Setting BT Evo Timing


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By Chris Troudt

What I'm describing here is just for setting the factory spec timing for a BT Evo that's not heavily breathed on. Factory advance curves are not always ideal for high performance Evos. I won't elaborate on aftermarket programmable ignition modules here.

Get yourself one of those clear plugs that screws into the timing hole. The best I've found are from the dealer. They have excellent clarity, they're long enough to contact the flywheel and scrape off the oil, and the threads are decent. Some of the CCI or DragSpec ones are pure junk. It helps to have fairly clean oil -- if it's been a while since the last change, it can make it hard to see the timing mark. It also helps to have the bike parked in the shade to reduce the sunlight washing out the timing light flashes.

The BT Evo flywheel usually has three marks. These vary depending on the model year. They all have a radial straight line. This indicates TDC for the front jug. This is the easiest mark to see and makes it a real breeze to set the timing with a dial-back light. Of course, not everyone has one of those. In addition, there's a single dot mark and a double dot mark. The single dot indicates 35 degrees BTDC for the front jug, and is the max advance mark for US bikes. The double dot on the early models indicates TDC for the rear jug. On later models it indicates 20 degree BTDC for the front jug and is the max advance mark for the exported bikes. (Less advance due to poor quality fuel I assume.)

So, to get set up, you need the bike warmed up, the clear plug installed in the timing hole (hole in left case just below and between the base of the cylinders), the timing light power connected to the battery, and the timing light pickup attached to the front plug wire. The timing cover should also be removed. Adjusting the timing is done by moving the sensor/breaker plate inside the nose cone. The rotor is driven by the camshaft and turns counterclockwise when facing the nose cone. Thus, turning the plate clockwise will advance the timing and turning it counterclockwise will retard the timing.

The two studs securing the plate should be loosened enough to allow it to be moved, but not so loose that the plate can move easily with vibration. It's easier to check/adjust the timing with two people, but it can be done by you using the throttle lock. Max advance occurs at 2500RPM, so start the bike and bring it up to at least that point. Aim the timing light at the clear plug and look for the single dot. It should be centered in the window. The width of the timing hole is roughly 5 degrees of crank rotation. If the dot is rear of center, the timing is too advanced and the plate should be turned slightly counterclockwise. If the dot is forward of center, the timing is too retarded and the plate should be turned slightly clockwise. Doing this alone will require the bike be shut down, adjusted, and retested. With two people, one person can manage the throttle and adjust the sensor/breaker plate while the other person checks things with the light. Good communication here is a plus.

With a dial-back light, the control is set to 35 degrees (or whatever max advance your motor requires), and instead of the dot, the TDC line on the flywheel should be positioned in the center of the timing hole. If the motor requires some max advance other than the marks provided on the flywheel, then a dial-back light becomes an absolute necessity. (I don't know how I ever lived without a dial-back timing light.) If you're absolutely unable to find the timing mark in the window, even after playing around with the sensor/breaker plate, you may have to get your bearings by static timing it first.

Raise the rear wheel off the ground. Pull the plugs out and ground the plug wires. Pull out the clear timing plug for better visibility. Shift the tranny into 4th or 5th, and slowly rotate the engine by turning the back wheel in the forward direction. With your thumb over the front spark plug hole you'll feel pressure when the front piston starts on its compression stroke. Continue rotating the engine until the TDC mark (line) in positioned in the center of the timing hole. Turn on the ignition, activate the timing light trigger, and aim it anywhere that will allow you to observe it flash. No need to aim it at the timing hole -- you already know the exact position of the flywheel. The object here is to move the sensor/breaker plate until you get a flash from the timing light. At that point, you know you have the timing set for 0 degrees advance at 0 RPM. This establishes the baseline timing.

Once the engine is started it will have some amount of advance that increase with RPM, up to the max advance at some particular RPM. (35 degrees at 2500 RPM is typical.) The relationship between the timing advance and the RPM is determined either by the timing curve programmed in the ignition module or by the behavior of the weights and springs in a breaker point system. One of the nice features of most aftermarket ignition modules is their status indicator light. This light takes the place of a timing light while performing the static timing procedure I just described. It's important to note here that static timing only establishes rough baseline timing and tells nothing at all about the max advance. It is useful for getting a new or rebuilt engine close enough to start, or for finding that evasive timing mark, but it should never be a substitute for final max advance adjustment using a timing light. A happy motor is a properly timed motor.

 

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