T-Series Wanted: Vacuum Advance Valve/Switch?

[Bret]

Hi Gents,

Best I can tell from the replies to my previous posts on the subject here in the MG forum and the Tools forum, most of you with the later Rubber Bumper MGBs (75-80), have already removed their old restrictive Zenith-Stromberg set-up.

With that said I would like to know if any of you still have your Vacuum Advance valve? This is the Vacuum switch between the intake manifold and the distributor. The switch only allows vacuum to advance the distributor when in 4 gear.

So if you still have this and are willing to part with it please let me know, as I am willing to purchase this item? Or if you know of another source feel free to let me know?

Thanks in advance (pun intended),

Bret

 

[DoubleDiamond]

Ok I'll bite, I have never heard of one of these valves, and why would you want to have vacume advance in 4 geer?

I have converted my 77 B and may still have this part some where.


Shawn

 

[tony barnhill]

Its the little black thing screwed to the back lip if the master cylinder housing cover.

 

[DoubleDiamond]

is it part of the break servo system? how does it connect or effect the distributor advance?

 

[tony barnhill]

electrical impulse tells it what the engine rpm is & it kicks up the vacuum to the distributor....but don't ask me what that means 'cause I don't understand electrical systems....

 

[DoubleDiamond]

Hmmmmm I will do some research. see if it is still there, or in the box of spares.

 

[piman]

Hello Bret,

I really can't understand the point of it?

On the more common vacuum advance mechanisms it responds solely to vacuum, basically throttle position. It rarely operates in the lower gears as you are accelerating.

If it does operate only in fourth gear it will need a switch on the gearbox to activate it.

Alec

 

[WA1KWA]

Sounds like Transmission Controlled Spark Advance. The following link may be of some help.

https://books.google.com/books?id=h2pqrXt...lbNDFR4HKymyC4E

Also here: https://www.british-cars.org.uk/kimber/namgbr/techtips.htm Look under Hoses-tubes-lines

Colin

 

[DoubleDiamond]

On most of the rubber bumper cars there is a antirun on valve. this valve is located on the front lip of the washer bottle holder and connects to the carbon casister and creats a vacume in the float chamber when the engine turned off thus preventing fuel from being drawn up the jet into the carb. Are we talking about this valve?

 

[tony barnhill]

No, its the TCSA he's talking about.

 

[DoubleDiamond]

Here is a site I just found that might help.

https://www.mgexperience.net/archive/correct_timing_vacuum_advance_questions/32387

I solved this problem with a 123\MG-4-R-V distributor. it has 17 programable curves.

https://www.123ignition.nl/brand/MG.html

 

[JeffS]

The valve in question uses manifold vacuum but doesn't allow a vacuum signal at idle, only while cruising in 3rd and 4th gears. You can eliminate the valve if you purchse a vacuum advance from a 1975 MGB. It should have the 10-15-5 specs stamped into it. That unit will give better throttle response, a better idle, and most likely better fuel mileage than the original, even with the TCSA installed.
Be careful though. Mnay of the replacement vacuum advances are incorrect for their intended applications, with a lot of them being 5-13-10 spec. Those are only good for ported vacuum SU applications!