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Guys...What is this on a HD8???

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AH_3000

AH_3000

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I know - probably an easy question, but the "thing" I've marked on the picture of my engine bay, is a small "pipe" from my aft HD8 carburettor. I've seen pictures of engine bays, where this is attached to a thin copper pipe, which ends...where??

I'm new at this, but I'm determined to learn...from you :smile:!! My 1967 Mk III runs pretty good, but there has to be a purpose for this thing...what? Should I connect it somewhere? Just been to the SU page but no answers there...

Best Regards

Chris

SWEDEN
 

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small pipe......off a vacuum source.....hard to tell by the photo, as my glasses seem to be suddenly out of focus, but the description must be vacuum advance line to the distributor, without looking.

Wish I could see it.
 
Hi Chris,

Good eye.
That's the vacuum advance adaptor. It connects via a rubber tube to a long copper tube (which from the factory was painted engine green). That copper tube travels around the back of the engine and connects to the vacuum unit on the distributor.

Roger
 
Thanks, guys!

TOC: In my ambition to show the detail clerly, I blurred the surrounding parts and made them B&W...from your post, I can understand that I didn't do a very good job :wink:!!

Roger: Nice pic's and an awesome detailing of your engine...!!
(probably one of the reasons that I blurred the picture of my engine...Not finished yet...)


The point is: My Healey is running like a clock, but without the tube to the distributor....what am I missing? Since it came with a tube from the factory, I guess it is important, but technical skills aren't that advanced (I'm just an airline pilot) but I relly would like to know what it does etc???

All the best,

Chris
Sweden
 
P.S. I've now learned(from a book) that the vaccum advances the ignition timing (small throttle opening - high vaccum - advanced timing, large throttle opening - low vaccum - ignition retarded).

Still - do I need it? The engine is running well, but I must confess, the running on idle could be better...

D.S.

Chris
 
Here is a picture of my distributor without the connection! Could it be a later type (it's a 1967 BJ8) without the need of vaccum to control it??
 

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Your distributor has a vacuum advance unit--it's the silver 'flying saucer-shaped' disk on the side. The part on the rear carburettor is the vacuum port or 'pickup.' If it's not sealed it would be an air/vacuum leak and could contribute to your idle issues.

The vacuum advance on a Healey SU carburettor is known as 'port vacuum'--it picks up the vacuum at or near the throttle plate (another type of advance is 'manifold,' where the vacuum port is located on the intake manifold). It will only advance the ignition at part throttle--i.e. at midrange cruising speed. There is no retard circuit. Some cars, maybe MGs or Triumphs have vacuum advance and retard circuits. Most (older) American cars have manifold vacuum advance.

The main consequence of no vacuum advance is mileage efficiency. A BJ8 in good tune will deliver up to 24mpg at 55mph cruise, around 19-20 if you're flogging it on the highway and around 15mph in 'city' traffic or on windy, steep grades (mountain roads). AFAIK, all Healeys had vacuum advance. Some cars--mostly 'race' cars--are modified to only use mechanical/centrifugal advance. Your engine looks very stock.

Unless you can determine that the distributor has been modified to only use/need mechanical advance, I would get this fixed.
 
The only real reason for no advance is if someone, somewhere decided to "lock" the vacuum advance internally.

My distributor (25D, if I recall), acted very oddly.
I discovered the advance was blown, ordered out a replacement, when I went to install it, found some MORON had removed the breaker plate and BRAZED the movable portion in place.
Mine has and external timing adjustment wheel, which then did not function.
I removed the plate, used a cutoff wheel on a Dremel, and cut the braze all out.

Works very well now, like it's supposed to.


I would guess end of the steel/copper tube is somewhere close to the vacuum advance.

Use your pre-flight walkaround experience to find it!

Dave (who is still trying to clean his glasses)
 
Thanks a bunch, guys!

I'll go ahead and fit a new pipe etc. and I'm expecting the fuel consumption to drop and the slow running to improve!!! I'll post the results here within 2 weeks - vacation in Spain delays the process... :frown:

Dave - I'll do the walkaround (nowdays, in Europe, I mostly check for dust and other particles from the infamous volcano at Iceland....Maybe that's the problem with your blurred glasses as well? Do a thorough spectacle walkaround... :wink:

Chris (who has perfect eyesight and doesn't need glasses...YET!)
 
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