User Manual

OFNA RACING , 7 VANDERBILT, IRVINE, CA. 92618 • TEL:[phone]
FORCE 28 PULL START
ENGINES
Thank you for purchasing a OFNA engine. We appreciate your choice and know you will enjoy running it. Please
note that theForce information in engine box is subject to change with not notice.
Carburetor Low end and barrel stop screws are pre-set by factory.... Do not change until break-in is done.
NEW ENGINE BREAK-IN
Your OFNA engine is extremely tight when the piston is at the top of the stroke and turning the crankshaft by hand.
This is normal for a new ABC type engine. The piston and sleeve are matched for fit and the top of the sleeve is
tapered for a tight fit. As you run your engine, this tightness should diminish. There is no cause for alarm, because
as the engine warms up, the brass sleeve will expand faster than the aluminum piston and the engine will turn freer.
As with any new engine, there are many high spots and tight fits in the matching process. High spots create hot
spots that must be broke-in. Therefore, the break-in process is very important to provide good service by the OFNA
engine. So, you must run the engine rich (COOL) for the first three tanks of fuel. We recommend using one gallon
of 20% BYRON’S 2000 as break-in fuel. Other break-in type fuels or added oil is NOT
needed. DO NOT OVER REV THE ENGINE WHEN FIRST STARTING, this could break the piston and over heat
sleeve. Let engine run at low RPM for one tank to break-in connecting rod bearing before starting full break-in.
Break-in the engine in the car, by running the engine at a rich setting. Run the car from a slow to fast speed with
short bursts of speed. You need to buildup a little heat in the engine, but not too hot. In a rich setting, the engine
will run cold. In the leaner setting the engine run hot, this is not good yet. Do not heat up the engine too much at
this time. After about one (1) tank, turn the Master Needle Valve, clock wise, 1/8 of a turn leaner or clockwise.
Keeping the fuel tank full, continue the process until you slowly turn the Master Needle Valve, 1/8 of turn each time,
too a leaner point and in which the engine runs at high RPM and power, but still keep max temp. of 250 deg. F. At
this point you must stop, too lean of a setting will heat up engine and damage the piston. A normal operating
temperature is around 220 to 250 Deg. Temperatures of 300 Deg. and above will damage engine and shorten life.
NEEDLE SETTINGS
Master Needle Valve - main control for fuel mixture. Set at 3 to 31/2 turns from closed. Adjust this needle for
maximum RPM and power without being too lean or too hot. Make sure you start at bottom of needle seat!!
Side Carburetor Needle (Low Speed) - This needle is in the center side of the carburetor and provide throttle
response. It is not the idle adjustment. Set FLUSH with ball end. Turning in is Lean and Out is Rich. Do not adjust
this needle until the Master Needle is set for power and top speed. This will only effect throttle response.
Barrel Stop Screws - Used for adjusting Idle. Set for 1/16th inch gap to start new engines. You can open more for
faster idle.
USE LONG GLOW PLUG WITHOUT IDLE BAR,
OFNA/PICCO #51007 OR 51008 IS RECOMMENDED