Ignition, Gearing, Suspension & Exhaust

IGNITION, GEARING,
SUSPENSION & EXHAUST

 

For ignition I went with the battery-less Motoplat from TODD HENNING, Provincetown, Pennsylvania. This ignition gives you a hot spark from first kick to maximum revs, without a battery as it is not a total-loss system. The rotor is smaller and allows you to rev the motor quicker.
This system comes complete with coils and is milled to the stator cover you send, which is then returned to you completely timed. You also receive complete installation and wiring instructions.
While this is the hot setup, points with the total-loss system do work fine, as long as your battery is in a perfect state of charge and the points are set absolutely perfect.

In a conversation with Knobby Clark I asked him about the point system; he told me that was all they had back then. You could rev the Honda 250 6-cylinder to 12,000 rpm.
You may need to double-spring the points to keep them from floating at high RPM, and it is a good idea to check the points after every race. You can also remove the alternator rotor once it is timed to reduce weight on the crank and get a quicker revving motor. Bosch coils with built-in ballast resistors are a good choice for a hotter spark.

The carburetors used were 34mm Mikuni round-slides. I used 34mm for more fuel due to the increased flow from the porting done to the head. Carburetor setup was: 3.0 slides, 6DP17 needles on the 3rd notch, 159-Q5 needle jet, 40 pilot jet, 210 main jet, air jet screw 2-1/2 turns out. The throttle cable came from the 1976 Honda GT500 to match the throttle assembly.

I used gearing from SPROCKET SPECIALISTS, Palermo, Cailfornia, in the following sizes: front: 15-, 16-, 17-, 18-; rear: 30-, 33-, 35-. I chose a 520 chain for its lighter weight and narrowness, which lets you fit a wider rear tire. This gearing allows me to gear for any track! For example: for Roebling Road, Georgia, I use a 17-33, and for Daytona I use an 18-30, because of the long straights and high speeds turned there. At Daytona with shorter gearing the bike would reach peak RPM too quickly and not be able to stay up with the other bikes.

The exhaust system is comprised of header pipes for a Honda CB450 2-into-1 exhaust, cut and welded to a set of tailpipes from JEMCO PIPES, Houston, Texas. These tailpipes come completely welded and all you have to do is fit the headers and weld on larger brackets. It is wise to rubber-mount the rear hanger brackets as you may crack the pipes from excessive vibration, and get the buzziest feet you've ever had.

For the front suspension I stayed with the stock 1972 Suzuki GT750 components. I use a 1/2 in preload spacer and 10 weight oil to Suzuki specifications. In the rear I use a set of Koni shocks with dampening adjustment set at 2, and have found this to be perfect for most tracks except for Road Atlanta, which has a sharp transition comming out of the "esses" and further up the track going into "gravity cavity".
However, this is an area that is different to each rider.