Engine Tuning
by  Joe Bucker

 

I use two methods to time my race engine; a degree wheel and positive stop device in the spark plug hole, or a special dial indicator, which fits in the spark plug hole. The degree wheel bolts on the ignition side by means of a 13mm socket bolted to the degree wheel.

The degree wheel attaches to the ignition rotor by the socket sliding over the rotor bolt and being secured by the setscrews. You attach a tie-wrap for a pointer from the cylinder (the little round things that keep the cylinder fins from "ringing" and are staggered about), and put a positive stop device into the plughole to stop the piston near TDC.

With all the plugs removed, the engine will turn over easily by the degree wheel. The nuts on the degree wheel bolt and socket assembly should be tight so the wheel does not slip while turning the crank. So turn the engine "forward" until the left piston hits the positive stop, and record the number. It doesn't matter where on the wheel the pointer points to when the piston hits it. You then turn the crank "backwards" until the piston stops again, and record that number.

If you hit 95° going forward (counterclockwise) or normal engine rotation, and 65° going backward, then 80° is TDC. Take your positive stop device out and put engine at 80°. 23° BTDC is the standard timing number so rotate crank backwards from 80° minus 23° to 57° and remove wheel by the setscrews as not to move crank. Point the timing marker to the line on the rotor and you have your mark for that cylinder. Repeat for center and right because your crank may not be in "phase". Set up your inductive timing light and set the timing for reach cylinder at full throttle or 8000 rpm which is the rpm limit of most timing lights.

You can do the same thing with the dial indicator in the spark plug hole to set your timing. My dial indicator cost $49 and my degree wheel setup about $30. As far as I can tell, the results are the same; one being as accurate as the other.

When you use the timing light, the mark moves around a bit through the rpm range, so set it at full throttle (rpm). A lot of people complain about the mark "dancing" all over the place and not holding a steady mark. You definitely want a steady mark for racing. I have found most of my prob­lems in the ignition rectifier box. This box rectifies the magnetic out­put (AC) to DC through diodes. The diodes let current flow in one direc­tion only and not the other direction. The Kawasaki service manual gives a test procedure for this box, and if followed, will tell you if your ignition rectifier box is good or bad. "Dancing" timing markers result from this box supplying the ignition GDI boxes with DC not fully recti­fied from AC, so instead of a steady voltage supply to the GDI's, the voltage fluctuates and therefore causes the spark signal to fluctuate.

Dancing spark signals can also come from bad pickup boxes or GDI boxes; again the service manual has tests for these also.

Once your engine has accurate timing to each cylinder, and your engine (ignition) doesn't fluctuate, you should produce more horsepower. Dave Schultz said he would never race with an ignition that fluctuates, so taking his advice, I think we shouldn't either.

I also wanted to warn all our members who race that if you use the "Custom FRP" tanks, do not use their gas caps with the vent "switched" on and off through the knob on top. I suffered rod failure this year because the vent switch went bad, the rubber gasket under the knob got soft and clogged the vent hole. This caused me to lose fuel flow to my two outside cylinders more than three times during time runs down the track. The fuel would stop flowing while I was going through the timing lights at 105 mph (1/8 mile). I finally found the cap was bad when on the return lane, seeing my Lectrons dry, I opened the cap to check my gas and heard the "hiss" of air rushing in the tank. Not only did a rod big end come apart, it also sent a needle bearing through the upper case past my leg, and the piston snagged a needle in the transfer port cracking the Stage II cylinder in half.

The cylinder (Stage II) will cost $300 to replace. I had the crank re­built last winter. New rods and all at a cost of $400, so it will be another $400 for a new crank next season, and I had to buy new (used) cases. Very expensive just for a gas cap failure. So members, beware, use unvented gas caps and drain your gas after each race to keep it fresh.

My race bike weighs 349 lbs (no gas), and after I broke my Stage II motor, I home ported a set of spare cylinders. Using the 80° ATDC exhaust port specs (App. 5/16 of an inch), I raised the top of the port, but I did not widen the port, as this is what eats your rings up the worst. I polished and ported the intake and exhaust and matched the intake and exhaust manifolds to their ports. I had to use my stock carbs, as my 38 Lectron PI's won't fit. I run a best of 10.58 @ 119 - 1/4 mile and 6.58 @ 101 -1/8 mile. You guys running 7" slicks, Goodyear has a D-3 compound - very sticky, and this tire sticks. It is probably one reason I got such good times with a mild motor.