Test 39 - Check Carburetion; Test 40 - Valve Adjustment - Generac Power Systems 4451 & 4986 Repair Manual

section 6
Diagnostic tests
PROCEDURE:
1. Remove the fuel line from the fuel filter on the inlet side of the
carburetor. Use a suitable catch can to catch fuel.
2. Crank the engine over, fuel should flow from the fuel line. If fuel
does not flow, verify that fuel is available to the pump. If fuel is
available to the pump inspect the fuel filter, pulse line, and or
replace the fuel pump.
RESULTS:
Refer to flow chart.

TEST 39 - CHECk CARbURETION

PROCEDURE:
Before making a carburetion check, be sure the fuel sup-
ply tank has an ample supply of fresh, clean gasoline.
Check that all shutoff valves are open and fuel flows
freely through the fuel line.
Make sure the choke operates properly.
If the engine will not start, remove and inspect the spark
plug. If the spark plug is wet, look for the following:
• Overchoking.
• Excessively rich fuel mixture.
• Water in fuel.
• Intake valve stuck open.
• Needle/float stuck open.
If the spark plug is dry look for the following:
• Leaking carburetor mounting gaskets.
• Intake valve stuck closed.
• Inoperative fuel pump.
• Plugged fuel filter(s).
• Varnished carburetor
If the engine starts hard or will not start, look for the
following:
• Physical damage to the AC generator. Check the
Rotor for contact with the Stator.
• Starting under load. Make sure all loads are discon-
nected or turned off before attempting to crank and
start the engine.
• Check that the choke is working properly.
1. Remove fuel line at carburetor and ensure that there is an
adequate amount of fuel entering the carburetor.
2. Remove the float bowl and check to see if there is any foreign
matter in bottom of carburetor bowl.
3. The float is plastic and can be removed for access to the
needle so it can be cleaned.
4. With all of this removed carburetor cleaner can be used to
clean the rest of the carburetor before reassembly.
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5. After cleaning carburetor with an approved carburetor cleaner,
blow dry with compressed air and reassemble.
Shelf life on gasoline is 30 days. Proper procedures
need to be taken for carburetors so that the fuel doesn't
varnish over time. A fuel stabilizer must be used at all
times in order to ensure that the fuel is fresh at all times.
RESULTS:
If carburetor is varnished, clean or replace. Refer to
Flow Chart.

TEST 40 - VALVE AdJUSTMENT

ADJUSTING VALVE CLEARANCE:
The valve lash must be adjusted correctly in order to pro-
vide the proper air/fuel mixture to the combustion chamber.
Adjust valve clearance with the engine at room tem-
perature. The piston should be at top dead center
(TDC) of its compression stroke (both valves closed).
An alternative method is to turn the engine over and
position the intake valve fully open (intake valve spring
compressed) and adjust the exhaust valve clearance.
Turn the engine over and position the exhaust valve
fully open (exhaust valve spring compressed) and
adjust the intake valve clearance.
Correct valve clearance is given below.
intake valve 0.002-0.004 inch (0.05-0.1 mm)
exhaust valve 0.002-0.004 inch (0.05-0.1 mm)
FEELER GAUGE
ALLEN WRENCH
Figure 6-51. – Adjusting Valve Clearance
1. L oosen the rocker arm jam nut. Use a 10mm allen wrench to
turn the pivot ball stud while checking the clearance between
the rocker arm and valve stem with a feeler gauge (see Figure
6-51).
2. When clearance is correct, hold the pivot ball stud with the
allen wrench and tighten the rocker arm jam nut to the specified
torque with a crow's foot. After tightening the jam nut, recheck
valve clearance to make sure it did not change.