Scott,
I don’t know how long you have been running the Rotax, so don’t be offended if you already know this.
All good advise you’ve received on this thread. One of the biggest things new Rotax drivers need to adjust to is, not letting the slide close all the way. You don’t have to power brake the hell out of it, just keep the slide lifted enough for the brakes to be effective. If you do let the slide slam shut, the carb goes back to the idle circuit and takes time to create venturi vacuum causing a delay or as some call it “a bog”. Also, don’t just jamb it coming out of a corner, just give it what it can take and ease into it.
A 152 jet does not sound that bad. The Rotax seems to like fuel anyway. There is inconsistency between the different engines and carbs. Our first Rotax would require a 148 jet when everyone else seemed to run a 155. Last years motor never saw a jet leaner than 155 in competition. (qualifying is a little different) If you lean it to where it gives you an occasional (one a lap or so) pop, you’ll probably be ok. We found we could go lean and be fast for the first handful of laps then it would start to lose some power. It’s a trade odd for sure. The Rotax has a pretty small radiator and a pretty big carb. Possibly check your float level if you haven’t done so yet. And keep the carb clean. We also had problems last year using the Rotax legal fuel filter. Our problems sound somewhat consistent to what you are experiencing on top. The filter element media seems to be breaking down and getting inside the carb.
Roman ran a 12-80 gear at the Rotax Grands, (clockwise) and had a trap speed of 79 mph at the braking zone going into one. (mid 56 second laps) Gearing is always some kind of compromise. At The Track in a Rotax it seems the hairpin is the corner to concentrate on, if you can’t get off of the hairpin, it’s going to be tough to generate good lap times.
Also, as has been mentioned numerous times, battery charge has an impact on the motor being able to rev as well as the exhaust packing baffle. Stick a flashlight in the end of the pipe and make sure there are no breaks in the perforated tube you wrap the packing around.
Be religious about cleaning your power valve and carb is the best practice.
Rick