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Distributor vacuum unit


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Hi all

I’m about to embark on a 200 mile drive tomorrow and I noticed that the vacuum tube connecting the distributor vacuum unit to the carb is broken. It is half broken by the nut that connects it to the vacuum unit.

The car has been running fine. I’ve covered 300 miles since the weekend on my trip and this doesn’t seem to be affecting the engine, so I guess the question is do I need to worry about it breaking off? I’m thinking that I should wrap it with some tape for now and then replace when I get home. What effect does this actually have on the engine? Maybe I loosen the nut and feed more tube in?

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Dan

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1 minute ago, DanB said:

loosen the nut and feed more tube in?

 

If there's enough slack. Otherwise I'd just plug the tube and leave it until you can fit a replacement - it doesn't make a lot of difference in gentle road driving.

Pete

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More often than not, the diaphragm has seized and the whole mechanism isn’t functionning - maybe for several years!!. I did away with mine some twenty years ago.

Make sure you plug the manifold side if you decide put off repairs until later.

james

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9 minutes ago, stillp said:

 it doesn't make a lot of difference in gentle road driving.

Pete

The ONLY time it makes a difference is in cruising where the throttle is only partially open. It does next to nothing when you are pressing on. The idea is to advance the timing during cruise to get better mileage. 

I think you may find there is a metal olive on the end of the tube. That squashes down onto the tube to make a seal so you may not be able to feed any slack through. As James says, if you leave it you need to plug the carb end of the tube else the air drawn in will be weakening the mixture. 

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An expert will be along any minute and correct me if I'm wrong but I think it works like this, 

The advance weights open to give more advance at higher revs for economy and performance modulated by the two small springs and the vacuum unit retards  the ignition at low revs when engine is under load, like on a hill to prevent pinking. If a fairly standard engine runs ok without the vacuum unit then it must be set retarded to avoid pinking 

Chris

 

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The distributor weights and springs determine the basic advance at any given engine speed. The vacuum advance unit provides additional advance beyond that if the throttle is at a low opening.  The additional advance is lost when you open the throttle wide but it only reduces to that amount of advance set by the weights. It does not 'retard' below that.  The distributor position should be set without the vacuum pipe connected anyway, so losing the pipe does not require any adjustment of the timing.  

There are retard units which do what you say but those are mounted on the other side of the distributor. 

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You could take the nut off the vacuum unit and try and find a small piece of plastic tube that would fit over the thread, and go over the black tube, you may need to be a bit industrious to fit the black tube, but something like Patafix putty should do the job.

John

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16 minutes ago, John L said:

You could take the nut off the vacuum unit and try and find a small piece of plastic tube that would fit over the thread, and go over the black tube,

I've used a piece of heatshrink tubing in the past.

Pete

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Happy to say that my 200+ mile trip went without a hitch (closer to 250). In the end I tried to reinsert the remainder of the tube but I couldn’t get the olive on, so I just improvised with some insulating tape. This worked absolutely fine. The car ran like a dream. I’m a pretty new owner and had visions of the bonnet up at the side of the road, but the engine is incredibly strong and she was faultless!

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