I have run them on the machines both ways and have not seen any difference in relation to the spark position also. I am sure there will now be many replies to this.
Hook up vacuum advance, timing retards appreciably
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Gotta agree Don, with a mightyvac hand pump I'd be checking what happens when vac is applied to the can with cap off.
Another option is try another distributor, my guess is the problem goes away.
I have one here you can have cheap. PM me if you want to try it.
I have one here you can have cheap. PM me if you want to try it.
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THERE IS NO THING CALLED "REVERSE INERTIA". The centrifugual weights will advance the breaker point cam or reluctor tooth wheel AND rotor AHEAD OF THE DIRECTION OF ROTATION. The vacuum advance mechanism moves the only breaker plate OPPOSITE shaft rotation, advancing the spark.
BOB RENTON
Nacho-RT74
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Is just a thought
Using the small block driveshaft on a big block, or backwards, the centrifugal advance is also backwards, not just the advance plate move... it could be ( I think ) accidentally activated when rpms are slowing down hard. Just like when you are driving at high speed and press brakes. That's inertia, the resistence of an object on change its velocity or movement... I just called it wrong saying "reverse inertia", my bad...
Using the small block driveshaft on a big block, or backwards, the centrifugal advance is also backwards, not just the advance plate move... it could be ( I think ) accidentally activated when rpms are slowing down hard. Just like when you are driving at high speed and press brakes. That's inertia, the resistence of an object on change its velocity or movement... I just called it wrong saying "reverse inertia", my bad...
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Here you go. The plug wires are in disarray as I'd been moving them around to make sure I didn't have any cross firing going on.
I thought about the ported vs unported vacuum port. Decided vacuum is vacuum, and the only difference should be when it's applied. I did try both anyway, and got pretty similar results.
I'd mentioned in my first post the distributor came from a well known eBay seller....... but I don't wish to malign his good name, so hadn't mentioned it.
Anyway, thanks all for the great comments and plenty more to think about!
He's a reseller just like everyone else.... I doubt he puts hands on 99% of what he sells, but rotor phasing is real & his fix does work.. So it's worth checking.... If it is the problem maybe he'll cut you a deal on the fix...
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Your premise is all wrong again.
Perhaps this explains what the phenomenon is: Moment of inertia is defined as the ratio of the net angular momentum of a system to its angular velocity around a principal axis, that is. If the angular momentum of a system is constant, then as the moment of inertia gets smaller, the angular velocity must increase.
OR Inertia means just the state of the body, whether it is in motion or at rest. ... Moment of inertia is the measure of resistance of the object against rotation w.r.t an axis, which is also called as “Second moment of Mass/Area” it varies from axis to axis of the same body.
IF you need a formula to compute it, I can supply the formula....
BOB RENTON
Is that vacuum advance adjustable, where an allen wrench goes in vacuum port and needs adjusting. I know 0 about them, just wondering.
Very interesting! I don't doubt what you guys are saying. But, when I switched my wires "for fun" it popped and idled like crap..instantly noticeable.
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When you hook up the vacuum line to manifold it will pull added timing right away even at idle.
Hooking it up to ported won't pull a vacuum at idle and you won't see any timing advancement until you open the throttle a bit.
I'd try 12* to 15* timing without the vacuum hooked up then hook the vacuum line to ported and see how it acts.
Make sure all your plug wires have good contact at each plug also. Loose connection at the plug will cause a popping also.
What's the history on this engine? Has it ran fine before? Has it sat for a long time? Maybe something else is going on and not the dizzy?
If it was rebuilt (in china, for example) they could have gotten the wrong body (A) on the B/RB shaft. They spin opposite so the vacuum advance pulls in a different direction. Just spitballing as it doesn't seem probable.
If you check out the pics he posted of his distrib the can is on the correct side for a bb. The sb would be on the opposite side.
Thanks for the input. I understood the ported bleed wouldn't work until the throttle opened up. My point was hooking to either port got the same results, just at a different RPM, although I must say it didn't take much RPM change to cause the retarding action with the ported bleed. I'd double checked plug wires, routing, firing order and making sure they're securely fixed on the plug.
The engine consisted of a short block I've had for years, with forged flat top pistons. It had been a good running engine. The heads were a fresh set I've had on the shelf. I had thought about possibly an exhaust valve sticking or not seating properly, so I listened to the exhaust note for some time and it seemed to sound good out of both sides. Rocker arm assemblies were out of a very low mileage engine and look like new. The cam I know was a good used purple shaft which I'd put in it a long time ago but never got back to it. Lifters and lobes on the cam looked like new as well. I replaced the distributor drive gear bushing just for peace of mind, when I assembled the engine. Timing chain was used, double roller, but didn't have 1000 miles on it because I'd pulled it when I converted to a 3 bolt cam setup in a different car. Cam installed straight up: no advance or retard bushings.
With the vacuum advance disconnected the engine sounds very good. Not any sign of a problem. I let it sit and idle for a good 20 minutes. Revs up fine, settles right down and idles well. Tried the advance again on ported bleed, same results. More or less initial timing and same results. As you might expect, with less initial, the exhaust banging gets more pronounced since the timing goes even further ATDC.
Certainly a good mental exercise for me!
I would have switched out that screwed up distributor for a known good one long ago.
Did happen to check if vacuum advance is adjustable? Think a small allen wrench is used to adjustt.
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If the can has a hex shape to it, it should be adjustable with a allen wrench. Thing is he states that it retards the timing when he hooks up the vacuum advance.
You could pull a vacuum on the can with the cap off and see which way the advance plate turns. You can use a longer hose and suck on it yourself to see, if you don't have a hand pump.
OK I am kind of thinking the ported vac is not working right and it is giving full vac at idle and when you rev it the engine vacuum decreases so it will retard. That's could why it is the same on both of the ports. Have you hooked up a vacuum gauge yet?
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