CLYDE
Super Veteran
Can somebody please enlighten me on which is the better way of setting the cdi timing (mechanical or just use a racing cdi) or can we use both at the same time?Im kinda confuse of my friends bike setting, i know his cdi brt powermax has advancing slope at low rpms yet his mechanic still advance the timing mechanically.
Once the timing has been set somewhere around a few mm before the piston reaches top dead center the bike will run. Too far in either direction and it will run very poorly, but get it close to optimal and it will run nicely. Once it runs well, changes in spark timing have the most effect on the temperature of the gasses that exit out the exhaust port of a cylinder. What this means is that if a spark happens somewhere around 2.5mm before top dead center (BTDC), combustion will complete earlier in the cycle and have time to dissipate its heat into the head, piston, and cylinder before the exhaust port opens. This means that the gasses that exit out the exhaust will be cooler. When the spark happens later, lets say somewhere around .5mm BTDC the combustion process completes later, and the exhaust gasses have less time in contact with the head, piston, and cylinder walls. This means the gasses that exit out the exhaust port will be hotter. Why do we care what temperature the exhaust gasses exit? the hotter the gasses, the faster the gasses will travel down the exhaust pipe. The cooler the gasses, the slower they will travel. So why do we care how fast they travel? Slower gasses will move the powerband of a pipe to LOWER rpms. Faster gasses will shift the powerband of a pipe to HIGHER rpms. So as timing changes, so does the powerband of a pipe. We can use this information to our advantage. If we have variable timing we can have a variable powerband of a pipe, right? So why not have the powerband of a pipe be at lower rpms when the engine is actually at lower rpms and then have the powerband of a pipe be at higher rpms when the engine is actually at higher rpms. This is exactly what happens in cdi’s that have a curve. They start out with more advanced timing at lower rpms (to shift the powerband of the pipe to lower rpms), and then retard the timing at higher rpms (to shift the powerband of the pipe to higher rpms). Some cdi’s dont have a curve though, and you have to compromise. If you do not have a curve on your cdi, you set the timing so the powerband of your pipe is where you want it. Set it more advanced to lower the peak power rpm value, and set it more retarded to have the peak power of the pipe at a higher rpm value.
Once the timing has been set somewhere around a few mm before the piston reaches top dead center the bike will run. Too far in either direction and it will run very poorly, but get it close to optimal and it will run nicely. Once it runs well, changes in spark timing have the most effect on the temperature of the gasses that exit out the exhaust port of a cylinder. What this means is that if a spark happens somewhere around 2.5mm before top dead center (BTDC), combustion will complete earlier in the cycle and have time to dissipate its heat into the head, piston, and cylinder before the exhaust port opens. This means that the gasses that exit out the exhaust will be cooler. When the spark happens later, lets say somewhere around .5mm BTDC the combustion process completes later, and the exhaust gasses have less time in contact with the head, piston, and cylinder walls. This means the gasses that exit out the exhaust port will be hotter. Why do we care what temperature the exhaust gasses exit? the hotter the gasses, the faster the gasses will travel down the exhaust pipe. The cooler the gasses, the slower they will travel. So why do we care how fast they travel? Slower gasses will move the powerband of a pipe to LOWER rpms. Faster gasses will shift the powerband of a pipe to HIGHER rpms. So as timing changes, so does the powerband of a pipe. We can use this information to our advantage. If we have variable timing we can have a variable powerband of a pipe, right? So why not have the powerband of a pipe be at lower rpms when the engine is actually at lower rpms and then have the powerband of a pipe be at higher rpms when the engine is actually at higher rpms. This is exactly what happens in cdi’s that have a curve. They start out with more advanced timing at lower rpms (to shift the powerband of the pipe to lower rpms), and then retard the timing at higher rpms (to shift the powerband of the pipe to higher rpms). Some cdi’s dont have a curve though, and you have to compromise. If you do not have a curve on your cdi, you set the timing so the powerband of your pipe is where you want it. Set it more advanced to lower the peak power rpm value, and set it more retarded to have the peak power of the pipe at a higher rpm value.
, is it to help the cdi more in its function? like giving the bike more low end torque or better topend
