Strobe timing at tickover or high revs

[B Faiers]

I saved a document from the web called:- lucas_distributor_specs_pdf I can't remember where it came from. Possibly the Distributor Doctor.

This is what it says about the 41288

Service Number:41288A. Model 25D4. Rotation CCW.
RPM 1 1500, Advance1 10 + or- 1degree .
RPM 2 800 Advance2 9 + or- 1degree.
RPM 3 300 Advance3 3 + or- 1degree.
No advance below 200
Vacuum code 5/13/10 (y) Push fit
Years fitted1966-70 MG Model MGB 18V581F,18V582F,18V583F,18V581Y,18V582Y,18V583Y (HC)

For my two pennyworth I would get an original distributor overhauled by The Distributor Doctor. When electronic ignitions fail they fail completely and you are stuck, at least with points you (or the roadside recovery) can fiddle and adjust and get going again, if you keep points properly set up they are no problem.

[Ian F]

Thanks for that info. Barry, interesting! I wonder if those figures indicate that the Bob weights move at very low rpm? I was surprised to see a difference in advance between 200 and 300 rpm?
As an aside, my 1972 MGBGT has an engine with an 18V 582F number, original I am certain, so a little discrepancy in the data.
I agree with your advice on getting the DD to rebuild an original distributor.

Ian F

[Bumpa]

I don't really understand the engine nomenclature in the data that B Faiers has posted. According to Clausager in "Original MGB" the 18V engines weren't introduced until August 1971, with chassis number 258001. Is that table showing that cars up to 1970 had 18V engines, or am I misreading it? My 1971 car, number 253272, has an 18GG engine.

[Ian F]

Mike,. I think you are correct here - at least some of that data is inaccurate? Unless Barry made a typo in transcribing it, it does cast some doubt on the data source.
Would be very good to follow it up and get things clarified.

Ian F

[B Faiers]

I have found the original chart on the MGA Guru website: https://www.mgaguru.com/ go to 'Tech' and look for article IG126P
I have checked the chart and there are no typos.
I have just seen the info at the bottom of each page which is:-
www.starchak.ca www.TDCperformance.ca Copyright 2006 TDC Engineering

I have also looked at the Distributor Doctor website and the chart is not on there.

PS The MGA Guru website is an absolute mine of information - particularly as the early MGBs have much in common with the MGA

[Ian F]

Thanks for all of this Barry, much obliged. I will take a look and see if I can make sense of it. I did dig out the advance curve for my 25D4 as rebuilt by the Distributor Doctor, unfortunately it's not straightforward to interpret! I will take a scan or photo and if legible I will post it here and see what anyone can make of it.
Thanks again
Ian F

[B Faiers]

I went to a John Twist workshop at MGOC about 5 years ago, and I did make some notes on how he set up the 'B' . I'll see if I can find the notes. From memory he was setting things up very advanced, and recommended a tickover of 1000 rpm (I use 750 and if I remember the book says 600).

If you look at https://universitymotorsltd.com/ there should be some guidance.

[Paul Hollingworth]

If your 18V engine has the 25D4 distributor then it should also have HS4 carbs. These have separate float chambers and the vacuum advance take off from the throttle body of one of the carbs. (not from the intake manifold) If this is the case then 41288 is the correct advance curve according to Paul Hunts website. The strobe timing I would go for would be 19 deg BTDC at 900 rpm vacuum disconnected. I'm not sure but I think your engine also benefits from a big valve head.
I think you have to add the 10 deg static advance to Barry's numbers. I also have a 71 with 18GG engine and my advance curve is 40897. This is the same as most of MGB production up to this point. I did some research into advance curves when we were setting up my friends 123 electronic distributor and there was very little difference between 40897 which was curve number 2 and 41288 which was curve number 6 in its memory. I'm convinced the engine wouldn't know the difference. It was the thickness of a line when you plotted them out.
The Haynes manual concurs that the strobe timing is 13 deg BTDC at 600 rpm for the early 18V

[Michael Barclay]

Hi Geoff
If your engine is an 18V582 then hopefully the attached might help. The 18V581/2/3 series engines were in production cars from 72 to 73. They were fitted with the sort- after big valve head. In late 73 (November time) the engines were changed to the 18V846/7 engine with the introduction of HIF carbs and the 45d distributor. The engines are all painted black.
I suspect the “spare “distributor (41288) that came with the car is the original one for your engine. They are prone to seizing up if not regularly lubricated. Check the shaft the rotor arm sits on moves and the bob weights are not seized on their pivot’s. Fitting one of the readily available electronic modules in place of the points will help compensate for any play in the distributor and eliminate dwell angle settings. The attached info gives the advance curve info for centrifugal and vacuum so you should be able to check the operation of the distributor using a strobe light. Your engine started life painted black. Hope this helps.
Best regards
Mike Barclay

[GeoffK]

Dear All. My Mastermind Specialist Subject is MGB distributors !! The missing link is knowing exactly which engine is fitted to my car. The log book suggests 18v582 and the old distributor is 41288 but with no number plate on the engine I can’t be sure. I have the manual that Mike has posted the relevant page so I think my safest bet is to try 13 btdc @ 600rpm. Thanks for all your input-who knew there was so much science in these old beauties. Geoff