Building the SCHROEDER .09

Tank and Needle Valve

 

These instructions were originally written by Roger Schroeder


The tank-mount is cut from a piece of 1-3/4 diameter or larger bar stock aluminium. Refer to the accompanying drawing and turn the outside diameters first, leaving the mounting flange at 1-3/4 diameter as shown by the dotted outline on the drawing. Match the threads on the tank-mount with the previously threaded crankcase. When cutting off the tank from the bar stock leave about .010" to .020" extra mounting flange thickness. This will be removed later.

Turn the tank around and hollow out the interior to a minimum wall thickness of .050". If in doubt about the depth of a cut, leave the wall heavier. There is plenty of fuel volume in the tank. Don't forget to machine the 1-3/16" diameter x 1/32" deep (plus the extra flange thickness you left in the cut-off) recess for the tank cover. Smooth surfaces on the recess are necessary.

The easiest way to put the rear cover on the tank is to first turn a piece of bar stock Aluminium to an O.D. that will be a light press fit into the 1/32" deep recess in the tank. Leave the bar stock in the lathe, coat the O.D. with epoxy, press the tank over the bar and let the epoxy cure.

After curing, carefully cut off the bar with a parting tool leaving .010" to .020" excess thickness on the tank cover. Now turn the tank around, chuck it in the lathe and turn the back cover and flange to the proper thickness. Your light finish cuts will help seal and retain the rear cover in the tank.

Make a paper gasket for the tank-to-crankcase joint and assemble the tank to the crankcase tightly. Loosen and tighten the assembly a number of times until the gasket stops being compressed. Finally assemble tightly, mark the square outline of the tank flange, cut the flange to shape and drill the 3/32" mounting holes. Drill a hole in the tip and install the filler cap. Finally drill an appropriate hole for the fuel line. Now is the time to decide if the needle valve is to be operated from the left or the right side.

All the commercial replacement needle valves I have seen are too large for our .09 engine. For this reason, a drawing for making a needle valve assembly and for a revised venturi is included with this article. Note on this drawing that the needle valve has a two part body consisting of a guide and a seat that screw separately into the venturi.

The valve guide and seat are shown as made from 3/16" brass hex stock, although other material and size stock may be substituted. Obtain a 2-56 screw for making the needle valve. Sharpen one end to an 8° angle and make a 1/4" diameter by 1/16" thick knurled knob to screw on the blunt end of the screw. This knob, plus an 11/16" length of brass tubing is soldered to the screw. Another 1/4" diameter by 1/16" thick knurled knob is soldered to the end of the brass tubing to complete the needle valve.

The valve clip is secured to the venturi by the valve guide and provides a positive ratchet for the needle valve.