Alrighty, I've looked, searched the HAMB, ran the google (found the free rochester 2g manual though!) and havent found what I'm looking for. I'm installing my offy intake with 3 2g carbs, I need to run, my vacuum assist for me brakes, my vacuum advance for my carb, and my vac port for my trans. being as this is my first venture into a 3x2 set up I want it right. Unlike the weiand intake I just pulled off I only have one small vac tap into the manafold (looks to be 1/4") I was thinkin plumbing the trans into that (constant vacuum right? T350 trans btw) and the brake boost into the carb base. my question (if the above are right) where does the vacuum advance for the distributor go? Does that go into the base of one of the carbs as well? or am I totally wrog here and need realigned? (thats fine too) For those that are schooled in the fine art of multi's I could use your knoledge and yes if I'm totally off the mark here I welcome the hand that setteth me straight
Both the trans and the brake booster should be tapped into the manifold for full vacuum all the time. The dist vacuum would go on the center/primary carb base.
I have the distributor vacuum advance and the transmission vacuum all coming from the manifold. I don't have a brake booster, so I can't help you with that one. I learned from another site that having distributor advance connected to the manifold vaccum allows the motor to run cooler. I believe it's because if you used the ported vacuum from the carb, the timing is slightly retarded at idle and causes the engine to run leaner and it runs hotter. I know there has been a lot of debate on whether you should run ported vacuum or manifold vacuum to the distributor advance, and this is how it was explained to me. Others may have a better explaination on all of this. I have a 't' fitting on the fitting coming out of the manifold and hooked both lines to it. It works for me and my motor doesn't heat up like it used to in slow traffic, when cruising. Red
alright, I can deal with that, that said would it be acceptable to T off the port and run the trans and the brake booster off the same port?
Yes, that is how it is done from the factory. The brake booster and trans are not open to the atmosphere at any time so they won't mess each other up. Both just use the vacuum to move a diaphram. I've seen some diagrams in shop manuals that have four different things on the one port.
I don't know about Multi Guru, but I'll step up... -Vacuum for power brakes; take it from throttle body of centre carburator. Put there hose and Y-connector, so you can divide it to two, and take vacuum for trans also. (Less hoses over engine) -Another way would be taking vacuum from intake manifold. (There's constant vacuum) -Distributor vacuum is taken from carburetor body. Check this pic of my Buick's engine; Copper piping from centre carb goes to distributor. Chromed piping from rear of centre carb goes to power brakes. (That is the one you can divide in two for trans and PB. Btw, do I remember right, that TH-700 and Dynaflow are only GM-transmissions that don't need vacuum?? I may be wrong also?) Hopefully this helps? Are you building your set-up yourself?
Did someone mention a FREE Rochester manual? Where is it at? What are you using for jetting on your 6-pack? PanheadGuy
Carb-otto, No I didnt build it myself, I wish I could claim it but alas, I cannot. I was a good deal whore and picked it up already done. thanks for the pics and the guidance, its helped a bunch, I should be ready to fire it up here in the next little bit. to those looking for the manual, yep it be free, but its online...not entirly sure if you can save it as a PDF or not....I just chucked it into my favorites. here is two links, one is to the main site the other is to the manual direct (the main site link gives you a tabbed index) http://www.tocmp.com/manuals/Carbs/Rochester/2-Jet/1964Manual/pages/64Rochester2Gmanual_0001_jpg.htm http://www.tocmp.com/manuals/Carbs/Rochester/2-Jet/Manual/index.html
Salty, Just be sure your distributor is hooked up to the port with NO VACUUM at idle and lots past 2000rpm. In other words, it is venturi vacuum and not manifold vacuum you want your vacuum advance canister to see. Hope this helps...KT
I don't know what dizzy you guys are using but the 60's SBC dizzys that I'm familliar with ("window points") had vacuum at the dizzy at idle. If I missed something forgive me. The first step in setting the timing on a mid year 58-60 Chevy or Olds is to disconnect and temporarily plug the vac advance line. (they moved the vac conn. to the intake mid year 58 according to the newest book that I have) WHY? because the vacuum at idle will give you a false reading. For Buicks of those years they say to set the idle speed to 400 RPM, before using the strobe light that's 400 RPM, anything more and the vac will give you an inaccurate reading. With the vac unplugged on a Chevy you set the initial timing with a light. I would keep the light hooked up after I reconnected the vac line to the advance can and the timing would jump off the tab on the timing cover at idle (SBC) and the idle RPM would jump up a tad. That confirmed that the advance was still working correctly. Life was good. There was supposed to be vac at the dizzy at idle. If there was no vac at the dizzy at idle it would be a waste of time to disconnect it. Look up "setting the timing" in a Motors Manual from that period. They used the same basic dizzy until the HEI dizzy. That's how I set the timing on my 63 340 HP 327 and my 69 427-390 so I don't think they changed the design. If you are using some aftermarket distributor system then I may be all wet but if it's a SBC window points dizzy I think you need manifold vac to the advance can... at least that's how GM did it. It's probably not that critical but if you want the advantages of a vac advance dizzy I'd hook it up like the factory did. IMHO PS I don't know shit about HEI dizzys and I'm not interested in learning.
Did you say a TH350 trans ?? I didn't think they used a vac modulator..uses TP cable ?! If you should need a raw(manifold) vacuum source you could use a hollow carb. mouting stud. GM did this. Use your intake port for brakes and any vacuum sorce above the throttle butterflys for ported vacuum. Carb-Otto happens to have one of the 2g carbs with a ported vac port. Some don't have it. Plus I see idle air screws on end carbs...not necessary on tri-powers..I assume he just has them shut down. BTW: Nice clean set up Carb Otto........I've messed with Pontiac Tri-Powers for years now. Early Pontiac's did use manifold vacuum for distributor because it got rid of loppy idle with performance cams...and to me made it more responsive with long duration cams. However your distributor should be properly set up also...
I ran a 3x2 on my SBC with Rochesters. This set up is from vintage speed, i did not have power brakes but if i did i would have run it from the manifold or from the 1/4 inch pipe tapped hole in the center carb base plate. The distributor and tranny vacuum could also be taped off of this location or use the rear carburator base plate 1/8 inch pipe taped hole. The other location for the vacuum for all three applications can also be taken from the manifold it self. On a Offenhauser 3x2 intake there is a 1/8 inch pipe taped hole that can be used for the trans and distributor by using a 1/8 tee fitting to conect the dist and trans to the maniflod. Some people say to use ported vacuum for the distributor but thats not the correct place to put it. Ported vacuum comes from area above the carburator throttle plates and draws more vacuum as the engine rpm increases due to venturi effect.This was common during the smog engine 1979's area. If you have a vacuum advance dist and its working properly you will have the timming advanced beyond the initial timing setting at idle wich gives the engine a better idle quality but will retard the timming when you put your foot into it. Call me if you like 810-569-5515
The 350 uses a cable for telling the trans when you are at full throttle. It uses a vac modulator to tell the trans that you are "cruising" (high vac) and to shift to high gear. Ported vacuum on a SBC points dist will give you poor mileage and not total enough advance.
Thank you 60man. Yes, there are air screws on the end carbs, reason is that this set-up is built from old carburetors which were used on 2-bbl intakes; not original tri-power intakes. Original tri-power carburetors differ little bit from those; carbs which were originally meant for 3x2, have thicker butterflies, smaller levers on side carbs etc. 60man, Do I remember right that Pontiac has set-up that has big-base Rochesters on the side and small-base on the center? Olds 4-4-2 had that same for year '66, and if I remember right, Pontiac had this set-up '59-'66 ?? Correct me if I'm wrong? Are you running vacuum controlled linkage for progressive operation?
The Jalopy Journal
