Yes LS614 is right on about the expansion chamber or just a good free flowing exhaust period, it make no difference what you are putting into the engine if you cant get it out just as good so it can breath properly, you may even try a # 74 bit and just play with the needle to find that sweet spot, my engine 4 stroke just a bit unless under a slight load, I know some say they have zero 4stroking and that might be true, but I have had mine in the NO 4 Stroking Zone as well and they ran to hot and thus to lean so I richened them back up a bit, I ride 7-8 miles at WOT sometimes and if an engine is running lean it will cook down running like that so I dont mind the slight braaaaaaap at low speed and no load, I still get 41mph WOT with no wind, very flat ground on a good day and 36-38 mph at will wit a very comfortable cruise speed of 30-32mph with no 45 stroking at this speed.
I have manic intakes on mine and free flowing exhaust, the exhaust makes the biggest difference of all on these engines in my experience when it comes to instant noticable improvement in the way they run and pull hills.
Good luck and get a better exhaust asap and then along with the carb. tuning you will see a nice difference..........
without higher compression and a very good exhaust, I cant see the 18mm Mikuni carb doing very well on these engines, you will need to mix a good bit of fuel with that volume of air flow that 18mm will give you which may just be a bit much for the china girl, some fellas have got 45+mph using a well tuned NT carb. and a few other goodies, but I have been wrong a gillion times before too! so I say give it a shot and let us know what you nd up with.....
Originally Posted by Don P
i agree with you that the expansion chamber is needed to smooth this thing out. but it will be a week or two before i can get one low on FRN Federal Reserve Notes.