Starting
(Continued)
10. Open the choke.
11. Set throttle to idle position. (carb butterfly plate slightly open)
12. Flip the prop again until the motor runs.
13. Let the motor warm up for 15 or 20 seconds before advancing the throttle.
Needle Adjustments
•
The needle farthest from the motor is the “High RPM” needle. The needle closest to motor is the “Low RPM” needle.
Turning the needles clockwise “leans” the fuel mixture. Turning the needles counter-clockwise “richens” the fuel
mixture.
•
Settings will vary with altitude, temperature, humidity, fuel, carb variances, etc. A general starting point is: 1 3/8 open
on the Low needle, 1 7/8 open on the High needle.
•
Adjusting either needle (primarily the Low) can have a slight effect on the other. Example: leaning the Low needle
can "slightly" lean the high range.
•
Adjust the Low RPM needle until you achieve a smooth idle and a reliable transition to high throttle. Generally if the
motor “stutters” or “coughs” in the mid range or when the throttle is advanced, the low end needle is too rich and
possibly even the high end needle. If the motor dies quickly, the low end is probably lean.
•
Adjust the High RPM needle to peak rpm. A tachometer is a great help, but remember that the RPM may drop a little
bit after every start due to residual heat buildup. Don’t lean the mixture any more than necessary. If the rpm steadily
drops at full throttle or fades on long vertical maneuvers, the motor is too lean and is overheating.
Don't set the needles overly rich to protect the engine. Operating the motor overly rich not only reduces power, it
creates other problems such as poor transition, vibration, pre-mature carbon build up, fouled plugs, excessive exhaust
residue, sticking rings, and overall rough running
.
Trouble Shooting
Motor won't start
•
Check battery voltage (should be 5.0+ volts when checked under load) and all ignition connections, wiring, and
switches (both standard and optical). Wires can break from vibration near connectors. Check and/or swap out
regulators, isolators, or optical switches if using one
•
Check tank venting, clunk position, and fuel flow.
•
Fuel doesn’t move in the line when the prop is flipped or carb doesn’t “prime”? Is the choke plate closed completely?
Make sure tank is vented. Make sure there are no air/fuel links on the engine case or carb mount area. Is the carb or
carb mount loose causing an air leak? Again, look for fuel seepage.
•
Is throttle set at idle or slightly higher after motor “pops” and choke is opened?
•
Make sure prop is flipped over with authority. The ignition won’t fire at low speed.
•
If a lot of fuel drips from carb, the motor might be flooded. If so, remove and dry, or replace, the spark plugs. Try
starting again without using the choke, then use the choke if required.
Other issues
•
Fuel drips continually from carb: Make sure there is no debris in the needle seat. Remove needles and blow air into
the holes. 5
•
Broken prop bolts: In order for bolts to shear, some type of side loading (shear) movement is usually required. If the
bolts are tightened correctly, nothing moves and prop bolts will rarely break. It’s a good idea to replace prop bolts
routinely. Check prop bolts before each flight!
•
Excessive vibration: Check that low rpm needle setting is not too rich. Check prop and spinner balance. Make sure
ignition sensor hasn’t moved. Check that motor mount bolts are secure. Make sure firewall and motor box are rigid.
Some poor designs need added re-enforcement to the firewall/motor box area to eliminate flex.
•
Pink or purple colored cylinders: These colors indicate engine temperature has been too high. Check that needle
settings are not too lean, air flow for cooling is sufficient, oil/gas mixture is correct.
IF ANY PROBLEM PERSISTS, PLEASE CONTACT
DESERT AIRCRAFT FIRST!
We designed and manufactured your engine, and have built, serviced, and analyzed thousands more. We
cover your engine’s warranty, not someone at the field or a stranger on the Internet. Please give us the
opportunity to help first!
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