I have a 67 300 with the 4 barrel intake with a edlebrock 1406 (600 cfm) carb. Other than a isky 262 cam, pertronix and headers its pretty much a stock engine. Just wondering if the carb is a bit too big for it, based on a formula on the internet I should have a 500 cfm carb. Right now having some issues with timing and carb idle, gets some run on issues as well, maybe I just haven't found the right sweet spot but could this carb be some of my problem. Should my timing degree be more than the stock 2.5 with the cam I have now? Thanks for any advice
The answer to this question will depend on whether you have the original distributor. Your car is now more than 50 years old, so unless you have owned it from new, and know it's entire history, you can't answer that question until you check the distributor part number. The 1967 engine came with distributor part number 1111158. Your question is why I authored the Power Timing Thread years ago. Most only concentrate on initial timing disregarding what happens as soon as you go above idle speed and drive the car. Mechanical and vacuum advance add ignition timing which reaches a maximum at some RPM. Distributors that came on Buick engines over the years differ in the amount of mechanical advance that is built into them. The total advance you want to run, and the distributor that is installed in the engine determine what the initial timing HAS TO BE. I can tell you that most aftermarket cams will want more initial timing to idle well. The bigger the cam, the more this is so. You can't just bump the initial timing without also increasing the total timing unless you modify the distributor for less mechanical advance. Also, no off the shelf carburetor is perfect out of box for your modified engine, it will require tuning. BTW, Buick guys have a good laugh over the CFM calculators for carburetors. 600 CFM carburetor is most likely not too big. It would probably been better if the carburetor was like a Carter AVS where you could adjust the secondary activation via an air valve like a Q-jet. I hope you are running vacuum advance off of manifold vacuum so that it advances your timing at closed throttle idle. That is the way it was in 1967.
You might want to put a vacuum gauge on it also. I would say you should get 15 inches vacuum at idle with that cam. As mentioned manifold vacuum controls timing vacuum. Not carb which is ported vacuum. That carb tends to run rich down low and leans out as rpm climbs. So jetting to your engine is required. An air fuel meter may be helpful for that.
Yes I am using manifold vacuum and I've always thought it runs a bit rich at idle speed so that answers that question. Distributor is original to the engine and it has only had the pertronix upgrade. When I advance it a couple of degrees it seems to cause the run on when I turn the ignition off and when it's turned back it doesn't run in gear for very long. I do have a vacuum gauge meter and it says late timing ignition. I must be over thinking the simple fix.
the edelbrock 1406 is an electric choke model and so is set up a little more towards economy . the manual choke models lean towards a performance set up . just jetting and metering rod etc changes . no huge dif . you can look around for a used 500 cfm version and rebuild one but those seem to be more $$ than the 600's which are more commonly found . as stated by larry above you may want to try at some point the AVS carb version . the edelbrock thunder series is an AVS carb ( 500 , 650 , 800 ) . more expensive new or used . added adjustability though should be a plus . if you look for a used AVS carter to rebuild be prepared for problems in the fuel bowl area due to old gas and especially old/new gas corrosion . plus sometimes old carbs are just plain worn out after being apart and reassembled several times .
I think 600cfm should work fine. Slightly leaner jets and get a power valve rated at half your idle vacuum if you had a Holley. Don't know much about the Edelbrock carbs. Larry's power timing thread is excellent too. Have any of you guys used the Summit carbs?
I have the edlebrock 1406 carb on my '66 300 with 4bbl and it runs really, really good. Mine is complete stock expect for duel exhaust. I had a miss last week and with some help figured out a plug wire was no good. Changed it and it's now running the best it ever has.
