I bought a second BST40 carb from a local DR member so I could do the "BST Magic" to it and maintain my perfectly running stock carb. To my surprise, when I opened up the carb I bought, it already had a jet kit installed and had a tapered needle with a drilled slide. So the heavy lifting was already done, now I need to tune it. My bike came stock with this swiss cheese airbox door. So, with the original carb, I made a plastic plate to cover all of the holes because the carb was 100% stock. With the blocked door and the snorkel removed, the bike ran great with only a little hesitation off idle, but no surging or anything out of the ordinary.
Now skip ahead to installing the carb with all of the modifications. I swapped the components I wanted from the modified carb over to my stock carb. I had no written instructions, but I have seen plenty of videos to do the mods.
-Tapered needle with clip on the 4th position and a small washer under the clip.
-150 main jet (I don't know what brand)
-adjustable fuel screw
Here are the things I have done to the bike/were already done to the bike:
Airbox snorkel removed
Header pipe weld ground down
Twin air filter
Uni secondary breather filter
fuel screw out 1.5 turns
Components listed above were swapped in to the carb after being cleaned.
Blocking plate on the swiss cheese air box door removed
The bike idles fine, just as it did with the stock components. It seems to run fine too, but I have noticed two distinct new "features" of this new set up.
1) The bike is a lot louder on acceleration (almost like putting a cold air intake kit on a 4 cylinder) I am assuming this is due to the swiss cheese design on the air box door now being open.
2) The bike pops on decel, almost as if I were shooting a cap gun at about 3-4 rounds per second. (pop, pop, pop.......pop, pop, pop)
Now the help I need:
1) Who is the manufacturer of the jet kit I have based on the pictures?
2) How do I get the distinct popping on decel to go away?
3) Should I put the backing plate back on to block all of these holes and drill a 2" hole in the top of the airbox instead?
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