Hello fellow Chevy lovers! I'm new to this forum, and writing out of desperation after spending a week and barely making any progress. I recently purchased a '77 c30 with a dump bed added. After I purchased the truck and drove it home it began acting erratically so I decided to rebuild the carb. The problem is that it is a 77 Q-jet with pre-75 rods in it. I am trying to figure out what the correct primary metering rods are for this carb for an elevation of over 10,000 feet. After much searching and discussing the issue with various shops, nobody can seem to explain why. (I’m ONLY talking about primary rods here, because my problems have nothing to do with activating the secondary circuit). The s/n of the carb is 17056212 and the number 0977 stamped below, which I think is the production date. When I disassembled the carb, this is what I found: Primary circuit: .070 jets with .026-.031 rods. I’m not sure about the power piston spring because I lost it and ordered the Edelbrock spring kit with 4 springs, which are supposed to match the q-jet springs.
Thinking that somebody put the wrong rods in, I tried running the engine with (post-75) .052 primary’s, and the engine was starved for fuel, (as indicated that only a lot of pumping the accelerator would keep the engine running), and after opening the idle screws 3 ½ turns they had no effect. Since the only other post 75 rods aren’t that much smaller, I went back to (pre-75) .026/31 primary’s with .068 jets, and the engine is clearly flooded. I should emphasize that I live above 10,000’ and this normally requires smaller jet’s or larger rods to lessen the amount of fuel which compensates for less air. Next time I tried running .021-.045 rods in .070 jets, and I’m not sure what is happening; the idle seems fine, except that it changes speed slightly about every 20 seconds or so, and I’m hardly seeing any effect of the idle mixture screws. (Idle speed may have slowed slightly when they are screwed all the way in, but hard to tell with the idle changing all by itself). When I pulled the carb it seems like there was a lot of vapor in the manifold and raw gas on the gasket. The power piston spring did not release under acceleration, and the engine is having a hard time accelerating - it helps to pump the accelerator pump to get the engine to accelerate (which indicates it’s starved, but all other indications seem to be that it’s flooded).
I’m not sure exactly what the next step should be, but my main question is: does anybody know anything about what happened in 1975? If my research is correct, the stock primaries on a ’77 M4M Q-jet are .050 rods with .070 jets. However, I read somewhere that the normal difference should be around .03 between the rods and jets.
In addition, I'm having problems figuring out why the original gas tank, which isn't connected to the engine - keeps overflowing.
Any help is appreciated.
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