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 Posted: 06-23-2024 12:43 pm
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fenflame
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I just bought a distributor from MR in the UK for a Stromberg equipped 1973 JH.
What arrived had me very confused, it is the correct fitment with the oil seal, even the mechanical advance is somewhat correct, however it has a vacuum advance capsule thats mounted on the opposite side of the body to a 41497. The direction arrow on the body is the opposite to the 41497 as well, though that aspect has always confused me because the 41497 shows the direction opposite to what the real direction is.
The part from MR is def a 25D4 that has been rebuilt, but who knows what model they started with, but it def looks like it wasn't a JH original part.

The vacuum advance adds around 5 deg of advance. No JH has had vacuum advance that I'm aware of. Not sure if to just disable the vacuum and call it a day given the mechanical advance is close enough. Rebuilding the original41497 is a possible option, but its in a pretty bad mess and was previously rebuilt by the PO and someone had put the wrong vac capsule in, so that one has vacuum advance as well, though extremely rough with lots of binding on the base plate. How is it even possible I end up with two dists with vacuum advance :)

https://www.martinrobey.com/jensen-healey/jensen-healey/jensen-healey/electrical/engine-electrical/12782

Cheers, Alan. 

Last edited on 06-23-2024 12:47 pm by fenflame

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 Posted: 06-23-2024 01:45 pm
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noomg
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fenflame,

Fifty years down the road a lot of exact replacements are getting scarce so using parts from other makes isn't uncommon it's what the Brit makers were doing when still in business. Aston-Martin used J/H taillights, Lotus used the same gas cap.

The J/H dizzy does have a vacuum advance just not in the same place as this replacement, it's just off to the side. It looks like this dizzy will work but I'd give Martin Robey a call to confirm that.

BTW, Stromberg didn't make distributors, it's a Lucas.

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 Posted: 06-23-2024 02:19 pm
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fenflame
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Thanks for the reply. Absolutely agree with you. We have to make do and mend a lot more now with more and more parts unavailable.
Some background as I'm new to this forum and its  impossible to know peoples skill level. I'm a 55 year old Brit Engineer living in the USA for the past 20 years. I've restored many British cars over the years. Ironically I own an Aston Martin Vantage too. Used to have a DB7, that had Mazda 323F tail lights !  This JH is the latest project. I've been at it for about a year, rebuilt the engine and transmission, steering, suspension and become very friendly with Mike at Delta in the process :)  It runs well, just trying to ties some loose ends up. The distributor does work fine as I just leave the vac disable.

Haha....I meant a Stromberg equipped JH as opposed to a Dellorto equipped. Yeah I know its a Lucas Dist ;)

Let me reword: The Lucas distributor on the Stromberg Carb equipped cars in the US has a vacuum retard, not an advance. This distributor has a vac advance, not something that ever existed on JH's (from all sources I can find).

My point of posting was simply because MR are one of the biggest sellers of JH parts and they are shipping out a distributor for Stromberg carb equipped cars with a vac advance capsule when from every piece of documentation available it should be a vacuum retard capsule. THats not to say it can't be made to work, but there is no baseline for vac advance for the 907 that I'm aware of.

I have emailed MR to see what their take is, it could be as simple as the wrong capsule has been fitted.

Last edited on 06-23-2024 02:32 pm by fenflame

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 Posted: 06-24-2024 05:16 am
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Tim Murphy
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As I understand, the vacuum retard was for emissions purpose only. So set it up with and without vac advance to see which gives the best, most accurate advance. Another note, the max total advance of 27 degrees BTDC is said to be tested as best.

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 Posted: 06-25-2024 11:59 pm
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vnavaret
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That particular vacuum capsule can be moved to the other side of the distributor if you wish. That would convert it to a vacuum retard. Unscrew the knurled nut, remove the dizzy cap, rotor, and breaker plate. You can unhook the vacuum capsule, and reinstall it on the opposite side of the dizzy, and reassemble. Voila, a vacuum retard.

Installing it with the advance increases your highway fuel economy by about 3-5%, which is why most cars use an advance. And yes, the retard is for emissions only.
If you do use it as an advance, you will need to connect the vacuum line to a vacuum port on the top of the ZS carb, you cannot use the port that was formerly used for the retard. Off hand, I don't remember if there is an advance port on the carbs or not.
Vance

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 Posted: 06-28-2024 02:59 pm
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redracer
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Alan: just saw this thread. Yes, it's a retard capsule, not an advance as you noted. Since they were for
pollution: as Tim pointed out, they usually go "bad" very quickly/ Since they are not need ed (unless you're located in some place that requires that) we just remove them totally and seal up both sides with whatever, usually silicone). You must also screw the to swivel plate to the bottom plate so you don't have the timing bouncing around. The #6X32 thd/in for the condenser provides a good place to do that.
Your total advance(around 3000 rom) should be no more than 30BTDC, unlike most older American cars with their same-side intake-exhaust manifolds being 35-37BTDC. Your idle timing will likely be around 15BTDC now, which is fine.

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