CDI advance

Thumper · 12-30-2022, 09:58 PM

CDI units rely on a signal from the pickup on the rotor to time the Coil trigger. So we can buy a modified key to advance the timing physically, placing the rotor 1 to 4 degrees or thereabouts in advance of the normal position.

With this physical change, TDC is essentially misread by the standard CDI unit, but at a fixed number of degrees BTDC. The entire standard ignition curve is advanced exactly the same amount.

But ignition curves should be advanced progressively FROM idle, NOT at idle. Peak advance should be at maybe 2500-to 4000rpm, but with minor or no advance at idle. The key doesn't accomplish this.

I bought a Dyna 2000 for my Suzuki Bandit 1200S years ago. It had 5 advance curves to choose from... mild to extreme. Here is an advance curve for the Buell/HD application of a Dyna 2000 CDI advance device. Selecting which curve you want is a simple turn of a dial (mine had a skinny screwdriver slot, A, B, C, D, E as I recall).

Name: AdvanceCurve.jpg
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Name: AdvanceCurve.jpg
Views: 1795
Size: 107.2 KB

The weird thing is that these devices work even though they send a signal BEFORE the trigger passes the pickup (by the rotor), so how do they know how many milliseconds before TDC to trigger the coil?? The answer is, amount of time between trigger events changes with rpm!

OK, so at idle, the position can be averaged, no problem, but as rpm increases, the device must "GUESS" when to trigger the coil. Therefore, when rpm is changing to shorter duration (increasing in rpm), it must anticipate the change based on delta change over the last 2 revolutions (minimum!). And the same goes for on the way down.

Pretty cool device! Well, there are cheap advance modules available for our typical GY/CG engines. I see one for under $27, with free shipping. Press the little red button and it cycles through NINE different advance curves!

AliExpress listing called "Motorcycle Performance Parts Ignition Ignite System Unit Digital Adjustable DC CDI Racing For GY6 CG 50 125CC 250CC Scooter ATV" It will take a month to get here, but I think it is worth a try.

wheelbender6 · 12-31-2022, 11:10 AM

Good find. I have used a CDI with an advanced, but non-adjustable ignition curve on my 125cc and it really makes it more responsive.

12-30-2022, 09:58 PM	#1
Thumper Join Date: Feb 2021 Location: Kansas City Posts: 2,735	CDI advance CDI units rely on a signal from the pickup on the rotor to time the Coil trigger. So we can buy a modified key to advance the timing physically, placing the rotor 1 to 4 degrees or thereabouts in advance of the normal position. With this physical change, TDC is essentially misread by the standard CDI unit, but at a fixed number of degrees BTDC. The entire standard ignition curve is advanced exactly the same amount. But ignition curves should be advanced progressively FROM idle, NOT at idle. Peak advance should be at maybe 2500-to 4000rpm, but with minor or no advance at idle. The key doesn't accomplish this. I bought a Dyna 2000 for my Suzuki Bandit 1200S years ago. It had 5 advance curves to choose from... mild to extreme. Here is an advance curve for the Buell/HD application of a Dyna 2000 CDI advance device. Selecting which curve you want is a simple turn of a dial (mine had a skinny screwdriver slot, A, B, C, D, E as I recall). The weird thing is that these devices work even though they send a signal BEFORE the trigger passes the pickup (by the rotor), so how do they know how many milliseconds before TDC to trigger the coil?? The answer is, amount of time between trigger events changes with rpm! OK, so at idle, the position can be averaged, no problem, but as rpm increases, the device must "GUESS" when to trigger the coil. Therefore, when rpm is changing to shorter duration (increasing in rpm), it must anticipate the change based on delta change over the last 2 revolutions (minimum!). And the same goes for on the way down. Pretty cool device! Well, there are cheap advance modules available for our typical GY/CG engines. I see one for under $27, with free shipping. Press the little red button and it cycles through NINE different advance curves! AliExpress listing called "Motorcycle Performance Parts Ignition Ignite System Unit Digital Adjustable DC CDI Racing For GY6 CG 50 125CC 250CC Scooter ATV" It will take a month to get here, but I think it is worth a try. Last edited by Thumper; 02-17-2023 at 03:41 PM.
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12-31-2022, 11:10 AM	#2
wheelbender6 Join Date: May 2015 Location: Houston area Posts: 1,902	Good find. I have used a CDI with an advanced, but non-adjustable ignition curve on my 125cc and it really makes it more responsive. __________________ "Its not WHAT you ride; its THAT you ride"
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