Ignition Timing

[sorbs]

Interesting. I tried three 25D distrubutor vacuum units and couldn't operate the vacuum advance by sucking on the pipe on any of them.

One was on my own car, one was on Resto's and the third was just the vacuum unit on its own which I purchased from CW.

They all operated easily enough by hand and the baseplates on the cars weren't seized either but as I say, several of us tried to operate them by sucking on the pipe and got nowhere. Perhaps they were all excessively sticky in operation, even the CW replacement? Maybe we all just need to get a decent set of lungs?

Given that the CW replacement vacuum unit seemed just like the one on my car, I didn't bother replacing it. I initially suspected the vacuum unit could be causing poor idling but having traced that problem to the breather valve diaphragm I'm going to leave the vacuum unit well alone!

[Umquat]

I remember on my old Beetle that I could operate the advance unit by sucking, but not a cat in hells chance with the one on the Triumph.. Either the one in the beetle offered a lot less resistance or I'm out of shape!!

Regards

Gavin

[Alec]

Hello all,

vacuum units have different specifications depending on application, they may look similar but they are not in effect.

Again, I suppose you could check them with a strobe but you would also need a vacuum gauge to compare vacuum with advance? I have never actually tried it, seeing as my distributor has no vacuum advance.

Alec

[Umquat]

Trying to remember... is your car fitted with a 123 unit Alec?

Regards

Gavin

[sorbs]

Trying to remember... is your car fitted with a 123 unit Alec?

Regards

Gavin

I rather suspect that Alec's car doesn't have a 123 unit fitted......

I'd like to see the advance curve for the 2000 vacuum system to find out exactly when it's supposed to operate. I suspect it's only at times of very high vacuum, perhaps on the over-run and that it may not have very much effect at idle? I'm not sure and am no expert on the subject. Either way, the spring resistance on all three units I tried was way beyond my asthmatic gnat sucking efforts.

As an aside, I once had to install and commission a vacuum distillation unit at work which was used to remove heavy oils from kerosene. It allowed the kerosene to be re-used. All I could really do was ensure that it operated within its design parameters and that the vacuum readings, measured in torr, were correct. Trying to equate the vacuum measurements to something meaningful like PSI left me rather confused.

[Umquat]

Now what are you saying about Alec's car!!

I'd forgotten just how nice mine looked two years ago... I think I might have to do a bit of a Chatterton at the weekend, although Its gonna take more than just polish and elbow grease to get it looking like this again!!

Have to say, that was a glorious day!! Beautiful weather, spitfire display, and the heady smell of racing fuel - made you queasy and your eyes water, but it was worth it for all the exotic machinery

Regards

Gavin

[Alec]

Hello Sorbs,

"I rather suspect that Alec's car doesn't have a 123 unit fitted...... "

Er, yes you are right!

If you let me know what year or better still what distributor (spec number) you have my manual gives the specification, as I said they do vary.

Alec

[Mike Stevens]

Alec beat me to it! The manual (pukka Triumph one) lists the centifugal and vacuum figures. They are only in table form , but you could plot the curve if you wished.

I tried sucking on the PI distributor I have on the bench. OK, it's not got a baseplate in it, but the little connecting mechanism moved OK. I'll get out my vacuum meter (or something suitable) and see at what pressure difference I can get it to move. OK, not very scientific I accept, but 'within an order of magnitude'!

Not now though. It's far too late (or too early!)

Cheers,
Mike.

[CAR]

I can get mine to move by sucking on the advance retard, and I could years ago on both of my 1850 Dolomites!

Cheers Colin.

[kevinw]

Interesting - if I disconnect the vacuum pipe at the carb and suck for all I'm worth (for example like attempting to "drink" a MacDonalds milkshake), I cannot get the baseplate to move. If I take the pipe off and replace with a wider bore pipe, with a reasonable amount of suck, the baseplate advances.. So then checked out the proper pipe - nothing wrong with it - it holds vacuum amd pressure, although tested with nothing more sophisticated than a finger over the open end.

Also had a look through the manuel and found the spec on advance against vacuum. As I've spent the day down at the bus museum, I thought I'd borrow a vacuum gauge to see how much vacuum there is at idle (very little, as Mike suggests, by feeling it). Can't find a spare vacuum guage, so gave up on that one. Did manage to swap batteries on 2 vehicles and convert one from 4 x 6v batteries to 2x 12v ones and get a Leyland Atlantean (11.25 litre 6 cyl diesel) to start and run for the first time in over 2 years. Just needed the fuel system bleeding - bit like a PI, only slightly larger scale.

Kevin