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MG Midget and Sprite Technical - Test Vacuum on Distributor

Hi Guys
Doing some routine maintenance and thought about time to clean & service the dissy. (Mk1 Frog Lucas DM2PH4). A question I can't find in the archives.
Is testing the vacuum mechanismm the same as on a later 25D4 , e.g. can you suck on the vacuum pipe and expect to see the plate move inside the dissy ?
I've done this and no visible movement but cannot suck any air through which suggests the diaphram is OK. Or do you need super human lungs to get it to move?
Obviously if anyone can shed any light on different/correct method to test the vacuum advance in the dissy it would be much appreciated.
thanks

Ed
Ed H

I used a little mitty vac on mine...its a little hand pumper... As to what pressure...i cant say, i just pumped it untill the vac advance plate moved

Im guessing your not gay ither.... ;)

Prop
Prop and the Blackhole Midget

Prop
If I am does that help the car run better?
I could always ask the wife to help but I think I know the answer......
Ed
Ed H

Despite being gay, I've never been able to suck hard enough to make the distributor move much. A tiny twitch is all it will do with lung vacuum- but you should be able to pull a vacuum and hold it on your tongue, if the vacuum leaks away then you have a split diaphragm.

For a full test you need a mity-vac tester.
Growler

hey growler

No offence was intended, i was just going for a cheap laugh...frankly i could care less what people do to help shot there goo...in the end we are all just.people trying to leave a good lookin corps behind and some great memories for our friends and family, and with any luck hopefully make the world a better place then when we came screaming into it

Your being gay is a non issue to me and im sure to anyone else on the bbs

Prop
Prop and the Blackhole Midget

Relax. It's a damn good joke even if it is an old one, and not the slightest bit offensive to me. I should have put a :-) or LOL in there I guess!

Besides, any man who drives a small convertible has to be fairly secure in themselves, people do tend to presume... (and that's *definitely* meant to be a joke!!)

Growler

Just checked again cant get it to move but holds air and the timing moves a tad when I reconnect the vacuum pipe. So I guess it works.
Growler I tend to agree small covertables in OZ I have had the comment "do they make them for men too " .
Never had that when I had the car in the uk but then everyone drives 4 cylinder cars over there not 6's and 8's.
Ed
Ed H

Nah... People do presume, esp if your pushing 50 and never been married...but i cant imagine ever being married, i like being alone to much

LoL.

Prop
Prop and the Blackhole Midget

Prop
that means when its cold in the shed you can rebuild an engine on the kitchen table without getting a divorce . One of my mates founout the hard way!
That said I built an engine in the dining room and didn't get into trouble. It was the missus engine though.
Ed
Ed H

Ed,
it's a good idea to keep those old dissys regularly lubed at services and check how much they've worn as





if you don't




they can cause



a lot of fiddling with your carbs :D



I've had a few cars that some others called 'girly' usually by older women strangely, if there's one thing girly it's that kangaroo p*ss they're forever advertising over here that my mate who's just come back from a visit to Aus swears he hardly saw over there
Nigel Atkins

Growler. Do not give a rat's tuti if you are gay. I admire you because of your technical competence. No more need to be said.

As to the basic question at hand, the vacuum advance can should be marked with something like 4-15-10 which would translate into the vacuum advance should begin at 4" of mercury (Hg) and be fully on at 15" of Hg and should provide 10 degrees of advance (not sure about where the ten degrees should take place--ten degrees of distributor advance equals twenty degrees at the crankshaft).

My own experience equates to most of the others. I do not seem to be able to "suck sufficiently" to activate the vacuum advance capsule, particularly, by mouth. Nor, is my mouth calibrated to allow me to accurately determine the inches of mercury that I may be sucking.

Thus, as suggested, I recommend your invest in a good quality vacuum gauge system and check out the vacuum system with it.

The system is designed to hold vacuum so that the additional advance will result in fuel economy. A leaking capsule will give an initial indication of full advance, but, then, bleed off. This means the capsule will not hold the vacuum and the overall ignition advance will be retarded from the "factory ideal"--which may, or may not, be ideal for the fuels available today.

Les
Les Bengtson

Very good Nigel, we digress but if you mean Fosters no one drinks it here
.you're more likely to see Guiness on tap than the 'amber nectar' !
Still back to the subject apart from having some clever vacuum pump and gauge I assume that there is no other test ? Even if it doesn't work the bob weights do most of the work IIRC.
Ed
Ed H

Ed,
I remember reading that dissys (from the 60s in the article) were out of wack within a couple of years of the cars leaving the factory

I'm all for the replacement fully electronic dissy, I've got a 123 it made such a difference throughout the whole range, if you want an even more original looking electronic dissy there's the CSI one too (I've no idea how good it is though)

as for Guinness that's all chemicals and advertising too, the Oirish black nectar
Nigel Atkins

Les
That explains it a bit more. So if it does not work worst case it will retard a bit. I guess the bobs will still advance enough to prevent it being too retarded. I presume it will just be a little inefficient.
Ed
Ed H

When i fitted my distributor found this video helpful
http://www.youtube.com/watch?v=cFfnenMFQ3U
mark (1977 1500 Midget) Preston Lancs

Here ya go, a mity-vac set for AU$35. Also comes in handy for bleeding that damned clutch cylinder, so it's an *investment*.

http://www.ebay.com.au/itm/MityVac-8000-Automotive-Tune-up-and-Brake-Bleeding-Kit-/400314048517?pt=Motors_Automotive_Tools&hash=item5d3493a005&_uhb=1

(The thing I've noticed with tools as investments is that those are the ones everyone wants to borrow.)
Growler

Ed. You are correct. If the mechanical advance is working correctly, you should see about 30 to 34 degrees of full advance at about 3,500 to 4,000 rpms. Some simply recommend setting the overall advance at 32 degrees at 4,000 rpms. I am not a fan of this myself. I have seen distributors where the mechanical advance was frozen in place and did not work. Thus, I like a stroboscopic timing light with a "dial back" feature. This allows me to to dial back the light, to the zero degree mark on the timing marks, and read on the instrument what the actual timing is. That allows me to see how my old/rebuilt/replacement distributor equates to the original factory specification for the year of vehicle I am working on.

As to the vacuum advance, you are perfectly correct. The purpose of the vacuum advance is to advance the ignition timing, when the engine is in a steady state, to provide increased fuel economy. The Lucas 25D4 had a mechanical advance only counter part known as a Lucas 23D4. The later Lucas 45D4 had a similar counter part known as the Lucas 43D4. The 23 series had no vacuum advance and provided, mostly with racing engines, a mechanical advance curve best suited for superior performance. But, at the cost of fuel efficiency.

Growler has noted the cost of the "Mity-Vac" system. I purchased one ten years ago, on the recommendation of someone on this forum, and have been very impressed with how well it works. Both for checking out what the actual vacuum advance was (this is interesting to check out and varies between dizzies) and for bleeding the brakes and the clutch system. An item worth considering if you can afford it. I am still using some of my Father's tools on, in his words, "your damned British Sports Cars". In fact, when I do so, I remember that these tools will go to one of my daughters, both of which have grown up around my Brit car preference and both of them will appreciate using my, and my Father's, tools when they work on their own cars.

My three year old grand-daughter has claimed my 79 MGB as her own and wants to sit in it and "drive it" when she visits.

Les
Les Bengtson

Les
Thanks for info, like yourself I always use a dial in timing light with my own marks (avoids lying on the floor to see the BMC ones)I prefer to know exactly what I'm setting the adv to, legacy of messing around with racing cars in the past. That said nothing else I've touched has ever had vacuum advance hence the questions.
Agree with you on tools some of my stuff is 80 years old and hand made. Thats what you need when you mess around with pre war stuff though.The Frog is what I would consider "Modern"
Growler, thanks for the link, have to give Santa a call. From what you guys have said it may help when I have to bleed the slave but I've yet to have a issue but I know lots of people do, maybe I've been lucky.
Ed
Ed H

The mityvac 8000...

I cant tell from the photo if its plastic or metal....i have the plastic one and I would NOT recommened it, it dosnt hold up well in the normal tossage of storage drawers and cabnits and the plastic dost hold up well with brake fluid residue on your hands ect....i would buy the metal version of the mityvac .

Id also consider buying a better quality vac gauge for the mityvac as the one that comes with the plastic one i have is barely a childs toy quality

But eventually ill buy a better quality mityvac... That said my plastic one is about 5 years old, so go figure

I guess you could always put a vac gauge on a penis pump and have it for dual purposes....hopefully thats not to gay, or im in trouble....hahaha

Prop
Prop and the Blackhole Midget

Prop. You don't have to be gay to be into auto- eroticism. Michael Hutchens wasn't gay and look what happened to him.
BTW. Your d*ck won't get any bigger with that pump you know. And No I haven't tried it!

Bernie.
b higginson

Ed

You should consider dismantling, cleaning up the insides and re assembling to ensure that the moving parts can all move freely. The bob weights in particular do gum up and become slow to move and return.

Your ability to fettle cars has always been impressive, your ability to cause lots of strange men to openly discuss their sexual preference is astonishing!

My new toy, 1932 vintage, is fitted with no such modern trickery. 6 cylinders and no vacuum advance.
Robin Cohen

Geez. Don't you people know how to suck? ;)

"You just put your lips together and breathe in" she said, --- kind of. He was most impressed.
Lawrence Slater

Ed,

The other way to see if the vac is leaking is to turn the advance plate by hand as far as it will go. Then plug the vac line with your finger, and let go of the advance plate. If it is not leaking, some of the advance will be held until you release your finger from the vac line, at which time the advance plate will return to the home position.

Charley
C R Huff

Gee charley

That sounds a little boring and "straight" forward

Prop
Prop and the Blackhole Midget

Charley

Now why didn't I think of that ...... probably because its far too obvious. Will give it a go when I can get back in the shed.

Ed
Ed H

No fans of Bogart/Bacall films here then.
Lawrence Slater

Lawerance with boggy and bacall....

You know boggy had a huge gigantic manhood, because before lauran bacall met boggy she had a sweet high pitched innocent voice after she meet him her voice changed to a low barratone very gutteral gravel sounding voice


Just saying... It could be just a coincedance

Prop
Prop and the Blackhole Midget

Nope I didn't know that Prop. I thought it was because of smoking, but now you mention it. lol.
Lawrence Slater

This thread was discussed between 14/12/2012 and 18/12/2012

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