1970 vette vibration issue
 

ok old thread is getting long so let's try this. i have exhausted all the other things that were talked about on the 1500 to 2800 rpm range for this vibration issue. i found a broken mount drivers side i found a bad distributor and fixed that. he had to put the points back in due to burning up the pertronix. we changed the h balancer and all of this made no changes. then while up on the hoist i looked for anything that may be touching or close enough to touch.

now he was at a car show and saw a car that has the tcs all connected to the distributor. so we looked into this and found out this is a transmission controlled shifting system and the trans controls the timing. well some in that thread said they just removed it and reconnected the vacuum advance to the carb.

so now if the tcs system is not necessary can someone tell me where the vacuum would go from the distributor vacuum advance unit to the carb. i have included a tcs vacuum routing picture and maybe someone can tell me the port number on this picture so i can connect the dist up to that port and see if the vibration goes away and he has the performance back. i'm thinking port 4. he used another port on the side of the carb not even port 3 this picture shows, thanks for any help in this and maybe this will help take away that vibration being i have found no mechanical issues with it. bp.

https://repairs.willcoxcorvette.com/...oid-1970-2.png

I always connect mine to one of the carburetor ports that has manifold vacuum all the time. I think originally mine was connected to a ported vacuum which meant that there was no vacuum to the distributor until you got off idle.

that is kind of like just setting the advance to the max like ron is now doing. then you have full advance on all the time. there is a reason they use the ports for these.

Not at all. As soon as you start opening the throttle under load, the manifold vacuum starts to decrease.

that is the opposite of the normal way the get connected. when the throttle is closed no advance the vacuum module hols it to the idle but when you start to open the throttle then it gradually pulls the vacuum open.

your way start out with full vacuum and decreases with open throttle. it that was the way to connect then the mfg would be doing that.

Are you saying that manifold vacuum increases with throttle opening under load?

that port the connects to the advance decreases under load so the fuel charge will not bang on the crank and give you spark knock. but as the throttle is opened normally you do get an increase in vacuum i went thru this on the corvair forum about the vacuum port those cars use.

What I'm trying to say is that the port you connect to should be below the throttle plates so that it will get the direct manifold vacuum which decreases with the throttle plates opening.

yes that is the port that has no vacuum when closed and as you open the butterflies the vacuum does increase. if you put a vacuum gage on it you will see the vacuum change as the throttle opens the vacuum should increase. so if you have it connected that way your doing the same as the mfg do.

That's what I call a ported vacuum port. That's probably what the vacuum advance was hooked to when it came from the factory. The whole purpose of vacuum advance was for economy, not performance.