|FOX MANUFACTURING COMPANY
5305 TOWSON AVE. - FORT SMITH ARK. 72901
PHONE (501) 646-1656
120 TWIN CYLINDER
Since this is one of the very first twins we have produced, we would like very much to hear what success and problems you may experience. A parts sheet will be available at a later date.
The Fox 2 cylinder 20cc motor was designed to power large radio controlled model airplanes. We leave it up to the judgment of the purchaser as to its suitability to the particular purpose he has in mind.
The Fox Twin is designed to operate on prepared model airplane fuel having castor oil based lubricant. For best performance we recommend either Duke's Fuel or Missile Mist fuel. The Fox Twin also runs quite well on an economy mixture of fuel composed of four parts methanol and one part castor oil.
In selecting your propeller remember that the Fox Twin is a high speed machine designed to run in the 11,000 to 14,000 RPM range.You would use an 8" propeller on a 15, a 9" propeller on a 29, an 11" propeller on a 60, so doubling the displacement again would suggest a 13" propeller, which is about right for most models. In practice, an 11-8 is about as small as practical and a 16-4 is about as large as practical. Leave the huge propellers for motors that are incapable of revving up.
The carburetor adjustments take some time and must be done systematically to get any sort of satisfactory results. To get the user the best possible start, we have adjusted these carburetors at the time of the factory run-in. If the needles have not been tampered with, you should be able to remove the engine from its box, mount the engine, connect the fuel line, install a propeller, and start it and run it without any further adjustment. We do not recommend that you attempt to fine tune the adjustments until the motor has run for approximately 30 minutes. At this time, if you so desire, proceed as follows:
Start the motor and set the throttle about 1/3 of the way open. Leave both glow plug heaters on. Then, very slowly, a few degrees at a time, screw the low speed mixture needle in to obtain the highest RPM. Then back out a quarter turn. Then follow the same procedure on the other carburetor. Next, open the throttle wide open and proceed to adjust one high speed needle until you find the point of maximum RPM, then back the needle out very slowly until you detect a slightly perceptible power loss. Then repeat this operation on the other carburetor. Since there is some interrelation of the carburetor, this whole procedure should be repeated if major adjustments were made. Once this has been done, it should not have to be repeated more than twice a year. Once as cold weather comes on, and once as hot weather comes on.
The Fox Twin burns about two ounces of fuel a minute. This is quite a bit of fuel and a pretty decent fuel flow is required. We recommend you use no fuel line smaller than .100 ID, which is the inside diameter of the large Fox fuel lines. Popular polyethylene tanks on the market today are normally equipped with a piece of tubing to go inside for pick up. This is too small in diameter and should be replaced with a piece of large Fox surgical tubing. The surgical tubing will deteriorate slowly in fuel, and should be replaced every two or three months. We also recommend the 1/8" tubing in the top of standard fuel bottles be replaced with 5.32" OD fuel tubing.
BREAK IN PROCEDURE
There is no need to baby this engine or have a prolonged break in. If you have an airplane to fly, then fly it, but bear in mind that until the rings seat, there is sufficient friction in the engine so that if it misfires on low speed, it will probably quit. For this reason, we do recommend you not get your bird out of landing range. As the rings become seated this tendency disappears.
The Fox Twin is designed to be firewall mounted on a good, rigid, well supported firewall.
The Fox Twin can be disassembled with no problem, except that the front connecting rod and crank center section can only be removed at the factory. When reassembling, be careful that the ring is over the positioning pin, and push the cylinder straight on to avoid the ring catching in the ports.
|PARTS FOR FOX TWIN|
|Wrist Pin Keepers/td>||26040||.75|
|Crankshaft Front Section||- - - - - - - - - -||54.00|
|Crankshaft Center Section|
|Crankshaft Rear Section||22.00|
|Thrust Washer Wedgelock||TW005||3.00|
|Head Screws (Pkg of 8)||1.50|
|Cylinder Screws (Pkg of 4)||1.00|
|Case Screws||1.00 ea|
|Ball Bearing - Front||13742||10.00|
|Ball Bearing - Center||16.00|
|Ball Bearing - Rear||26042||10.00|
|Idle Stop Screw & Spring||26062||.75|
|Low Speed Mixture Control||26063||1.25|
|High Speed Mixture Control||26064||1.25|
|Idle Stop Arm||26065||2.50|
|1/4-32 Nut (Pair)||26070||.75|
|Throttle Connecting Arm||4.00|