Initial Tuning Suggestions?

[leeklm]

Quick background... Helping a friend with a 79 vette, which has a 350/auto, low compression 882/2.02 valve heads, headers, 3.73 gears, and had a B&M Blower sticking out of the hood with a Biggs 900cfm carb.  Car idled smooth, and ran generally well, but have no history of cam specs, CR, etc.  Car liked to overheat on the highway, which I attribute partially to the MSD not having a vacuum advance.  Since his wife wants to drive the car more regularly, we decided to sell the Blower and MSD ignition, and I rebuilt an HEI, qjet, and installed a 69 cast iron manifold.  We now have enough money left over for a new hood and having the hood painted!

I purchased the basic kit and new idle tubes from Cliff for carb #17058204, and did a basic rebuild, not changing the idle circuit other than the new tubes.036 if I recall correctly.  I installed 71 primary jets and .046 rods.

A couple of observations when tuning the engine now... when tuning the APT at cruise RPM (in park, no load), I am getting maximum vacuum at about 6.5 turns out, which seems a little much.  Would that indicate a larger primary jet should be installed?  Also, what secondary rod would be recommended in this combo?

Regarding ignition, I have full advance coming in about 2500 RPM, and set at about 38 degree full advance + another 10 degree with full vacuum.  For a street car, not seeing any track time, would you suggest connecting the advance to ported or full vacuum?

Thank you for any suggestions!  My buddy is not a "car guy" so I am trying to get this thing close without doing lots of trial & error, like i typically do with my GTO!!

[Cliff Ruggles]

Not so good news having 882 heads, they are pretty restrictive castings, but probably OK for what he's doing.

71 main jets are WAY too small for one of those carburetors, so it needs some attention there.  Which 46 rods, K, L, P, M, etc?

Without knowing the cam specs and static compression ratio it is difficult to make tuning recommendations, especially for the idle system.

I seldom use manifold vacuum to the advance, at least not for engines with well thought out components.  An efficient engine will not want or like a lot of timing at idle speed, and in most cases having to run a lot of timing at idle is just "crutching" not having enough fuel to the idle mixture screws or base timing too low.

Ya, I know all about the long/lengthy outdated reading on distributor tuning, I have to hear about it half a dozen times a week from poor souls who have lost all control of idle speed and the mixture screws because they are running manifold vacuum to the advance and 20 degrees, 30, or even more timing at idle speed.

Anyhow, when you get time, call the shop and I can supply a much better jet/primary/secondary metering rod combination, and PP spring for what you are doing.....Cliff

[leeklm]

Looking forward to the new parts Cliff.  Regarding the base gasket...  I am using an early chevy cast iron 4-hole manifold, which has the factory passage in between the secondary holes.  should a 4-hole base gasket be used here or an open gasket?

One last thing, this carb body has a lead/solder filled casting hole/plug next to the fuel inlet, facing forward, which is seeping a little fuel.  I presume this can be repaired similar to your procedure on the bottom casting plugs shown in your book.

What size drill bit and tap do you use on that front inlet plug?