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How to fix vacuum advance?

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100DashSix

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I had tested the vacuum advance on my distributer and found it didn't hold vacuum...I just kept inhaling, and nothing changed. I notice that Moss doesn't list the vacuum unit itself for sale (says it's included with a new distributer). Can repairs be made to the one I have? Is it worth it?
 
Think repairs not possible but saw one on ebay for a wild price, look for an old dizzy with a good vacuum advamce you can move over.
 
Also consider British Auto Electric in Anaheim, CA. I've had many components rebuilt by Jerry with great results. He's also a multiple MG owner.
 
/ubbthreads/images/graemlins/savewave.gif
--100-6:

Naw Jack, there are several rebuilders of the Vac Adv unit some, are listed on these forums.---Keoke- /ubbthreads/images/graemlins/yesnod.gif
 
Just for the record, You could also just leave it as is.
The real function of a vacuum advance on most of these cars is pretty subtle(* but see note below). It provides just a little bit of extra torque at moderate engine speeds in the higher gears (in other words, the engine will "lug" a bit better when you're going 20 mph in 4th gear).
It makes no real difference at idle and when you are driving in a "spirited" manner, it does not really make any difference either.
My guess is that most people would not even notice if the vacuum advance was disconnected.
One of the first things I did with my race car was to pull off the vacuum unit and throw it away.

Note: Some newer Brit-cars built around the early 80s used a "vacuum advance/retard" distributor for emissons purposes. These vacuum units need to be hooked up or the car will run terrible.
 
Oh really, think I missed that. Who? Do a good deed and help an old guy out, lol.
 
I'm a bit surprised Keoke's answer was so short. That's not meant as an insult... I just remember a similar thread on the Healey forum and I could have sworn it was Keoke who posted information on how to replace the diaphragm in the advance units. Keoke... if it wasn't you, was it Dave Russell?
 
I never thought about a vacuum advance contributing anything to power. I always understood that they kicked in a little extra advance at part throttle to improve fuel economy.
 
Nial wrote: [ QUOTE ]
Note: Some newer Brit-cars built around the early 80s used a "vacuum advance/retard" distributor for emissons purposes. These vacuum units need to be hooked up or the car will run terrible.

[/ QUOTE ]

I thought the '74's were fitted with the advance/retard units, but if it ran well without it I'm wrong. I'd look to making sure the mechanical advance is working and "deep six" the vacuum "thingie." My early cars all got springs/weights modified and the vacuum units were just left unconnected.
 
The ST (Special Tuning) distributors were made without vacuum advance altogether. If you run a side draft weber, for instance, there is no provision for VA anyway.
 
I left mine for the vernier adjustment knob/wheel thingie. /ubbthreads/images/graemlins/wink.gif
 
Thanks for the advice. It sounds like that, considering all of the other things I can do to the car, fixing the vacuum advance should be relatively low on the list.
 
Just disconnect the vacuum hose and block it off to keep the leaky diaphram from effecting the mixture. Mine has been disconnected for over twenty years. I don't miss it.
 
The oft-repeated "race cars don't have them so I don't need one" argument is a fallacious one. Carl Heideman put some telemetry gear on a race car and a street car and measured how they were driven. The race car spent about 95% or its time above 4000 rpm. The street car spent less than 2% of its time there. So, unless you drive at WOT, ALL THE TIME, what works on a race car is irrelevant to what you want on a street car. Vacuum advance gives you better fuel economy, better part-throttle drivability, and better temperature control. Fix it -- you'll like it! :smile:
 
I actually now plan on getting the dizzy rebuilt, and--if I may continue the thread in a new direction--I was wondering if the following problem I'm having may be attributed to an overall worn distributer (and the problem described I described in the thread about the car running poorly at low revs):

The idle is very rough. The engine was apparently professionaly rebuilt maybe 10 years ago now, but I think that this vacuum advance on the distributer didn't get any attention..along with the distributer itself, as it looks rather tired. The original SU carbs were also neglected during the rebuild. This all makes me think that my problem might be partly due to the overlooked distributer.

What I'd like to know is if I could expect better performance if the dizzy is rebuilt, with the mechanical advance refreshed and all that.

Anyone get a new/rebuilt distributer and find a lot of difference? Was rebuilding it worth the money?
 
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