I persoanlly are quiet fond of the Force engines, the carbs and general quality of the engine is very high for its class(low budget sport engine), the .21BB used by HPI is a cross between a Force p4 and a Delta force p8... I just happen to own a Delta and I started mixing and matching(the delta was stripped down at the time I disassembled the .21BB to have a peak). For me the modification was practiacally free(already had servicable parts), so I did and I`m very happy with the result...I am however using the 8mm Delta carby and 8 port Delta P&S... I believe I`m getting around 2.5hp and close to 40K RPM out of my hybrid, porting really brought the throttle response to the party
I guess if you or I wanted to buy the Delta parts to use it would come out close to the price of a 8 port Hyper NIB or somthing like that, the Delta I believe is a better engine and the 2 put out simular power...which then of course could be tweaked further with porting.
In your position I go for the "whats there to lose" attitude, port the .21BB as it is, disassemble and drill the carby to 8mm and if all goes well you`ll get a MAJOR increase in performance... for nix`s. And then if your still not happy just buy that new mill you wanted
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I port all my engines...if not a full blow port just a little cleanup/de-burr, it does make a difference to any motor for the better(unless you slip with the dremel..
), last I checked in Australia the Force 8 port parts were pretty resonable priced...where you are it may be a different story, if you want I can give you all the relavent part numbers
Hope this helps, and makes sense(that cocktail party last night was killer !! )
Cheers
TM