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One aspect of the mechanical pump not mentioned yet is that it can fail slowly with an imperceptible effect that only shows on the high end. I ran the original mechanical pump for years and chased performance on my truck as I was using it on the freeway as my DD. I went through the usual carb swaps, 8:1 head, cam swap etc. but in the end it was only when I was perduaded to swap to a 'lecky pump by Yorker matched with a Rochester carb that I found that I could run at 65mph on 32' rubber witout an overdrive and 75mph with. The old pump was putting fuel through but not enough to feed the old lump at full chat. THis gradually got worse until she finally stopped completely on the trail one day resulting in a tow out froma friends Jeep.
For those with performace that won't exceed 55mph this is something to check.
For those with performace that won't exceed 55mph this is something to check.
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