5 mph more top end would be great on my 257cc (260) Linhai  By  4950cycle (Read 7,148 times)

A low compression engine can use low grade fuel however the Yamaha is a mid to high compression design if memory serves correctly and in the absence of a fuel injection system with knock sensors you should always use mid grade to premium to minimize the stress on the valves. Even the slightest amount of early detonation even if it does not ping excessively has the potential to heat up the valves more than normal leading to excessive wear so that they can require more frequent adjustment.

JCL MP250A Lihai 257cc powered Its running fine now. The 12 gram DP style sliders are 2 grams per slider less than my stock rollers were. But instead of increasing RPM per speed / mph my RPM decreased ? I was going 67-68 mph with my old 14 gram "rollers" with 6600-6800 rpm . Now with 12 gram "sliders" at 67 mph I'm only revving 6000 RPM ? Thats 500 rpm below my peak HP @ 6500 rpm. I am going to experiment with putting 4 rollers in at 13 grams (I drilled them to 13 grams) each mixed with 4 of my 12 gram sliders tomorrow just to see if I can get the best of both worlds ? If I don't gain any RPM I'm prepared to drill one more gram out of my 4 rollers that are 13 grams now.

JCL MP250A Lihai 257cc powered / This is how it all ended up here. This info is not for a 50cc-150cc scooter. They are a different animal in some ways to the Yamaha 250 / Linhia powered scoots. I have come to the conclusion that my 257cc Linhia will not go any faster on the top end without a meaningful power upgrade. Like a "real" 295 cc (300) cylinder / piston change plus maybe a little upjetting ? It just dosn't have the torque in its present form to go any faster than 68 mph with my 270 lbs , head right up in the wind resistance situation. I don't care what I do to my variator it just can not change this fact. But I have learned a lot about what works and what is a waste of time. #1 Forget about a bigger or a performance carburator if you don't improve your flow in some meaningful way ie: porting your head and exchange some torque for HP , And get an open / noisy exhaust and and lets not forget a performance pod style airfilter, also more noise. Yes , your intake makes noticable noise with no airbox. " It will sound faster " with just a pod airfilter and a more free flowing exhaust, But in reallity the numberes will change no more than slieghtly if at all. But if you are young and like to be noticed this may have some value. #2 Variator changes gave" ME " (big and heavy) no more top speed. But if a rider is much lighter than 270 lbs. this is what you want to do. #1 On the variator improvment, Shorten your variator boss by 1 1/2 mm do not exeed 2 1/2 mm shorter than stock or your belt will almost climb off your variator at top speed. This will allow your variator to reach its full out high gear. In stock form they stop short of this. #2 on the variator improvement, Exchange your 14 gram rollers for 11 gram "sliders" This will give you everything this motor can offer (with the boss mod too) IMO. I have four 12 gram sliders and four 11 gram sliders. This is what I personally want because I am going to get more power in this engine in the near future. But number 2 will keep you in the higher RPM for maximum excelleration and number 1 will give you full top end capibillities.