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Crockett's BK Carb Mod

Posted: Sun May 22, 2016 7:05 pm
by 4Strokes
Others have documented and reported this modification. This is Rob's version of the BK Carburetor Mod. This modification is intended to limit the fuel squirt from the carburetor accelerator pump into the engine for an increase in performance and fuel efficiency. The mod itself only takes a few minutes.

With my carburetor, the squirt previously continued for about 2.3 seconds when I hammered the throttle open, and now with the mod it is about 1 second. There is a metal tab where this modification is done, making it look like a adjustment screw was designed to be located here.
Drill the metal tab
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Tap the metal tab
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Insert spring and screw
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If you use a drill to drive the tap, be aware that you need to back it in and out while advancing a little each time--otherwise the tap could get jammed in the hole. I used a 6-32 tap and drill set because I already had one, and a 6-32 x 5/8" stainless machine screw from my local hardware store.
Trim the plastic shroud
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Crockett BK Mod Complete
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I forgot about the plastic cover and trimmed the length of the screw down--it was almost too short. The original 5/8" length of the screw would have been just right. I snipped a piece of spring from a ball point pen to use, and squirted a little Locktite on the screw to hold it in place. The black plastic cover needed to be notched, and I used a round file and an Exacto knife to do it (the cover has a flat surface ready for just such a cut-out).

Hardest part of this mod? Removing and re-installing the carburetor by far. Measuring the fuel squirt time is a little tough to coordinate, with one hand on the throttle, the other holding up the carb with the rag over the barrel (it squirts a fair amount of fuel) and holding the stop watch.