My son recently bought a 1977 with a 402 BB in it, it looks like the previous owner just raced it..
The interior needs to be replaced but the body and engine is in great condition. My question is supposedly it has a 750 CFM Holley carb on it right now and to me it looks like it is running rich, i kn ow i need to get the block size and carb #'s this weekend, but does anyone have any suggestions about putting a smaller CFM carb on this size engine or just adjust the carb that is on their and is there any other sensors that would need to be changed out if it is running rich ?

 

First thing is take out the spark plugs to confirm the rich condition. This will also give you an idea of the condition of the plugs themselves. If you just bought the car, it is a good idea to give it a complete tuneup before attempting to tune the carb. New plugs, check the distributor cap and rotor for carbon tracking or burns (replace if needed) and check the timing. A weak ignition system or retarded timing can make an engine seem rich.

One quick check you can do is check the float levels, that may help some. If you are not sure of the condition of the carb, you might consider getting a kit and going through it. A rich mixture on Holley carbs can be a number of different things. If the previous owner tried switching jets you may have a set in the carb that is too big. Depending on what you want to do with the car (race?) it could be in your best interest to get a jet assortment. You can get them from just about any auto parts store for around $40. Through trial and error (and reading spark plugs) you will get to the correct mixture. Also, Holley carbs have a known weakness to backfire. Power valves can get damaged if the engine backfires thrugh the carb and this could add to your rich condition.

Without knowing what mods have been done to engine I'll guess that you could put a 600 cfm on the car. You'll probably still want to get the jet assortment though if you do as it will need some tuning.

 

+1 to what JRs72RS posted

Most likely if he only raced it the timing is set to 32-38 deg base DDC and the advances are removed. You need to get all that stuff sorted out before you declare a Carb issue. But again if it is setup for racing they normally give up "drivablity" for speed. So your carb is all jetted wrong for normal street driving. Another thing is if the car has been sitting the carb gets varnish in it so you may want to push some cleaner thru it before you adjusting anything.

Depending on the RPM rangeyou want to run in a 750 is about right maybe a little on the big side.If it is a little bit bigger then it needs to be it should not cause a rich issue. If you had a 850 and you said it was bogging or had flat spots I would say you where over carbed.

If you get to the point you want to change the carb and you do not want a ton of hours playing with it to get it rightyou should get the Holley Avenger. They are design to get you 95% there right out of the box. Its up to you if you want to fight for the last 5% or not. I didn't turn a single adjustment on mine,,, They have 670 and 770's. Either would be fine for the 402. Lets keep that no adjustments between us, if anyone asks I spent days tweaking my carb.

 

thanks for the carb advice, it sounds like i just might do that.. Now the next problem, i replaced the starter since evidently it busted, the previous owner just had a push start button on it since the ignition switch is broken, i have one on order.. I have tried to jump it and i am off to get some bigger jumper cables to make sure the ones i have were not the problem. Since replacing the starter it doesnt crank the engine enough, would it be smarter to get a heavy duty starter and alternator, i replaced the ignition coil pack cleaned the cap and replaced the plugs, i was also thinking of buying a new ignition wiring set since it looks like the previous guy re ran some of his own wiring for that push button...

 

A new starter should turn the motor, but that depends. Not enough info to be certain. A stout big block will need more than a stock one. If you are replacing it I would just buy a high torque and be done with it. Alternator??? If the one you have is bad OK but there is nothing to gain in cranking dept. by getting a new one, a strong battery is a better purchase.

You replaced the coil, is this an HEI dist? Was the coil dead? Did you put insulating grease on the washer between the coil and cap? Also, you say that you cleaned the dist cap, that is not good. Carbon tracking can be cleaned but it will always come back. If there is corrosion evident on the terminals inside, replace it along with the rotor. I have seen many HEI dist burn cap or rotor or both because of a mis-matched set. Always get cap & rotor as a set from the same manufacturer.