KDX 250 Ignition Timing

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tlevta
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KDX 250 Ignition Timing

Post by tlevta »

I've recently rebuilt my motor, and I'd like to double check my timing with a dial indicator. How many millimeters below TDC should it be? I can't find anything in the factory service manual listing this. Yeah, I know about the marks on the stator plate.
pumpguy
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KDX 250 Ignition Timing

Post by pumpguy »

I can't answer your question, but unless your bike has breaker points to time the ignition spark, you'll have to use a degree wheel to set the timing, and a timing light with the engine running to see where the timing actually is.

To set this up, first, set the piston at TDC, and put matching marks on the flywheel and on the ignition housing. This is mark A. Next, with these matching marks lined up, mount a degree wheel on the engine shaft, along with a stationary pointer pointing at 0 on the degree wheel. Next rotate the engine shaft backwards the number of degrees you want the ignition to be advanced, and put another mark on the ignition housing that lines up with the mark on the flywheel. This is mark B. Now, remove the degree wheel and start the engine. Use the timing light to see how close the flywheel mark is to mark B. Now adjust the stator plate clockwise or counter-clockwise as needed and check again.

You may find better or worse performance depending on where the actual ignition timing is.

Good luck.
tlevta
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Re: KDX 250 Ignition Timing

Post by tlevta »

I'd try your method, but the nut holding the flywheel on the crank is recessed. So I'm not sure about mounting the timing wheel.
pumpguy
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KDX 250 Ignition Timing

Post by pumpguy »

Just about any method would work. You just want the degree wheel to run concentric with the shaft center. Maybe double sided tape, a cork or rubber stopper stuffed in the flywheel nut.... I'm sure you'll think of something.
pumpguy
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KDX 250 Ignition Timing

Post by pumpguy »

OK, another way to do this is by direct measurement and geometric construction. The stock ignition timing for the KDX 200 H Series. is 21 degrees before TDC. Your KDX 250 is probably different; I don't know.

So, measure the OD of your flywheel. Then take a pair of compasses and draw a circle that is the flywheel's diameter. Now take a degree wheel (360 degree protractor) and make 2 marks on the circumference of that circle that are 21 (or whatever) degrees apart. Now measure that distance along the circumference (not straight line point-to-point) of the circle you've just drawn. This is your distance between marks A and B on the flywheel.

Ideally, you would want the degree wheel to be the same diameter as the flywheel, but best accuracy would come from a larger degree wheel, the accuracy of your circle diameter, the accuracy of your degree spacing, measurement, and marking.

Let us know how this works for you.
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rbates9
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KDX 250 Ignition Timing

Post by rbates9 »

Why?????? Does it run? Good? If yes to both then ride it...
tlevta
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Re: KDX 250 Ignition Timing

Post by tlevta »

The bike was running rich after I went down 2 sizes on the main jet. It had a slight hesitation between 1/8 and 1/4 throttle. Good midrange power, but top end was kinda weak. Since I'm using an aftermarket crank assembly, I was thinking I needed to verify the ignition timing with a much more accurate method.

So this afternoon I pulled the flywheel and just retarded the timing by using the marks on the stator plate. Bike starts and runs much better now.
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Re: KDX 250 Ignition Timing

Post by KDXohio »

There's a difference between running good and running at it's best if he wants to tinker let him tinke!
1990 KDX200 FMF Fatty, Answer VFC silencer, VForce 3 Cage, Wiseco Piston, KX125-J series KYB USD fork conversion, Race tech goldvalves, J series front brake assembly, air-box snorkel removed, Acerbis Headlight, KX450F Front fender, Pro Taper RM bend bars, ASV front Brake lever, MSR Clutch perch and lever, RB Head mod, 36mm PWK carb, Trail Tech Kickstand.
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