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I began using R/C throttled engines long before "muffler pressure" was invented. The only reason it is "needed" today is because the manufacturers have increased the carb's flow rate to the point that they need help from somewhere. Muffler pressure is used as that somewhere, but not always successfully.

Back before muffler pressure, air bleed carbs worked much better than today. Even very high quality and expensive engines utilized air bleed carbs successfully, for the most part.

Today I frown when I see someone adding muffler pressure to a K&B Sportster engine. They are asking for trouble. We modelers love to enhance our engines using our own ingenuity whenever we can. Especially if it is as easy as drilling a hole, tapping said hole and then screwing in a pressure nipple. Unfortunately, what most folks do not realize is that in spite of its looks, the Sportster series is a rather high tech product. The mufflers are actually tuned to provide a boost over open stack running power figures and they are also one of the quietest factory stock mufflers that you will find. The Sportsters carbs are metered and throated to provide the perfect amount of suction for good fuel delivery. Adding muffler pressure throws the Sportster carb out of calibration. Depending upon manufacturing variations, you may, or may not, be able to tune the carb satisfactorily when using muffler pressure. I remember when these features were new and "leading edge". Today, newbies come along and assume that these engines are low tech garbage and modify them willy-nilly. Then use their unsatisfactory results to reaffirm their original suspicions of low quality/low tech. Sometimes it is difficult not to say something. After all, I no longer have access to the magazine articles that would back up what I would tell them. They would just see some old timer that they think is trying to defend an old product that they happen to like. I used to be arrogant like that too...<G>


Ed Cregger