Split Second ARM1 and EGO1 mounted on the "Serpent" Bike

The "Serpent", a custom that has taken over 30 months to build, started as a 1966 Shovelhead basket case.

The Serpent

Serpent looks like a rigid, right? But it's not. The rear fender is mounted to the swingarm of a Chopper Guys softail frame! This makes it look like a rigid, but have the ride of a softail.

Serpent is built from a 93" stroked shovelhead motor with an STD case. The motor is enhanced with a Spyke electronic ignition, S&S E Shorty carb and Dial-A-Jet secondary fuel circuit. The front end consists of 43mm Ceriani forks and GMA brakes - dual front and single rear. Exhaust is a custom two-into-one with a Supertrapp slipon.

Serpent gets her name from diamondback rattler snakeskin flames in the seat, pillion pad and dash panel.

Split Second Air/Fuel Monitor

Because motors can burn up when they run lean it was felt that for a motor of 90" displacement there would be too much doubt as to the mixture that was running at any given time. Dialing in a beast like that benefits from knowing for sure that you are running a mix that won't detonate or melt down yer moving parts. So a search was made for a fuel mixture analyzer that would work with the bike. That search led to Split Second of Santa Ana, CA.

Using an Air/Fuel mixture monitoring system you can dial in a bike with absolute certainty. To help with the dial-in, a Dial-A-Jet secondary circuit was added to the S&S Super E carburetor. Using the Dial-A-Jet with the Split Second system it was possible to dial the bike richer or leaner and observe the results. Jetting is an art, not a precise science, but it was possible to find the ideal point where the bike runs smoothly, avoiding running lean under throttle.

The mounting points for the Split Second ARM1 and EGO1 are shown below.

ARM1

The ARM1 mounts under the right hand control cluster on the handlebar. It is very light and stays in place using the Velcro that comes with the kit.

EGO1

It took some thinking to find the right spot for the EGO1 gas analyzer. Because the header pipes and 2-into-1 were custom built by Mike Scraggs of California Performance Iron it was not a good idea to drill a hole in that assembly. It is such a fine job (the front pipe fits between the motor and frame without needing to be crushed) that re-creating it would not be easy. Instead, the Supertrapp seemed the likely spot. Because of ground-clearance and other clearance problems the sensor was tightly fitted into a precisely drilled hole at the location shown, and TIG welded in place. It is possible to get away with mounting the sensor this far from the motor because the sensor is heated electrically (four wire) and this compensates for cooling of exhaust gases, providing as well a calibration standard.

After using the Air/Fuel mixture sensor to dial in the bike, the sensor serves to warn of undesirable conditions when changing altitude or other atmospheric conditions cause richer or leaner burning. It gives a strong sense of confidence that this beautiful bike will give many years of pleasant riding.

Some other interesting details: Lubrication is HD 20/50 - NOT straight 50 (or 60 or 70). This is done after a great deal of research and reports by shovelhead owners who claim tens of thousands of miles of riding with no problems. Using 20/50 makes the bike easier to cold start. Remember, multigrade oils were not used by the factory until the mid seventies. After the full breakin (1,500 miles) Prolong additive will be used from then on. The shovelhead was invented before unleaded fuel was required. Valve guides are not hardened to compensate for the absence of lead in the gas, so valves take too much abuse and fail early. Think of Prolong as a kind of lead replacement. It literally eliminates wear from bearing surfaces!

Serpent is a retro bike with state-of-the-art improvements. It is hoped that by combining the old with the new in this way it will be possible to have the benefits of the shovelhead design with few of the drawbacks.

Nelson Johnson, Design Engineer