Vacuum advance

moggyadventurer · Post by **moggyadventurer** » Thu Dec 10, 2009 8:23 pm

Hi, I have recently read on a previous forum about people changing the vacuum system on the distributor. For the novice I am, can someone explain the symtoms of the vacuum not working correctly. Thanks

Post by **PSL184** » Thu Dec 10, 2009 10:11 pm

Easiest way of telling is that the acceleration will loose its "sparkle". Best way to check is to suck on the vac pipe with the dizzy cap off and see if teh baseplate moves....

Post by **bmcecosse** » Thu Dec 10, 2009 10:57 pm

Welcome to the forum! If the vacuum is not working - then to get decent idling folks advance the ignition timing - and then it's hard to start the car because it kicks back against the starter - and the overall advance comes in too quickly and 'pinking' occurs. As PSL says - suck the tube and watch the baseplate. The 'sucking' should generate a good vacuum - if it flows air then the diaphragm is broken - if it holds vacuum and the baseplate doesn't move, check to see if it is seized or if the return spring is broken or dislodged.

moggyadventurer · Post by **moggyadventurer** » Fri Dec 11, 2009 7:46 am

Hi, Thanks for this will try today.

Keep on motoring!!

linearaudio · Post by **linearaudio** » Fri Dec 11, 2009 9:09 am

moggyadventurer wrote:Hi, Thanks for this will try today.

Keep on motoring!!

What none of the "old hands" has warned about is the distinct possibility of sucking in a mouthful of stale petrol when you do this test, as it tends to get drawn into the diaphragm over time, very unpleasant.
Having been caught out a couple of times, I now remove the dizzy cap and the vacuum pipe at the dizzy end, then move the points mounting plate clockwise against the spring. This won't neccessarily prove anything, BUT, if the vacuum advance is working and there is fuel trapped, it will be ejected by this action, rather than you ingesting it! If none shoots out, it is then safe to re-fit the black tube and do the sucking bit!

Post by **Declan_Burns** » Fri Dec 11, 2009 9:21 am

I used a plastic syringe for checking the vacuum advance. A handy tool and it is also very useful for topping up the oil in the dampers

Post by **bmcecosse** » Fri Dec 11, 2009 9:29 am

Softies!

Post by **mike.perry** » Fri Dec 11, 2009 12:05 pm

You get the best results when the petrol vapour gets drawn past the split diaphram into the distributor and then explodes when the points spark. It makes a mess of the dizzy.

Post by **bmcecosse** » Fri Dec 11, 2009 5:51 pm

No smoking then!

moggyadventurer · Post by **moggyadventurer** » Sat Dec 12, 2009 9:18 am

Hi to you all,
Having now tested my vacuum, it does appear faulty. However on further examination of the dizzy, there seems to be a lot of play on the cam itself - it has done 110k! I was reading in a previous forum about people who have struggled with timing (pinking) underload due to worn out dizzy, this sounds very similar to my moggy.

Does anyone have any recommendations on a new dizzy (esm, bull motif, simonbbc) - I would like to keep it "points" based.

Post by **bmcecosse** » Sat Dec 12, 2009 9:27 am

If there is considerable sideways motion in the dizzy -then yes -may be an idea to change it. Make your own choice if going for a 'new' one - but perhaps a good used one would do ? Not heard of 'simonbbc' before - but their 45D4 looks good value at £32.99 - just make sure it will fit your A series (ie NOT A +) engine.

moggyadventurer · Post by **moggyadventurer** » Sat Dec 12, 2009 9:47 am

Hi bmce,
They do a 25d4 for about 45pound (pound sign key not working on keyboard), and I have a feeling they supply bull motif (10miles away). What about curve settings though? I've heard this mentioned before about dizzys

linearaudio · Post by **linearaudio** » Sat Dec 12, 2009 9:47 am

bmcecosse wrote:If there is considerable sideways motion in the dizzy -then yes -may be an idea to change it. Make your own choice if going for a 'new' one - but perhaps a good used one would do ? Not heard of 'simonbbc' before - but their 45D4 looks good value at £32.99 - just make sure it will fit your A series (ie NOT A +) engine.

Interesting electronic conversion for £20! Can't see what it uses as a trigger, the cam itself?

Post by **bmcecosse** » Sat Dec 12, 2009 10:57 am

Doesn't matter - petrol has changed significantly since the original dizzy curves were 'designed' - I would go for the 45D4 - it's a better/later design of dizzy!

Post by **Alec** » Sat Dec 12, 2009 5:54 pm

Hello BMCE,

"it's a better/later design of dizzy!"

If it is that would be a first, usually the newer the design the cheaper built. Didn't the early Cooper 'S' have a better engineered distributor based on the 25?

(talking of poor design distributors, how do you get on with the TR7's Delco Remy. I fitted a Dolomite Sprint Lucas one to my son's 7.)

Alec

Post by **bmcecosse** » Sat Dec 12, 2009 7:44 pm

The S version of the 25 was just the same - but no vac advance - and stronger spring on the points. Later 45D dizzy has the assymetric shape on the rotating contact block - also larger diameter cap etc to reduce chance of arcing between contacts.
My dizzy has lumenition fitted - I leave it strictly alone! I do have a complete spare (on points) that I carry with me. But i agree - it's a nightmare of a thing - which is why i leave well alone. You haven't said your son has a 7 before - has he had it a while - or since I picked up mine - from Oswestry? And - is he on the TR7 forum http://www.forum.triumphtr7.com/ ??

Post by **rayofleamington** » Sat Dec 12, 2009 8:46 pm

Strange advice so far regarging 'noticing a change in accelleration'.

The vaccuum advance is in fact a FUEL ECONOMY device.
It makes no effect on accelleration - when you've foored the accelleraor pedal there will be NO vac advance..

The function of the vac advance is merely to advance the spark when the engine is at light throttle. At light throttle the cylinders have a lot less air in them, so the spark can be made earlier without pinking. An earlier spark gives a little bit more power - hence the improvement on fuel economy.

Therefore a failed vac advance diaphragm will just cause reduced part-throttle mpg.
If the rest of the dizzy is faulty (failed load springs or dodgy rotor-weight performance) you would be more likely to get pinking.

The rotor-weight mechanism is to advance the spark at higher revs. The advance (in degrees) does not cause an advance in the timing - because at higher revs it takes less time to do more revs.

Post by **bmcecosse** » Sat Dec 12, 2009 9:20 pm

Don't see any mention (in this thread) of acceleration? But - the vacuum advance does make the engine 'brighter' - if it's failed, the engine is very 'flat' to drive - sluggish to pick up. With working vac - cruising along on part throttle gives high vacuum, the advance pulled well up - when you floor the throttle - it holds up for a short period and allows the engine to respond quickly. On my car there is usually a transitory 'chirp' of slight pinking at this point! But indeed - it's main function is as an economy device - and very essential these days too!

Post by **mike.perry** » Sun Dec 13, 2009 1:34 am

My Minor certainly felt down on power with the vacuum advance not working.

Post by **Alec** » Sun Dec 13, 2009 8:24 pm

Hello BMCE,

it's a few years ago since he had it and since been sold. Not so much af an enthusiast as I so no, not on any forums.

Alec