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I recently had a little trouble with my truck running excessively rich all of a sudden. I found the power valve had come loose on the 2150 (2bbl) carb. The power valve is located on the bottom of the carb, between the idle mixture screws, inside the cover shown in the middle of this picture:
I tried to reinstall the power valve, but the threads would barely catch. After some serious headscratching, I found some variations in the length of power valves from different manufacturers. Here is the critical dimension X, from the ends of the threads to the gasket surface:
Here's the removed power valve, showing the shorter .4155" dimension:
Here's the longer version, at .4920":
The difference is only .076", but it made all the difference. Sorry, I don't have records for which manufacturer made which version. But if you have to replace one, measure it first to avoid the short version. Avoid a thick gasket, too, for maximum thread engagement.
