Did some mods to my bike this winter.
- Supertrapp 2-1
- Arlen Ness Big Sucker A/C
- "New" (used) CV carb
- Breather bolts for external ventilation

Started bike up yesterday with 12 discs in the Supertrapp. Ran like crap and threw out lots of black smoke from exhaust. Took jets out, turns out mainjet was 200. Don't know slowjet size since I destroyed it while trying to get it out. So I put in 180 and 45 jets today. Also put in 4 more discs, so 16 in total. Now it seems to run lean. Won't start without choke, just backfires through carb. Starts and runs with choke though, but not that well. When I turn the choke off while bikes is running it runs OK on idle, but 1/4 to about 3/4 throttle it backfires through carb and wants to shut down. But when I open full throttle it's OK. Tried turning the Air-mixture screw half a turn in, and that worked well. Improved throttleresponse and no more backfiring through carb. Air-mixture screw was about 1 1/4 turns out as stock when I removed the sealing. After turning it 1/2 turn in it sits about 3/4 turns out in total. So.. Does this mean that I should try a 48 slowjet?

 

Ok. What year and model bike and how many miles? AND.. How long have you owned it?

Why did you replace the carb?

On the Supertrapp, you running an open or closed end cap?

What Mods have been done to the motor?

With a 200 main and who knows what the slow jet is, one would think there was mods to the engine...

Normally if you have to keep turning the idle mixture screw in to get it run right then your slow jet is too big. So going to a 48 might be a mistake.

 

This sounds all too familiar on this forum.
Turns out timing slways needs to be sorted out first. But first...