Observation/question regarding K&B Sportster Engines

[flawedexistence]

:?

I have both a .45 and .65 Sportster engine. These date from the early 1990's and are the latest models. I've had a heck of a time getting either to run properly. This includes difficult starting, cutting out, poor idle, etc., etc.
In fact, I couldn't keep the .65 running at all. I should mention that I'm an experienced R/C flyer and instructor. Recently after not running either engine for nearly ten (!) years, I got them out and decided to bench run them one more time. UGH! Same results.
I then tried running the .65 without the muffler............big difference! Nice power and transition and decent idle. Now what? Well, I disassembled both mufflers and removed the baffles. Both run great now; are a bit loud, but not annoying.
Has anybody else observed this quirk? If so did you solve it in another way? It seems to be too much of a coincidence that two engines of the same type should exhibit this problem. Anybody have any ideas on this one?

[Atomic]

Hola. :P
when i used to fly alot years ago i ran tons of K&B engines.. they werent the most powerful out there.. but man when you got them settled in and mixed right they ran every time.
anyway.. many of them were the sportster models, and i can tell you from experience that i removed the baffle from each and every one of mine. it was nothing but trouble.. way too much back pressure for the engine.
in fact.. one of the only complaints ive ever had with K&B engines was the muffler on the sportster series.. if the bolt threads werent stripping out, then the baffle was giving some kind of grief.

for being a one needle carb though, that thing was pretty solid.

-Joe

[joebugs1]

I read this thread, went home, pulled the baffle out of one of my .65 Sportster mufflers, cranked up the engine, and in about 1.5 seconds blew the back half of my freakin muffler right off. Lucky nothing was behind it, 'cause it came off pretty hard and fast.
And to think it was running fine with the baffle in...l
So I'll be buying new parts for a couple Sportster mufflers; last week I torqued the end nut too hard and pulled the bolt off the front endcap.
Be careful with these things