Hi All. Thanks for your help on the last one. Here's a new one:
My 73 350 with rochester carb has the EGR valve capped off. The EGR valve is there, but the hose is just a cap and leads nowhere. I looked in the assembly manual and it shows the EGR going to a port on the front of the carburator. But, that port on the front of my carb leads to the distributor vacuum advance port instead. I'm confused. I've read some old posts about how capping off the EGR leads to better performance and better fuel economy, so do I just leave it capped off? THANKS!

 

I will preface my answer with a caveat-I am an old codger and very conservative. I believe the distributor should be connected to a port usually found near the right front corner of the carb low down. That is ported vacuum and is closed off when the car is at idle(the throttle is closed) the port on the front of the carb is full time vacuum. An engine with no crankcase ventilation will pressurize the crankcase forcing the gases contained therein to escape thru unintended avenues,very likely making a significant contribution to air pollution often forcing oil past the rings further contributing to air pollution and engine running poorly issues. Improper vacuum signals to the distributor will also contribute to air pollution and poor engine performance. Removing the vacuum to the EGR valve (I don't believe your car has one,is it maybe the PCV valve?) will often make the engine run better because engines are not very happy about breathing exhaust fumes(are you?) They don't seem to mind burning crankcase vapors.
It's your choice! If it were my car I would hook those items up as Chevy intended and check the timing according to a trusted manual.
I have been messing around with cars for close to 60 years and have pretty much decided that for street use cars set up the way the engineers designed them are almost always more user friendly that those modified according to what the neighbor said. On numerous occasions I have modified cars to the point that they were almost undrivable on the street. They were pretty fast,some were louder than others,some won a stop-light grand prix or two,most of them broke parts but over the long run a well-tuned stocker ran longer,cheaper and the wife would drive them. I have the best of both worlds,one is as stock as I can make it,the other is all kinds of modified and the wife won't drive either one!
Boy that was a lot of words to say little!

 

Hi Partsman! Thanks for the reply. I'd like to get it to be as correct as possible since I agree with you about it being set up the way it was intended. Here's what I've got:
The hose coming from the center/low of the carb goes to the pcv which splits off of the pcv valve to the vapor canister.
The hose on lower passenger side of carb goes back to distributor. (This is the one that the assembly manual shows as going to EGR)
The hose on lower driver's side carb goes to vapor canister.
Overall, the car runs great, but the EGR is not connected to anything. The EGR looks terrible (rusted look) and I am going to replace it. I just didn't know if I was going to continue to have it capped off.
Does any of this sound right? I can snap some pics too if needed for clarification.
Thanks!

Looking through the assembly manual:
I see that my PCV line is correct (low/center of carb to PCV which T's off to vapor canister).
I see that the lower driver side from carb is correct going directly to vapor canister.
It appears that the EGR should go to that lower passenger side port on carb (mine is connected to distributor).
So, if I switch the EGR to that port on the carb, where does the distributor line go? From the assembly manual and Doc Rebuild, this distributor line is supposed to go to the solenoid (where is that?). The distributor was switched over to Pertronix ignitor (no more points).

As you can probably tell, I'm going between garage, manual and computer to figure this all out. I appreciate your help!

 

Kinda wingin' it here,I have no direct experience with a 73 vette. I believe the "solenoid" referred to is controlled by a thermo switch probably located in the water neck for the upper radiator hose. Should show up on your vacuum line drawing. Those were very early days in the emission control business and ther were all kinds of weird things going on.
I read everything i could find in my Motorbooks 68-83 shop manual and they don;t call that EGR it's a thermo controlled valve to close off that side and cause the exhaust to go thru the intake to warm it up quicker. It is controlled by a thermo switch in the water somewhere. The only solenoid I could find was the idle solenoid and it could have been vacuum operated.
Wish I could be of more help!
Ron

 

Thanks again. I can see the drawing in the Doc Rebuild guide and in the assembly manual and it shows the solenoid right next to the distributor. The short hose goes from the distributor to this solenoid ("spark control solenoid") located right next to the coil. But, I don't have a solenoid there. I don't have the one near the upper radiator on the manifold either. So, I'm stumped. I guess whoever built the motor was a little stumped too since they just capped off the EGR. Thanks for your help.

Here's a link I found online:
http://www.wiringharness.com/tcs.htm
Sounds like it's no longer needed, but I don't know what to do with my EGR now.

I found more docs online. That TCS solenoid doesn't exist on my car. I found some diagrams of the hoses, but now need to find the electrical connections to the tranny (?). Here's the solenoid on Ecklers:
http://www.ecklers.com/corvette-tran...1973-1974.html
So, I think I know about the vac lines according to these diagrams. But, I now have to try to figure out the wiring to that soleniod. My tranny has no electrical connections. So, the question is now, do I just leave the EGR blocked off as it is?

 

Apparently there has been quite a bit of work done on the car. If you don't need to pass any inspections you can just leave it like it is. Seems to run OK,so best leave it as it is. To utilize the spark control solenoid you would have to go back to the stock distributor. Your trans should be a TH350 and they didn't have a lockup converter that's what the wiring to the trans is for. If you are really bored and need something to do,you could remove the EGR valve,cut the shaft and butterfly out of it and reinstall. To leave it out you would need a different manifold. Removing the guts would open that side a little,let it breathe a little better.
Good Luck!
Ron

 

Hey Ron. My tranny is now a Super T-Ten instead of stock. The car used to be an automatic and is now a 4-speed. So yes, there's been a lot of work done. I like your idea of hollowing out the EGR and leaving it plugged up as is. If it ain't broke...
Thanks again for all your advice. To take a break from the front end, I spent part of the day rebuilding the rear compartments. I like it when things go as they are supposed to with easy things like this.
Mike

 

I'm going to check out the vacuum pressure at the distributor and see if I can duplicate that off another port off the manifold. If so, I think I'll put the distributor on that other vacuum port and put the carb back on the EGR. Just a thought... And, that's only if the vacuum tests the same amount at both ports.

 

I made a plate out of 1/4" aluminum shaped like the base of the EGR valve and put a hi-temp gasket under it and held it down w/ the EGR valve clamp. Plugs ran a lot cleaner after that. The L-82 cam has a lot of overlap and tends to put a fair amount of the intake mixture at idle out the exhaust. Also run manifold vacuum to the dist., mech. advance all in around 2,200 rpm, and 12* initial.