BS200 jetting etc.

[BRT-GTR]

        Got to ask ---- Did Mikuni use a revised numbering system on the later carbs  for mains, pilots, needles etc.

  Also found these on the UK Mikuni site  -  UFO inserts.  Not available for 26mm carbs  (yet?) but look pretty simple.  Just smooths out the bottom of the carb slide and  cuts turbulence with significant performance benefits ??    Might interest Rod (Husker) and others including me  .

    http://www.motocarb.com/ufo-insert.html                                                          Brian.

[OldSwartout]

       UFO inserts.  Not available for 26mm carbs  (yet?) but look pretty simple.  Just smooths out the bottom of the carb slide and  cuts turbulence with significant performance benefits ??    Might interest Rod (Husker) and others including me  .

Don't do it! They completely screw up the whole jetting system.  It can be fixed with different main jet, idle jet, needle jet, and needle.  Just count on many hours of trial and error to get the job done.

It's really not quite that bad, but it will take a few new parts and quite a bit of time to get it right.

My brother put those in his CB350 just before Daytona one year, bad mistake.

[BRT-GTR]

     Thanks Karl, the message is clear.  Did your brother ever sort the CB ?

  Even so, as a gas flow engineer, I can see the logic. Could effectively simulate the fitting of a bigger carb !! with increased air and fuel flow, at very little expense and no engine modification. Maybe when I've got a spare GTR running and time to play, I'll give it a try. Our buried carbs won't help.                  Brian

[OldSwartout]

He did get it mostly sorted after another race weekend or so and they may have helped a bit. He never had dyno data. He had a very aggressive camshaft that caused some valve spring problems which didn't help matters any. Trying to jet the bike with broken valve springs didn't work well.  He did have the fastest CB350 in AHRMA for a while.

The UFO inserts do sound like a good idea. The smoother flow across the needle and jet seemed to change the jetting characteristics significantly, and not proportionally across the full range, so everything had to change.  The idle and low to mid opening curves apparently change quite a bit.  Trying to get idle, low throttle and roll-on correct was the biggest problem.  They've been around long enough that there may be more data on what specific changes should be used to start with.  He was trying them in 2002/2003?, not long after they came out.

[BRT-GTR]

           2003?  Didn't come across them until now, maybe not quite the 'magic bullet' they had hoped for. Bit like the Wal Phillips fuel injector from the 60's but worth further consideration.                                  Brian.

[OldSwartout]

Speaking of fuel injection, I think someone that has a decent understanding of the electronics involved could adapt a couple of the units from modern dirt bikes to an old 60's/70's bike.  The dirt bike ones don't need much power, some even work just from kickstarter speed generating enough electrical power for initial startup, so they don't need a battery.