Does this dizzy look good?

[dom14]

Hey guys,

This dizzy was running on my RB30 Patrol for a while.
It is the spare one, but I had it on for a while.
Basically I put it to test it months ago and then forgot

I pulled it out to have a look 'cos the vacuum advance appeared not responding.
(pulling the vacuum line out of the vacuum advance diaphragm seemed to have no effect on idling rpm,
so I suspected a blown vacuum diaphragm).

Upon opening it up, below is what I've discovered. The rotor & dizzy cap is covered with whitish kinda crud.

What caused it? Blown vacuum diaphragm?
Is it 'cos excessive carbon buildup inside the cylinders?
Or is it 'cos of bad ignition & timing(which also can be from carbon buildup?)??!!
Any thoughts, advice?

Thanx

[taslucas]

I didn't think vacuum advance had much effect at idle? Isn't it for higher up in the revs?

>>>tappin from tassie

[dom14]

I didn't think vacuum advance had much effect at idle? Isn't it for higher up in the revs?

>>>tappin from tassie

Yes, I think that's right.
But, if you remove the vacuum advance hose when idling, the rpm suppose to jump a bit high?!!

[GeeYou8]

The vacuum advance line is before the throttle butterfly, when you open the throttle and suck more air through is causes a small change in pressure that operates a diaphragm to advance the ignition timing, there are mechanical weights that advance the timing with engine RPM too.
At idle it wont do much at all, if you hook up your timing light and rev the engine with and without the line attached you should see a bit more advance with it attached. Better still if you have a hand vac pump you can connect it to the dizzy and watch the timing move when you pump it, that will also show if it is leaking.
As for the spare dizzy, it looks like corrosion, give it a clean. Grab the rotor an wiggle it, there should be no lateral play, attach a clean hose to advance line & suck on it, it should hold suction when you suck.
Graham

[dom14]

The vacuum advance line is before the throttle butterfly, when you open the throttle and suck more air through is causes a small change in pressure that operates a diaphragm to advance the ignition timing, there are mechanical weights that advance the timing with engine RPM too.
At idle it wont do much at all, if you hook up your timing light and rev the engine with and without the line attached you should see a bit more advance with it attached. Better still if you have a hand vac pump you can connect it to the dizzy and watch the timing move when you pump it, that will also show if it is leaking.
As for the spare dizzy, it looks like corrosion, give it a clean. Grab the rotor an wiggle it, there should be no lateral play, attach a clean hose to advance line & suck on it, it should hold suction when you suck.
Graham

Thanx mate.
Yeah, the idling rpm drops when the dizzy vacuum advance disconnected and diaphragm is vented to the atmosphere.
It does show that clearly on idling, and makes sense as you explained above.