2 barrel carb tuning

[rjason]

I am having trouble with poor throttle response and sluggish acceleration in my '64 LeSabre. It has the stock 300ci and 2 barrel Rochester. I have replaced points and condensor as well as plugs, wires, cap, and rotor. I have the timing dialed in, but it still feels sluggish. I realize the 300 with a 2 bbl in a big car is no hot rod, and i have no desire to drive it as such, but i don't think it should have THIS much hesitation?!

Can someone give me the basic rundown for the tuning/adjustment procedure on this Rochester carb? What is a good initial starting point for the mixture screws? Is there an idle adjustment other than the screw on the throttle arm?

I have searched the forums for tuning info on my engine combo without much luck. Thanks in advance for any help or suggestions.

Jason

[Jim Carmichael]

One thing to check on is the exhaust. Some of these early Buicks used a double pipe and the inside layer will rust through, then exhaust pressure will collapse it onto the outside layer blocking the pipe.

If it sounds like it's being strangled that could be it.

To test for this condition hook up a vacuum gauge and run the engine at a steady speed around 1500 / 2000 RPM. The gauge should stay steady and if starts to drop you know the exhaust is plugged.

Idle adjustment on the carb won't really make much difference in power.

[rjason]

Thanks for the quick response, Jim.

It's not that the car seems to be lacking power so much as there seems to be an unusually long delay between opening the throttle and the engine actually reving up. Make sense? Initially, when I got the car, it seemed to be running a little rich, but it ran well and the delay in throttle response I mentioned wasn't there. I tried to do a little adjusting to get the mixture right and after that is when i encountered the issues I am having now.

It is for that reason I believe I need to better tweak the carb to get it to where it needs to be. I mentioned the idle screw on the arm only to ask if there is another means of setting the idle once the mixture is correct, such as an air idle bypass screw?

This is my first experience with tuning this type of carburetor (in case it wasn't already obvious). I was hoping someone might be able to give me a quick play-by-play. (i.e. turn the two mixture screws all the way in, then turn them out 1 1/2 turns, adjust this screw in/out so much then ...) So far I have just been winging it with my hand held tach and/or vac. gauge, but need a little imput on a good starting point and what kind of readings I should be looking for. Also some order of steps to take, start to finish.

Thanks again.

[rjason]

By the way, is this the best area for me to be asking this question? I wasn't sure if I should post it here or in the "300, 340" section or the "1960's" section?

Newbies! Am I right?!

[Jim Carmichael]

I always start by turning the idle mixture screws all the way in until they are lightly seated then back them out 1 1/2 turns. Next set the idle and let it warm up to normal operating temp. back each screw out or turn in to find the fastest idle and if it goes up bring it back to the specified speed. this wil provide a rough setting but to fine tune it you need to slowly turn the screws in one at a time until you see a 50 RPM drop in idle speed, then turn it back out 1/2 turn. Do this to each idle screw adjusting the idle speed back to specs as needed.

As far as your hesitation goes it may be that your accelerator pump is not working. With the engine shut off look down the carburetor and open the throttle and you should see a stream of fuel. Also make sure your vacuum advance lines were not left off as this can cause a hesitation.

[rjason]

Thank you again, Jim! That is exactly what I was looking for. Already confirmed that the vac. advance is hooked up and working, and the accelerator pump is working. I am headed outside to tune using your tips now.

Jason