Generac Power Systems GTH - 990, Owner'S Manual

7

Figure 8 — Air Cleaner

Option 2

1.  Remove air cleaner cover.
2.  Empty dust out of cover. 
3.  Gently pull filter out of air cleaner housing.
4.  Clean inside of housing with damp cloth.
5.  Push new air filter into housing.
6.  Reinstall the air cleaner cover.

Figure 9 — Canister Style Air Cleaner Components

REPLACING THE SPARK PLUG

Replace the plugs every 100 hours of operation or once each year, 

whichever comes first. This will help the engine to start easier and 

run better.
1.  Stop the engine and pull the spark plug wire off of the spark 

plug. 

2.  Clean around the spark plug and remove it from the cylinder 

head.

3.  Set the spark plug gap (Figure 10) to 1.1 mm (0.043 in.). 

Install a correctly gapped spark plug into the cylinder head.

Figure 10 — Spark Plug Gap

CLEANING SPARK ARRESTOR SCREEN

If the engine exhaust muffler has a spark arrestor screen, inspect 

and clean the screen 

every 100 hours

 of operation or once each 

year, whichever comes first.

NOTE:

If using the engine on any forest-covered, brush-covered or 

grass-covered unimproved land, it must have a spark arrestor. 

The spark arrestor must be maintained in good condition by the 

owner/operator.

Clean and inspect the spark arrestor screen as follows:
Inspect the screen and replace if it is torn, perforated or otherwise 

damaged. 

DO NOT USE

 a defective screen. If the screen is not 

damaged, clean it with a commercial solvent.
If the spark arrestor is found to be damaged or defective, replace it.

SERVICE AND ADJUSTMENTS

ENGINE SPEED



 The engine speed was properly adjusted 

at the factory and should require no addi-

tional adjustment. Do not attempt to change 

engine speed. If the engine is running too 

fast or too slow, take the engine/equipment 

to an authorized service center for repair 

and adjustment. CHANGING THE ENGINE 

GOVERNED SPEED WILL VOID THE ENGINE 

WARRANTY.

The operating speed of this engine is maintained by a mechanically 

controlled governor. 

DO NOT

 try to adjust the governed speed set-

ting for the following reasons:
•  Operating the engine at high engine speeds is dangerous and 

increases the risk of personal injury or damage to the equip-

ment.

• Operating the engine at low engine speeds with heavy loads 

may shorten the engine’s life.

COVER

AIR FILTER

ELEMENT,

PRIMARY

HOUSING

AIR FILTER

ELEMENT,

SAFETY

Maintenance