There is something not right, RPM's have nothing to do with this, only temperature, you should be able to remove the spring completely and the weight will just sit there in the down position. The flapper in the normal operating position (weight down) directs the exhaust down as you say, with weight UP, (engine cold) the flapper just makes the exhaust go up and over, forcing a more intimate contact with the bottom of the intake. Since I have an exhaust just sitting in the garage, I should post some pictures on the tech tips on where the stuff is oriented under which conditions, as this comes up all the time. Only thing is I need to have my wife help me with the postings....except for a brief period, I haven't had a spring on mine ever, in 30 years, and noticed no consequences at all, and it has been in some really cold situations. I didn't even know what it was for or what it did until about 2 years ago when it was running roughly (never did figure out what happened, it just started running well again) That is when I studied it a bit. Got a new spring, but there was a chunk of the old one stuck in the flapper shaft, and I only tried it for a while and it made no difference that I could tell, just frustrated me. But to answer your question, I am pretty sure it shouldn't be doing anything in relation to RPM's. We will have to wait for Dave for a more definitive answer. I do know if it opens up after it is warm it will make the engine run really, really bad.
