11 replies to this topic

[ac427]

How to test for mechanical advance in a vacuum advance less setup;

 

Am i right in thinking i just need to:

1. Set the timing light to 32 degrees of advance,
2. Raise the engine RPM to 4000
3. Check to see if the timing mark on the crank pulley is near zero ?

 

 

[Cooperman]

If you suspect that the mechanical advance is not working fully and correctly, I find it easiest to mark the installed position, take the distributor out, dismantle it and clean and lightly oil the bob-weights. It's about a 1/2 hour job and once done you know the weights are free to move correctly.

I had a problem with an Innocenti 1300 I had a few years ago. After a full restoration it would tickover fine, but when I drove it, it was hesitant aometimes. I checked everything electrical and fuel-related. I took the carbs to pieces and polished the dashpots, changed the coil and condenser, etc. Finally I took out the dizzy, stripped it doen and found the bob-weights  were 'sticky'. A wash in brake & clutch cleaner and some 3-in-1 oil and it was cured.  

[KTS]

 

How to test for mechanical advance in a vacuum advance less setup;

 

Am i right in thinking i just need to:

1. Set the timing light to 32 degrees of advance,
2. Raise the engine RPM to 4000
3. Check to see if the timing mark on the crank pulley is near zero ?

 

 

..only if the distributor is seized at 32degrees advance (..technically 16degrees distributor advance)

 

if the advance is seized, then the timing light should show the same advance (..whatever it's stuck/set at..) at all engine speeds

Edited by KTS, 06 September 2023 - 01:53 PM.

[ac427]

If you suspect that the mechanical advance is not working fully and correctly, I find it easiest to mark the installed position, take the distributor out, dismantle it and clean and lightly oil the bob-weights. It's about a 1/2 hour job and once done you know the weights are free to move correctly.

I had a problem with an Innocenti 1300 I had a few years ago. After a full restoration it would tickover fine, but when I drove it, it was hesitant aometimes. I checked everything electrical and fuel-related. I took the carbs to pieces and polished the dashpots, changed the coil and condenser, etc. Finally I took out the dizzy, stripped it doen and found the bob-weights  were 'sticky'. A wash in brake & clutch cleaner and some 3-in-1 oil and it was cured.  

 

 

 

How to test for mechanical advance in a vacuum advance less setup;

 

Am i right in thinking i just need to:

1. Set the timing light to 32 degrees of advance,
2. Raise the engine RPM to 4000
3. Check to see if the timing mark on the crank pulley is near zero ?

 

 

..only if the distributor is seized at 32degrees advance (..technically 16degrees distributor advance)

 

if the advance is seized, then the timing light should show the same advance (..whatever it's stuck/set at..) at all engine speeds

 

Thank you all. The symptoms are that the engine well rev up fine at idle but when i go to drive away it will do no more than five MPH. So i have been attributing this to the advance required under load no being present.

 

The carb dashpot, and piston are all in good nick. The leads, spark plugs and distributor cap were replaced just because they were 20 years old and that was when the engine was last run. This is why i suspect the distributor is sticking.

 

I should take the distributor out and just overhauls it as part of the maintenance but i thought a timing light my prove the theory that the distributor is at fault?

[KTS]

if you have a timing light, then you can use it to check/confirm what's going on, but after being stood for 20years a strip down and overhaul would be a good idea anyway

[nicklouse]

Cap off. Grab the rotor arm twist. Look inside and you should see the bobs move. 

[Lplus]

Set the timing light to zero advance, Highlight the timing marks with paint or whatever, run the engine and rev it up.  If the mark on the pulley moves anticlockwise the mechanical advance is working.  Also this should give you a chance to check the timing at low RPM is sensible - likely anywhere between 5 and 10 degrees btdc

[nicklouse]

In addition to my post above you have to consider the vacuum advance as that works in a different range to the mech advance.

[sonscar]

In my experience if the timing is close enough to start and idle it will still have reasonable flattish performance.As said start it and see what it does with higher revs.As nick said try the vacuum advance,suck in it,is it correctly connected?Steve..

[Spider]

Distributors wear in all manner of ways. A commonish wear issue, aside from the Bushes in the Body, is notching of the Bob Weights. These will cause erratic operation of the Advance Mech and not always show up well when trying to test on car. Worn springs is another - they wear on the looped ends, these too can cause sticky and erratic operation. Seriously, having tried various on-car methods of testing, I gave up long ago and bought a Distributor Tester which I've found indispensable. I know not everyone has an on going use for one or would want to buy one, however, I'd suggest having the distributor in question tested by a reputable firm who has such a Tester.

 

 

[68+86auto]

Inspect it by removing the cap and turning the shaft first.

 

Check the dwell (assume points fitted)

 

check the timing at say 1000rpm first by adjusting the degrees on the timing light until it lines up to 0°. That is the timing at that rpm. Now repeat that at various rpms, set engine to rpm and then adjust the timing light until it lines up with 0°

 

write down the degrees on the timing light and rpm at each test.

 

Ideally this should be done from a high rpm and then decrease the rpm and test again.

 

If the test of turning the shaft by hand passes and the idle timing is correct then I don't think the advance will be your biggest issue.

[coopertaz]

if points are fitted is the dwell correct, the symptoms you suggest used to occur if the points slipped reducing gap.