65 rivi dual quad owners

[arnulfo de l.a.]

What are you using for vacuum to your distributor? Ported or manifold? I previously had mine ported but got some very bad pinging when accelrating on freeway. Changed to manifold vacuum and pinging stopped but now idles rougher. Is it a choice between the two? Thanks

[telriv]

PORTED   Rough because timing is too far advanced.

[DualQuadDave]

Ported is factory and correct.  You need to verify a couple a things if you are getting detonation.  Is your car a factory dual quad car?  Original distributor?  Check the base/total timing?  This is where you start.

[arnulfo de l.a.]

Dave, yes factory dual quad. I have not taken distributor out to verify that it is the right one for a gs but thinkinking it is because everything else is what it should be for a gs. Will check total timing next. What total timing are you at ?thanks

[gungeey]

Arnulfo are you saying it always has been pinging or recently started pinging

If recently did you switch gas/octane rating? recent tune up? Steve

[arnulfo de l.a.]

Always pinged when on ported vacuum. Switched to manifold and pinging stopped but idled rough. What teleriv states makes sense about too much advance on  manifold vacuum. Also i think they came with ported vacuum from factory. Im thinking todays gas is a big reason for the detonation even though i always use highest octane here in l a which is 92

[telriv]

Distributor limiting bushings worn out or gone. NOW would be a perfect time to rebuild, recurve & install electronic ignition.

, a service I offer.

Send me a PM.

 

 

Tom T.

[65VerdeGS]

My factory Gran Sport does not ping at all under any driving conditions if I use 94 octane unleaded fuel.  In my area this octane is only sold at Chevron stations.  All others brands max out at 91 or 92 octane.

 

The car pings lightly with 92 octane.  It's noticeable if you lay into it in high gear - detonation is light but noticeable and goes away once the load on the engine is lighter.

 

I use the factory initial timing setting, with everything else to factory spec.

 

Arnulfo - I would check your distributor spark advance.  Maybe your vacuum advance can is malfunctioning.  You can test a lot of this yourself using a Mightyvac test kit (about $60 in most auto parts stores).  Go to mightyvac.com for more info:

 

 

[arnulfo de l.a.]

Thanks for the help 65 verdegs. I have one of those pumps. Will check can as you suggest.also, thats exactly what mine does i.e. Pings when you lay into it in high gear. 

[1965rivgs]

Theres no doubt cutting back on the advance via checking total timing, etc will help with the detonation but it doesnt make much sense to me that ported or manifold vacuum as a source would make much of a difference in an "off idle" position? The vacuum levels should be approximately the same if the throttle plates are open. Are you adjusting/changing base timing when you change the vacuum source ? This would alter total timing...

Tom

[telriv]

Tom,

 

  Think about it. When you have ported vacuum the advance STARTS when you start to open the throttle blades. On manifold vacuum as soon as you touch the throttle you lose vacuum until you get to cruising speed & let up on the throttle. I still say one or both rubber limiters are missing.  I have them in stock. Have solved a few problems for others on the site.

 

Tom T.

[1965rivgs]

6 hours ago, telriv said:

Tom,

 

  Think about it. When you have ported vacuum the advance STARTS when you start to open the throttle blades. On manifold vacuum as soon as you touch the throttle you lose vacuum until you get to cruising speed & let up on the throttle. I still say one or both rubber limiters are missing.  I have them in stock. Have solved a few problems for others on the site.

 

Tom T.

 Yes Tom, I understand the vacuum dynamic at each location and the transition. But when the throttle blades are cracked and manifold vacuum is exposed to the ported nipple the vacuum levels should equalize instantaneously....correct?

 I agree total timing is not what it should be.

  Tom