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http://www.ultralightnews.ca/hirth-engines.htm Page 23 of 31
The Ultralight News
Pull plastic strainer from around the mixing tube and, if necessary, clean with fuel. Screw out the main jet
from the mixing tube and check for damage or grime. Replace immediately if damaged; clean with gasoline if
dirty, then blow out with compressed air. Never push a sharp object through the main jet as that will destroy
it.
Reassemble in logical reverse order. When putting the float chamber back on, insure that the bolts are
properly seated. Torn and/or frayed gaskets must be exchanged immediately for original replacement gaskets.
9.5Inspecting the air filters
To remove the air filters, loosen the clamp on the air filter with a screwdriver, and slide the air filter off from
the carburettor flange.
Wash out the air filter with fuel and then dry. To do this, blow out the filter with compressed air from inside
to out. Check the filter for damage and replace any defective filters and clamps.
To install the air filter, insert over the carburettor flange and fasten the clamp with a screwdriver again.
9.6Inspecting the fuel lines
Check the fuel lines between fuel ? diaphragm pump, carburettors and fuel tank for leakages and/or other
damage. Replace leaking and/or damaged fuel lines.
9.7Inspecting pulsation lines
Check the pulsation line between the vacuum nipple on the crankcase and the pulse connection of the fuel ?
diaphragm pump for leakage and/or other damage. Replace the leaking and/or damaged pulsation line.
It is recommended that the spark plugs be checked one after the other to avoid mixing up the sparkplug leads
and their connecting positions.
9.8Inspecting the condition of the sparkplug leads
Remove the sparkplug leads and check the contact socket inside for corrosion. Check the SAE-contact (the
screwed on contact hood) of the sparkplug for corrosion or "deposits". If there is corrosion or "deposits",
replace the sparkplug lead and SAE- contact of the sparkplug (usually here the sparkplug would be
completely exchanged - see next paragraph).
9.9Installing and removing sparkplugs
To uninstall the sparkplug, remove the sparkplug lead. Loosen the sparkplug with the sparkplug wrench and
unscrew it.
Before installing the new or still serviceable sparkplug, the air gap (0.8 mm) is to be checked with a feeler
gauge and adjusted as required.
Screw the sparkplug into the cylinder head with a sparkplug wrench and torque to the correct setting.
9.10Condition of the sparkplug
The spark plug should have a dry bright brown colour tone on the central electrode, the insulator of the
central electrode and the earth side of the case. If the colour tone changes to a bright very dry grey, the
engine is running very hot and the mixture is too lean. Where there is a wet dark brown to black colouring,
the engine is running with too thick a mixture. In both cases, AATI Pty Ltd or your Hirth distributor should
be contacted.
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