it.

I have looked at the various distributor rebuild threads on Pelican which are mainly for later cars and although I think I could probably do it, I would much rather get someone else more competent to do a rebuild.

Surely someone in the UK must rebuild them.
Our cars are mostly at least 40 years old so they all probably ought to have had the distributor serviced by now.

Even forty years ago I remember complaining to Charles Ivey that after they had serviced my 911E that I could not longer get 140mph out of it and they then replaced the distributor and the car was less than 10 years old then.