My old man has built and raced just about every type of 2 stroke and 4 stroke bike/atv/car. With 50 yrs of his experiance of tuneing them I asked him some questions.
Q) why advance timing?
A) By advancing the timing you are igniting the air/fuel mixture a little sooner.
Q) How does this give more power?
A) It takes time for fuel to burn so the spark always fires before the piston reaches TDC. In other words, the spark fires before the piston is finished with the compression stroke. What this does is gets the air/fuel mixture burning and close to maximum combustion pressure at just the right time.
Q) What happens if its not advanced far enough?
A) It fires too late and you lose power.
Q) What happens if its advanced to far?
A) It fires too soon and you get pre-ignition, and possible
sparatic engine rpms.
Q) I run my banshee +5 will it hurt it?
A) Temp,fuel delivery,atmospheric pressure,elevation,compression,stroke,
squash band will be very crucial.If everything is spot on it still may
be very finicky. So modifying timing could cause harm.
Q) You said finicky can you explain that?
A) Remember your altering fuel/air burn time, so adjustments through out the
mixture ranges will be more susceptible to slight changes in,mixture ratio,
type of fuel,heat,elevation,atmospheric pressure,ect.
Q) I have my banshee jetted perfect. I have done plug chop after plug chop
at every rpm range and the plugs look perfect. But I do notice when I am
between 1/16 and 1/8 throttle the engine seems to have a loppy sound,
almost like its miss fireing but when I pull the plugs they look good, any
suggestions to fix that.
A) YUP thats the finicky word i mentioned. If your jetted correct and you
cant get the engine to run smooth all the way through the rpm ranges
drop your timing down 1 degree at a time untill you hit that sweet spot.
I really didnt wanna drop my timing down so I loaded it up and took it to his house. He tor into it changing jets,needles,needle height,. What would get rid of my 1/16 to 1/8 issue would make the throttle responce horrible. So he put everything back to where i had it, and adjusted my timing from +5 to +2
took it out to test it. BAM perfect everywhere.
I now believe that yamaha set the stock timing on the banshee so its less
susceptible to variables. I hope this information helps someone in the future.
And although I might of lost 1/2 to 1 hp I am much happier how smooth it runs throughout the entire rpm range.