16 replies to this topic

[DTXDave]

On my way to an important meeting I lost all power in the Mini. I limped to a pull-in place where I could take a look under the bonnet to see what the problem was. Turned out to be a split rubber connector on the distributor end of the vacuum advance pipe.

Got to my meeting by taping up the connector with electricians tape. Replacement part was pocket change from a local motor factors, so not too bad and quick and easy to repair. Started me thinking though about how important that little plastic pipe is on a Mini engine.

Had a quick Google for "vacuum advance distributors" and did some light reading. Well it's good to learn something new everyday, especially after a breakdown!

I wrote about the repair plus what I learned on my Mini project site - Linky , but I'm interested to know if anyone else on here has had similar problems and whether they have found ways of preventing this from happening in future, or if they keep a spare with them at all times?

I presume all Mini's with an A-series have these pipes, standard or modified?


DTXDave

[mars red mike]

I have had that silly little elbow on the vacuum unit of the dizzy split before and the car ran a bit rough but didnt lose all power.

[Ouster]

I would have thought it wouldn't bring a mini to a standstill, it would just drive a bit nastily at part throttle.

[DTXDave]

Interesting. Well I certainly lost pretty much all power. I could do 10mph, but as soon as I tried to go faster there was nothing and a sudden loss of what momentum I had.

Everything else seems ok, dashpot oil, carb, exhaust, air filter etc.

The articles I read online talked about how vacuum advance timing is used at low to medium power and is aimed at making the car more drivable and fuel economical, which would indicate that mechanical timing alone should work to some degree, but this didn't appear to be working for me. Could my timing be out perhaps? I do get run on for 1-2 seconds after a really long drive at 60-70mph.


DTXDave

[minimender]

I would say that your timing needs checking. It sounds like it is a bit retarded, this would cause the run on after switching off and when the vac pipe broke then you lost the bit of advance that was keeping you going.

Wouldn't do any harm to mark the dizzy and block with tipex so as you know where you started from and then twist the dizzy clockwise a bit, if the tickover speeds up then you are on the right track. Get the fastest tickover you can then slow it down on the carb adjuster.
If it dont pink then you've sorted it.

[icklemini]

Was showing a chap the other day what occurs to the timing and the Air/Fuel mixture when the pipe is disconnected and sucks in air...

Obviously the vacuum isnt acting on the dizzy so at idle so this drops the advance... but also it took the Co% down from 3.5 to 0.5 (uber lean!)

[bmcecosse]

Vacuum advance DOES work on the dizzy at idle! Pulls it up as soon as the engine fires up, thus allowing very little static advance setting for easy starting.

[Sprocket]

Vacuum advance DOES work on the dizzy at idle!

not when the pipe has fallen off, or the elbow has split

[Boycie]

The only thing I notice when the pipe comes off/ elbow splits is a slight hissing!

On my HS4, the pipe doesn't have any effect at idle, because the throttle disc covers/ closes the hole when the throttle is resting on it's stop. As I understand it, it's main function is at light throttle (high vacuum and the hole is uncovered!)

[minimender]

The only thing I notice when the pipe comes off/ elbow splits is a slight hissing!

On my HS4, the pipe doesn't have any effect at idle, because the throttle disc covers/ closes the hole when the throttle is resting on it's stop. As I understand it, it's main function is at light throttle (high vacuum and the hole is uncovered!)

I would check that the vac advance is actually working.

[lrostoke]

The only thing I notice when the pipe comes off/ elbow splits is a slight hissing!

On my HS4, the pipe doesn't have any effect at idle, because the throttle disc covers/ closes the hole when the throttle is resting on it's stop. As I understand it, it's main function is at light throttle (high vacuum and the hole is uncovered!)

This was mentioned in a previous topic I've got a couple of HS4 carbs lieing about so at the time I checked, the vac hole is not covered by the throttle disc at idle.



Also on mine I know the timing definitly changes at tickover with the vac connected or disconnected.

[zef]

The only thing I notice when the pipe comes off/ elbow splits is a slight hissing!

On my HS4, the pipe doesn't have any effect at idle, because the throttle disc covers/ closes the hole when the throttle is resting on it's stop. As I understand it, it's main function is at light throttle (high vacuum and the hole is uncovered!)

This was mentioned in a previous topic I've got a couple of HS4 carbs lieing about so at the time I checked, the vac hole is not covered by the throttle disc at idle.



Also on mine I know the timing definitly changes at tickover with the vac connected or disconnected.

Which is why you should do your ignition timing with the pipe disconnected.

[daemonchild]

It depends on the carb doesn't it?
I've seen some where the hole is on one side of the disc and others where it's on the other.
(If you see what I mean?)

So it would be in effect on only SOME of those carbs at idle.

[Boycie]

This has been messing me up for ages!!!!

Both the HS4 carbs I have here have the hole in line with the throttle disc, which covers it at idle.
And if I then suck on the adv/ret tube, my idle improves and smooths out..
So I have no idea why they are in different places or different HS4's.

Both mine are early pre-waxstat ones though.

[GraemeC]

There are different ways to source the vacuum - from memory they are called 'ported vacuum' and 'manifold vacuum' and they are taken from different places in relation to the throttle disc. Distributors (or more exaclty vacuum advance units) are specific to the type of vacuum drawn which is another reason that distributors should be matched to engine.

It is possible (in fact both of my last two builds) to pull so much advance from the vacuum at idle that it is difficult to get the car to run properly.