[George Snyder]

David,

A few suggestions.

To check a blown power valve is easy. With the engine ideling hold your fingers over both air tubes. If the engine shuts down it is blown. You only have a power valve on the primaries. If blown when you replace it try getting one that is 2 inches lower than your intake vacuum, rather than the standard 6.5. If your jetting seems right, but the exhaust still reeks with gas smell this may help.
To help with the backfire and sputtering during acceleration, try setting your indle more from the rear screw than the front. You will see the throttle plates opened slightly.

The timing I agree with others. Blue bushing (21) + 14 initial. Try light silver springs first and adjust from there. Remember that you can mix and match any spring combination. All in by 3000 sounds good.
Jetting can be tough, eight sizes seems to be the normal, but I have seem good results both closer and farther apart.


Good luck.
You did not mention which intake you are using? If it is an Edelbrock Performer RPM, make sure you have a steel carb plate installed between the intake and carb. They are known to be hard to seal.
Did you change the carburetor gasket each time you removed and reinstalled the carb? You may be able to flip them over one time.