Hey, jeffreykogan.... Here's my madness to the method:
My logic goes like this. I view the TAV2 as a variable jackshaft with a starting ratio of 2.68>1, and if Engine HP permits, an ending ratio of 1>1.
So, in the case of your bike, your starting ratio is (overall) 11.79>1. At that ratio, the TAV2 will max out at about 3500rpm/23mph, and it will then start advancing the ratio, (sort of like upshifting) until the engine can't handle the advancing without an RPM drop. IF you were to have Plenty-O-Power, it would advance all the way to a 1>1 ratio, driving your 44T sprocket, for an overall ratio of 4.4>1. Even at 3500 rpm, that's 61 MPH!
As you can see, you are potentially WAY over-geared for a 3hp engine. My experience with slapping a 3hp Briggs on the back of a mountain bike got me into the 33-35mph range on flat ground. (I'm beginning to think B/S under-rated their motors because the difference between a 80000 series 3hp Briggs and my Lifan 2.8hp feels like a LOT more than 1/5th of a HP!)
Soooooooo!.... (Yes, I'll get to The Point, I promise! )... If you were to slap a 54T sprocket on the rear wheel (pretty easy to find), your TAV2 set-up would give you a starting ratio of 14.47>1 (3500rpm/18mph).... it will then advance to a potential of 5.4>1 (3500rpm/50mph).
Even the 54T is really too small, but I know finding anything larger is kind of tough. I have a 60T on mine, and it looks like a surplus blade from a local sawmill!
If it was a perfect world, where we could easily obtain the "ideal ratio" for our set up (TAV2 w/ 3hp engine), it would put us at 3600 rpm at 30-35 mph.
IDEALLY... it would be our little 3hp engines/ TAV2 geared to a 85T sprocket! That would net you 3600rpm/32mph when the TAV2 advanced all the way to 1>1.
What I'm getting at is, through trial and error, we all kinda know that an honest 3hp can get us to 30 mph-ish. Even with a 85T sprocket and your TAV2, you're in no danger of over-revving at your potential top-speed of 30 mph-ish.
I need to explain why I use 3500rpm as the TAV2 "max" rpm.... With the stock spring on the driver left untouched, the TAV2 will let the engine rev up to about 3500 rpm, and then if the vehicle keeps picking up speed, the belt will advance, keeping the engine at very close to the same rpm the whole way. Unless you have a LOT of HP, it's hard to get it to max the ratio AND go higher than 3500 rpm. Yes, you could travel down a very long steep hill but that's almost what it would take.
One of things I would like to experiment with is the three hole positions on the TAV2 driven spring. Supposedly, you can set it up so that the "hold or shift rpm" will be higher than 3500 rpm. I have never heard any ACTUAL rpm #s gained by doing this, though. Also, tighter springs for the driven pulley are available to accomplish the same thing- letting the engine rev up a little higher before the TAV2 starts clamping down on it.
Many of the members here (too many to quote) have warned that the TAV2 is just a bit too much for anything under 5hp, and I would have to agree from a top-speed standpoint. I still think it's workable as far as having great take-off speed, but if you're seeking ultimate top speed, a centrifugal clutch driving at the proper final ratio is the way to go. I'm sticking with my TAV2, because with the little Lifan, it's good enough for what I'm doing.
Regarding your question on the carb, I think if you're after better performance, I would start at the exhaust.
There was a fascinating article that I found on another forum, about getting more hp from a flathead 5hp B/S. They dyno-ed it stock and then step-by step modified the motor, testing the results after each mod.
One of the biggest (and easiest gains) was axing the stock exhaust and going with a less-restrictive one. Gains were realized EVEN WITHOUT GOING ABOVE THE STOCK 3600 RPM! Let that sink in! So if I were to go after more performance from the Predator 79, I would start with governor removal, a header with less restrictive muffler and then a tunable carb for it. (If you get that NT carb, it'll eliminate the governor anyway!)
Geez, my typing fingers are tired. If I find that article, Ill try to post it as a PDF.
My Butt-Dyno speaks volumes, though.)
