Ordered a set of 3 "rebuilt" Rochester carbs for my 283. I bought the car with three 2 barrel rochesters on it but only the center one was hooked up. The other ones looked pretty bad so I got the "rebuilts". Bad idea. They run terrible, won't even run on the center one. I learned new paint, new screws, and a carb kit does not make a new carb. Seller was very nice and agreed to a full refund even the shipping both ways. So....I just ordered Speedways 3 carb kit with manifold. It has the super 7 carbs, (stromberg clones). My question is : The stock, ( I****ume ) 283 distributer on my engine has a vacuum connection that went to a port above the*****erflys on the center rochester and a mechanical centrifical advance. The "stromberg" carbs have no vacuum port above the*****erflys and the tech said to reley on the mechanical advance only. Is this ok? Why does this distributer have both mechanical advance and a vacuum connection too? Thanks
I would connect the vacuum advance. It will run better. You could do like the old 348 engines and tap the vacuum through a hollow carb stud. The 348s had a hollow stud on the rear carb mount and accessed the vacuum advance there.
Your mech. advance will kick in above idle, just when your vac advance starts to fall off. You want to use manifold vac instead of ported. There have been discussions to the end of the earth on which way is right or wrong. Idling in traffic temps will be cooler with vac adv. hooked up to manifold source.
Is there a vacuum port in the manifold between the carbs? Get your mechanical advance to come in totally before 3000 rpm. Light springs, heavier weights.
A little off the topic, but 3 stock rochesters can't simply be used in a tri-power configuration. You need to set them up properly for the application... The outermost*****erfly's need to close fully at idle, idle circuit on the center primary only, use progressive linkage, plus other tricks to get them to run properly. I'm using vacuum from my carb base casting (below the*****erfly's) for my advance mechanism. Once dialed in, they are badass. I have this setup on my 283 on the truck in my avatar. It screams....and rattles, and shakes! But it's kewwwwwl. Good move ordering the full kit. Let us know it runs.
You definetly want to run a vacuum advance to get the best part throttle (cruise) drivability. Do not hook it up to a manifold signal, it will pull the base timing ahead of where it needs to be and you'll just end up having to back it off by retarding the distributor which results in gaining absolutely nothing. Ported vacuum signal is (should be) available when the throttle blades are just cracked open a little bit, at light load cruising. The vacuum advance is there to light the fire eariler at cruise rpms where the air fuel mixture is leaner than at idle or WOT. Leaner A/F mixtures burn at a slower rate which is why they need to be ignited with a bit more timing advance, to get the most bang for the buck I guess you can say. Every single SBC that I've tuned came in barely running, running extremely hotter than normal, and was all around unpleasant to drive. Almost every single one had someone who knew how to "tune" an engine hook the vacuum advance to a manifold port instead of the ported vacuum on the carb, or it was blocked off all together. Once it was hooked up correctly, with correct base and total timing dialed in and proper A/F ratio set, the owners were all blown away by how much better their cars ran. My friend said his Impala felt like a race car compared to when he bought it and it ran like dog*****. Guess where the vacuum advance was connected. You are right that strombergs do not have this port, so the other option would be to switch to a full centrifugal advance like stated above and have your timing curve dialed in to compensate for part throttle driving without the vacuum aid. I have a Mallory full centrifugal advance set up and I am pleased with how well it performs on my flathead with 2 strombergs. Just have to play around with it a little to give the engine what it likes.
If you time it for manifold vacuum it will also be fine. Vacuum "advance" is a misnomer depending on the state/style of tune. It can also be a LOAD COMPENSATION DEVICE which retards timing under load at the crack of the throttle. Manifold vac can also aid in hot starting on some engines. It's also correct that some engines like ported vacuum, but there's never a "this" or "that", and ESPECIALLY on hopped up SBCs. Just sayin, carry on...
I can't thank all you people enough. I had to stop reading a few times and let my senior brain cool down,and catch up because it started saying "overload, overload." But I think I've got it, or most of it, or enough of it. I'll hook the distributer into manifold vacuum, as well as the crankcase vent valve into manifold vacuum. It's a stock 283 and stock distributer as far as I know Carbs and manifold kit from speedway should be here in a few days. Thanks again Wayne
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