For several years now I've been opening up a couple of Saturdays a month for custom tuning. Been having a great time with it and have met some really nice folks and had quite a few "troubled" carbs and entire vehicles brought here to custom tune.
I thought I'd start sharing a few of the stories as we get to see some pretty cool vehicles and a lot of different combinations. I'll not mention any names, just going to talk about the what I did to fix the issues.
Last Saturday had a later 70's Corvette driven here with a pretty "fresh" 383 stroker engine in it. It was topped with Pro Comp heads, about 10 to 1 compression and Comp XE256 cam. I know it's a pretty small cam for that engine combo but we were able to get it sorted out pretty good.
When it showed up I checked the timing and it was at 26 degrees initial, 52 total and another 11 from the vacuum advance for 63 degrees at cruise. The curve was pretty quick but not adding any timing at idle speed. With that much timing in it at idle backing the speed screw clear off it was still running WAY too fast at idle for my liking, probably around 850-900 rpms.
I moved the timing to 10 initial, which provided 36 total plus 11 VA for 47 at cruise. This dropped manifold vacuum at idle to about 18" and I could lower the idle speed to about 700rpm's, so good to go there.
I dove into the carb next, the owner had no idea who, what or when it was worked on last. It had a good NAPA blue pump in it but recent "soft" blue seal which was already swelled up and failing (sticking in the bore). The N/S assembly was the typical small windowed variety showing up in all the kits from the parts store and on-line sources.
The power piston hanger arms were purposely bend down about 3/8" and the tips of the 54K metering rods had been removed. Not quite sure what was up with all that but the jets were stamped #71 but drilled to just past .080". I scratched my head on that one for a few moments then moved on.
The carb had been converted to electric choke but the vacuum was still open to the choke housing so it was sucking dirty air thru the engine. Blocked that off, left the bypass air alone and ultra-sonic cleaned all the parts and started putting it back together. I installed 75 main jets and my full tapered 44 custom rods with .026 tips. Removed the plug from the airhorn for APT access and installed a 3/8 set screw in it. Installed a solid high-flow N/S assembly, new accl pump, orange PP spring, and new secondary spring. Replaced the CH rods with DA rods.
Since it was making PLENTY of vacuum at idle with only 10 degrees timing I left the idle tubes and DCR's stock, and all airbleeds idle and main at the stock sizes.
The choke pull-off had no restriction in it so I replaced it with one that I modified with a tiny hole" hole in the inlet for a clean/quick/smooth release to prevent hesitation/stumble/bog going quickly to full throttle.
....continued
