evening guys,

I have a 72 Skylark, 350 with a rebuilt 2barrel rochester (rebuilt by holly). The motor runs ok and looks pretty good for the origional, valve covers are clean, heads look fantastic and compression test at garage was all within parameters.

The issue I have started when I over heated a few weeks ago. Now I have an entirely new cooling system (stayed with stock) as well as plugs wires, cap, rotor and coil.

The problem now is I cannot dial in the engine to run correctly (read smooth and efficient). I tried the local garage for tuning it in and they did just that, but I ended up riding a rocket - about 6.5 mpg and the thing took off like a bat out of hell. Thats all great but not really what I wanted. Before things went south with the heating, I was geting 15-16 mpg but that was with the timing so one sided that the distributer was turned as far as it would go counter-clockwise with the idle set very very low.

now my first question is what am I going to do to my baby if I put the timing back the way it was before it over-heated?

Second question is how far out from seated is an ok needle set point, right now I have my adjustment needles on the carb at 3/4 turns out from seated, any more and I start to blow carbon - BIG TIME (could this be a sign of bad floats??)

Overall question is where do I start? adjust timing, adjust carb???

Thanks in advance for any help or advice you can give me.

Set your timing first. Bring the engine up to top dead center, TDC on your timing mark. Now note where the rotor in the distributor points. If it is not close to lining up with #1 plug contact, rotate the distributor until it lines up. If it's about 180 degrees off, rotate the engine one more revolution as you are on the exhaust cycle, not the firing cycle. If you can't get the rotor and plug contact aligned, you need to move the plug wires one hole in whichever direction will bring you into alignment. When everything lines up, start the engine and use a timing light to set the timing to factory spec. Now when the engine is warm and the choke is fully off, turn the idle mixture screw IN until the engine starts to stumble, then turn it out about a quarter of a turn. Now do the other mixture screw the same way. It may take a couple of tries to get it spot on. When the engine is warm and idling smoothly, open the throttle as quickly as you can. If the engine revs quickly without stumble, leave it alone. If the engine hesitates, try advancing the timing a little at a time and try opening the throttle again. Only advance the throttle until the hesitation is gone. Shut the engine off. Let sit a moment and start. If it still starts easily with no kick-back you're good to go. :hurray:

thanks for the info njlimbaugh.

My problem with the idle misture screws is that I have to turn one side in and then the other before it starts to stumble which also makes me wonder if the floats could be mis-set or sticking, or is that because the sides are not seperated in the intake manifold???

All 2-barrel carbs will react the same way because, in effect, one barrel feeds one half of the engine, the other barrel feeds the other half. Like I said above, work one screw then the other: in until the engine stumbles, out until it smooths out; usually one-quarter turn or so. Then work the other one the same way. Don't forget, those screws only adjust idle mixture, usually only up to something below 1000 RPM. The high speed jets are fixed and do what they do regardless of the idle mixture settings. :waving:

It sounds like it's idling on the main discharge. The float is probably okay. You could check it's setting but if the carb was not messed with it should not have changed. I don't know if you have the skills to address this issue but I will try to explain how to check for this condition and fix it. How I would do it is to look down the carb with the engine running at idle. You may need a light. Look and see if you see any fuel coming out of the boosters in the middle of the venturi's. If you do the engine is getting fuel from the main system and not just the idle system like it should. Ideally you should not see any fuel anywhere at idle when you are looking down the carb. What you need to do is to shut the throttle blades further at idle. To do this you have to advance the timing, which generaly increases the idle speed, and then adjust the idle speed back down with the screw on the carb linkage arm. You need a good timing light and make sure the vaccum advance hose is off the distributor and plugged to prevent a vaccum leak. Do not advance it a crazy amount past what the factory calls for or it will ping like hell. At this time also make sure the vaccum advance is working properly in the distributor. If you don't know how to do this, ask. Advance the timing a little at a time and bring the idle speed down accordingly and keep rechecking down the carb throats to see if fuel is still coming out the main discharges. When you can no longer see any fuel coming out you should be idleing on just the idle circuit. Then you can adjust the idle mixture screws like normal. At this point I would tighten down the distributor, recheck the timing to make sure it didn't move and then test drive the car. IF it operates okay with no pinging and decent performance I would drive it awhile and see if you are satisfied. Come to think of it while I am typing this, this could be a ported vs. open vacuum issue to the vacuum advance on the distributor. Your carburetor probably has more than one place to hook up the vacuum advance hose to the distributor. One above the throttle blades and one below. The one above the blades is a ported vacuum source that does not see vacuum all the time, mostly under part throttle cruising, and one in the base that sees manifold vacuum, vaccum almost all the time. If you are using ported vacuum you will need to set the carb to idle faster which may cause the problem you are having. Plugging the distributor into manifold vacuum will cause the idle speed to go up on it's own because you are now running full advance at idle and you can adjust the carb screw back down. So my revised suggestion would be to start the car, unhook and plug the vacuum advance from the distributor, set the timing to the factory spec, hook up the vacuum advance to manifold vaccum and see where the idle speed is and adjust it down to where you want it and see if it is still dumping out the main discharge. If it is try my earlier suggestions if it isn't drive it for awhile and see how it works out. If you cannot get it to run without dumping from the main discharge no matter what you do then the carb is the problem. There are modifications that can be made but that is not a job for an amature. You will probably get all kinds of opinions on running full advance at idle, most old timers don't believe in it and wouldn't hear of it, but it works damn fine. I've logged hundreds of thousands of miles behind various Buick V8's and every one of them was running full advance at idle. Give my suggestions a shot and see what happens. Good Luck and let us know what happens.