It all started one evening while shutting down my garage, after a tidious work of setting up of drag machine in my friendís garage, for a Bangalore speed run. A passer-by halted near the garage entrance looked like he needed a help since his machine was hustling as and when he was trying to rave it up
The person got down expecting some assistance, a quick glare into the race machines parked in the garage turned him inquisitive, after all a professional garage.
The conversation started among the person who introduced himself as Vincent Pradeep and the old mechanic Aleem.
On further confabulation revealed he had stopped his bike was shattering Aleem was quick to respond to go to a garage stationed half kilometre further. Vincent wondered as he was abashed since even he knew it was minute trouble (we fix up only rare bike dirt and rag engines). After further solitation I started up the bike sort the main culprit the plug which was over flooded due to wrong tuning. The Serge appears so called tuners rich tuned the carburettor. The man then went away and appeared next morning.
He claimed that one of the local mechanic Mr. Dutta who showcased himself as tuner and who had perform few modification with a promise to change the dynamism of the engine had screwed it, since the engine never responded until raved hard and the drivability in the city condition was distressing. I explained to him that ours was a professional race garage that perform proficient tuning work for auto cross, motocross and drag setups and also was not a commercial establishment for regular services and rebuilding of machines.
The requestee approach of Vincent made me access his machine condition and further substation by Vincent made me understand that his engine was medalled by a wannabe tuner who knew no basics of two stroke mechanism and had ported the exhaust according to his whims and fancy which had swindled the performance .
I donít promise him for a rocket performance since the bore was ported unscientifically which had rapidly increased the bandwidth thus killing the drivability and practicality of the engine. The chamber look done up by NASA scientists (all thanks to Mr Dutta).
The greatest challenge for 2 stroke tuner to setup equivalence a lot end and high end rpm since one can eat up another, perhaps Vincent request was a cheerful street machine which would enable commanding and would demand head turn on the lookers . my suggestion to the newbie was to pluck a 115cc bore, RX in Pakistan another south east Asian country or a Rx king bore, which establish themselves in the worked of performance of my customer beating college stunters, ladakh tourers and last but not the least my autocross machines. But Vincent was in a dilemma weather to opt for a RX king barrel and puzzle himself for few moments by insisting me on setting up his engines by re-structure the existing port setup which was not my notion as I always laid my hands on virgin barrel which assured everlasting performance and a fond trust and affirmed my tuning.
Eventually made up my mind to set the machine which have accomplish herculin task by proving themselves in performing 10 lap autocross racers and the piston and rings remaining fresh. But the above mention bore was high speed bore 4 TL 10 which has a greater bandwidth in comparison to 4TL00 but 4TL00 has a better low end torque which is better understood by experts or by specialists who draw maximum benefits from 4TL00 as stated above 4TL10 by default as a larger bandwidth proportionately higher BHP (would explain in greater details with theoretical values in my next post) . in the present setup, the abrupt increase in dimension and messed up angles where the culprit in destruction of complete low to mid-range drivability.
As an unsatisfactory move I inlaid a cognitive diagnosis of setup and decided on few factors for preferably superior performance as the head of the 4TL10 bore which was used for the finer option for the stock barrel but since porting of the cylinder in exhaust and transfer ports results in drastic reduction of compression which proportionately kill the lower to mid-range performance where the top curb is slept and the bandwidth improved will not do no good as the drivability is disolated therefore I had two option of facing the squish to increase compression thereby compensation the compression loss or two use a RX King head which is by default a high compression head due to its shorten squish design the later was selected as suggested by me after the head work the NASA made chamber by Mr. Dutta was chucked away naturally. The next task was to fabricate the chamber to corroborate with abrupt port dimension and tactless port angles. Dial gage was employed and the inaccurate dimensions which were close by noted down and same was fed to stimulator to get the accurate expansion chamber dimension and same was fabricated as per stimulator dimension with the local fabricator who regulates our chamber regularly. The expansion chamber phenomena is another major, vital in two stroke topic which is a game changer for any two stroke engine and it largely it influence by theory of waves which should be discussed in any of the further thread.
The next damage control was done through ignition setup. When the spark happens in relation to crank degree before the TDC of the piston something needs to beard it according to engine RPM so that maximum combustion pressure of fuel and air mixture happens between 15 to 20 degrees of TDC that is necessary for most of the power to be transmitted to the gears. As engine bandwidth increases the amount of time being at a set amount before TDC to being at top centre decreases, going only by this aspects it will be ideal for CDI to increase the BTDC of the RPM increases in a linear fashion thereby RX king cdi magneto was flanged which is idea for the purpose.
The above three quints essential were met after a period of 5 days. The carburettor was untouched at this stage as vitamin M did not support. Initially the favourable bandwidth was at higher RPM but the favourable bandwidth now shifted to mid-range as the torque curb was in comfort zone of drivability.
The greatest challenge in 2 stroke tuning has been striking balance higher and lower RPM which is otherwise easy in 4 stroke engine and quite often unscientific porting leads to destruction of performance which is contrary to its purpose. In a 2 stroke engine porting alone will lead to more cons and if other parameters are composted with respect to the level of porting a nearby design performance may be achieved by facilitating the port work by some of the parameter mentioned above.
The machine now a joyful street ride with desired performance with still lot of options left.
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