My recent motor change has lead me to issues with setting the timing to properly dial the carb. For starters I'm using a stock gm points distributor rebuilt with 0.017 points gap "dwell"... I changed my carberuator from a 600rochester quadrajet (where the engine would only run properly at wide open throttle) to a holley spread bore 650 double pumper that I robbed from my camaro (very similar motor build) to problem solve my truck... If I try to run my base timing at 12 degrees with the vaccume advance line plugged into the base of my holley so the vaccume advance is operating the engine will only run properly while at low throttle and surges something fierce when at top end or kick down. however if I disconnect my vaccume line and set my base timing to 16degrees, the engine seems to run fine (but still not perfect). Is this a case of poor vaccume advance cannister or manifold vaccume pressure problem or more a carburator problem (either too small of jets in my metering block or too small primary "squirter"???? the engine won't even run properly enough to open up my secondaries Jet sizing unknown at this point but primary squirter is #25 while secondary squirter is #37. FYI-I'm replacing my intake with a performer rpm air gap and my carb with a holley square bore 650 double pumper later this week but I need to have better idea of whats happening before I spend another grand on my engine.
I have figured out that my problem lies with my carburator jetting. Last night I played with my primary jets and found the low end throttle response was best with 68 primary jets (8 sizes larger than stock) with a 25 primary squirter. Tonight I will play with my secondary jetting (stock is 83) so I"m going to try about 85 or 86 as a base point with a 37 squirter. As for timing, I find the engine likes to run with the 16 degrees initial and approx 36 degrees at WOT. The engine takes the advance without running on or being hard to start... this is sort of a race car set up at the moment so I would like to get my vaccume advance working properly to help with better fuel mileage. ANY IDEAS on the vaccume advance? If I change my timing I will need to play with my jetting again.
