DUROMAX XP20HP User manual

This manual provides information regarding the
operation and maintenance of these products. We
have made every effort to ensure the accuracy of the
information in this manual. We reserve the right to
change this product at any time without prior notice.
5800 Ontario Mills Pkwy
Ontario, CA 91764 USA
www.duromaxpower.com
Call our Customer Care Team Toll Free 8-5pm PST Mon-Fri
844-DUROMAX
REV: XP20HP_servicemanual_rev01112023
XP20HP
SERVICE MANUAL

CONTENTS
1. Maintenance Schedule................................................................................................... 4
Break-In Period ............................................................................................................... 5
High Altitude Operation ................................................................................................. 5
Checking the Oil .............................................................................................................. 6
Changing the Oil.............................................................................................................. 7
Changing the Air Filter.................................................................................................... 8
Spark Plug Maintenance .............................................................................................. 10
Emptying the Gas Tank ................................................................................................ 12
Storing the Engine for Same Day Use ........................................................................ 14
Storing the Engine for Use Within 30 Days................................................................ 15
Storing the Engine for Longer Than 30 Days............................................................. 16
Maintenance and Care
3. Specications................................................................................................................. 23
Adjustment and Torque Value Specications ........................................................... 24
Engine Diagrams........................................................................................................... 25
Wiring Diagram ............................................................................................................. 27
Specications
2.
Common Engine Parts.................................................................................................. 18
Common Engine Parts
4.
Troubleshooting............................................................................................................ 28
Troubleshooting
5.
Maintenance Log........................................................................................................... 29
Maintenance Log

4
MAINTENANCE AND CARE
Proper routine maintenance of your engine is essential for safe, economical, and trouble-free
operation. It will also help reduce air pollution.
Maintenance Schedule
Remember that this schedule is based on the assumption that your machine will be used for its
designed purpose. Sustained high-load, high-temperature operation, or use in unusually wet or
dusty conditions, will require more frequent service.
SERVICE
EVERY USE
1ST MO. OR
8 HRS.
(BREAK IN)
EVERY 3 MO. OR
50 HRS. OF
HEAVY USE
EVERY 6 MO.
OR 100 HRS. OF
NORMAL USE
EVERY 12 MO. OR
300 HRS.
EVERY 3 YRS. OR
500 HRS.
ENGINE OIL CHECK CHANGE CHANGE CHANGE
AIR CLEANER CHECK CHECK CHANGE CHANGE
SPARK PLUG CLEAN /
ADJUST
CLEAN /
ADJUST
SPARK
ARRESTOR
CHECK CLEAN
IDLE SPEED CHECK /
ADJUST
VALVE
CLEARANCE
CHECK /
ADJUST
FUEL TUBE CHECK CHECK /
REPLACE
FUEL TANK /
FILTER
CLEAN
COMBUSTION
CHAMBER
CLEAN
4
WARNING: Improper maintenance, or failure to correct a problem before operation, can
cause a malfunction in which you can be seriously injured or killed. Always follow the
inspection, maintenance recommendations, and schedules in this instruction manual.
●Make sure the engine is o before you begin any maintenance or repairs.
●Let the engine and exhaust system cool before touching.
●To reduce the possibility of re or explosion, be careful when working around
gasoline. Use only a nonammable solvent, not gasoline, to clean parts. Keep
cigarettes, sparks, and ames away from all fuel-related parts.

5
Break-In Period
As the best practice for any new combustion motor it’s recommended to perform the break
in procedure as follows:
●Run the engine for the rst 6-8 hours on conventional oil, then change the oil. After
the break-in period synthetic oil may be used.
●During the break in period of the rst 6-8 hours keep the engine speed under 50% for
optimal results.
●Check and clean the air lter if necessary after the break-in period.
High Altitude Operation
At high altitudes, the standard carburetor air/fuel mixture will be too rich. The performance will decrease,
and fuel consumption will increase. A very rich mixture will also foul the spark plug and cause hard starting.
Operation at an altitude that diers from that at which this engine was certied, for extended periods of
time, may increase emissions. High altitude performance can be improved by specic modications to
the carburetor. If you always operate your engine at altitudes above 3,000 feet (900 meters), have a dealer
perform this carburetor modication. This engine, when operated at high altitude with the carburetor
modications for high altitude use, will meet each emission standard throughout its useful life. Even with
carburetor modication, engine horsepower will decrease by about 3.5% for each 1,000-foot (300-meter)
increase in altitude. The eect of altitude on horsepower will be greater than this if no carburetor
modication is made.
When the carburetor has been modied for high altitude operation, the air/fuel mixture will be too lean for
low altitude use. Operation at altitudes below 3,000 feet (900 meters) with a modied carburetor may cause
the engine to overheat and result in serious engine damage.
Note: Jet kits available for purchase upon request, please contact us at 844-DUROMAX to set up your
parts order.

MAINTENANCE AND CARE (CONTINUED)
Checking the Oil
6
Check the oil
The engine is equipped with an automatic shuto to protect
it from damage due to low oil. Nonetheless, you should check
the oil level of the engine before each use to ensure that the
engine crankcase has a sucient amount.
To check the oil level:
a. Make sure the engine is on a level surface.
b. Unscrew the oil ller/dipstick cap.
c. With a dry cloth, wipe the oil o of the stick on the
inside of the cap.
d. Insert the dipstick as if you were replacing the
cap and then remove it again. There should now be
oil on the stick. If there is no oil on the stick, or oil
only at the very end of the stick, you should add
oil until the engine crankcase is lled (see “Adding
Oil” portion of the “Maintenance” section).
e. The oil will be visible in the oil ll spout when full.
f. Be sure to replace the cap when nished checking
oil.
Model Number XP20HP
Engine Oil Capacity 40.5 . oz (1.2 L)

7
Changing the Oil
Remove drain plug
Using a 12 mm hex wrench, unscrew the oil drain plug, which
is located on the crankcase underneath the oil ller/dipstick
cap.
Allow all the oil to drain from the engine.
1.
Drain oil
Drain oil into an approved oil disposal container. Contact
your local auto parts store for information on oil disposal.
2.
Replace drain plug
Replace the oil drain plug and tighten with a 12 mm hex
wrench.
3.
CAUTION: Worn out or dirty oil does not cool the
engine properly and can lead to catastrophic
engine damage.
In addition to regular oil changes, it is necessary to drain the
oil from the crankcase if it has become contaminated with
water or dirt.

Routine maintenance of the air cleaner helps maintain proper
airow to the carburetor. Check that the air cleaner is free of
excessive dirt after every use.
CAUTION: Improper maintenance may cause
less air to enter the engine or dirty air to enter
the engine causing overheating and engine
wear.
MAINTENANCE AND CARE (CONTINUED)
Changing the Air Filter
Remove lter cover wing nut
Remove lter cover
Remove old lter element
Remove the top screw located on the top of the air lter cover.
Remove the plastic air lter cover by lifting the cover upwards
to expose the air lter element.
Remove the wing nut on top of the air lter element and slide
lter element o center bolt. This lter is paper and is not
reusable. Please call 1-844-DUROMAX to order a replacement
lter for your engine.
1.
2.
3.
8

9
Replace new lter element
Slide new lter element over center bolt, and replace wing nut.
Tighten wing nut hand tight to keep lter in place.
4.
Replace lter cover
Replace plastic air lter cover over the air lter base.
5.
6. Secure lter cover
Fasten the air lter cover with the air lter cover wing nut and
tighten about hand tight.

MAINTENANCE AND CARE (CONTINUED)
The spark plug is important for proper engine operation.
A good spark plug should be intact, free of deposits, and
properly gapped.
Spark Plug Maintenance
Remove spark plug cap
Remove spark plug
Inspect spark plug
Pull on the spark plug cap to remove it.
Unscrew the spark plug from the engine using the spark plug
wrench included with this product.
Visually inspect the spark plug. If it is cracked or chipped,
discard and replace it with a new spark plug. We recommend
using an F6TC spark plug such as NGK BP6ES.
1.
2.
3.
CAUTION: Improper maintenance may cause reduced fuel economy, misres,
trouble starting, or damage to the spark plug threads.
SPARK PLUG
CONSULT MANUAL
BEFORE REMOVING
10

11
Measure plug gap
Measure the plug gap with a gauge. The gap should be 0.7-0.8
mm (0.028-0.031 in).
4.
Clean and re-gap
If you are re-using the spark plug, use a wire brush to clean
any dirt from around the spark plug base and then re-gap the
spark plug.
5.
Install spark plug
Replace spark plug cap
Screw the spark plug back into its place on the engine using
the spark plug wrench.
Replace the spark plug cap.
6.
7.

Emptying the Gas Tank
Shut fuel valve OFF
Remove carburetor drain bolt
Place funnel below drain port
Turn the fuel valve to the “OFF” position.
Remove the outward angled bolt that is located on the
bottom of the carburetor.
Place funnel with container to catch the gasoline under the
drain port location.
1.
2.
3.
CAUTION: Do not store fuel from one season
to another. Gasoline sold at the pump today
contains additives such as ethanol that even
when stored properly may damage the fuel
system components.
If you have been using gasoline in your engine, before storing
your engine for extended periods of time you should drain
your engine fuel tank of gasoline.
MAINTENANCE AND CARE (CONTINUED)
12

Turn fuel valve ON and drain
Turn the fuel valve to “ON” and allow gasoline to drain into
the container until the gas tank is empty.
4.
Shut fuel valve OFF
Replace carburetor drain bolt
Store emptied gasoline
Once the gasoline is fully drained, move the fuel valve back to
the “OFF” position.
Reinstall the carburetor drain bolt.
Store the emptied gasoline in a suitable place and add fuel
stabilizer to keep fuel fresh and usable.
5.
6.
7.
13

MAINTENANCE AND CARE (CONTINUED)
Store engine
After the engine shuts o and cools, then you can store the
engine.
3.
Storing the Engine for Same Day Use
CAUTION: Do not obstruct any ventilation openings and keep the engine in a cool
dry area.
14
Run the engine
Turn engine switch to OFF
Allow the engine to run for 3-5 minutes.
Flip the switch down to the “OFF” position to shut the engine
o.
1.
2.

Storing the Engine for Use Within 30 Days
Run the engine
Allow the engine to run for 3-5 minutes.
1.
Shut fuel valve OFF and run dry
Turn the engine switch OFF
Add fuel stabilizer and store
Shut the fuel valve “OFF” and allow engine to run until it stalls
out.
Flip the switch down to the “OFF” position to shut the engine
o.
Add fuel stabilizer to gas remaining in tank, and store the
engine.
2.
3.
4.
15

MAINTENANCE AND CARE (CONTINUED)
16
Storing the Engine for Longer Than 30 Days
Shut fuel valve OFF and run dry
Turn the engine switch OFF
Empty the gas tank
Shut the fuel valve “OFF” and allow engine to run until it stalls
out.
Flip the switch down to the “OFF” position to shut the engine
o.
Fully drain your gas tank as shown in “Emptying the Gas Tank”
on page 12-13.
2.
3.
4.
Run the engine
Allow the engine to run for 3-5 minutes.
1.

17
5. Remove spark plug
Add oil to cylinder
Remove spark plug as shown in “Spark Plug Maintenance” on
page 10.
Add 2 tablespoons of 10W-30 motor oil directly into the
spark plug hole, and pull the recoil to lubricate cylinder. After
lubricating cylinder reinstall the spark plug as shown in “Spark
Plug Maintenance” on page 11.
6.
Store engine
The engine is ready to be stored in a cool dry area.
7.
CAUTION: Do not obstruct any ventilation openings and keep the engine in a cool
dry area.

1
2
3
1. Crankcase 11310-Z0D0510-0BA0
2. Oil Drain Bolt 11007-Z080110-00A0
3. Oil Protector 37050-Z010210-0000
Common Engine Parts
4
5
6
7
8
9
4. Oil Seal 90682-Z0J0110-00A0
5. Crankcase Cover 11411-Z0D0510-0BA0
6. Crankshaft Bearing 90547-0208-CLAE
7. Bearing 90548-0202-CLA0
8. Oil Fill Cap/Dipstick 15010-Z080130-Q500
9. Crankcase Cover Gasket 11001-Z0D0110-00A0
COMMON ENGINE PARTS
18

10. Valve Cover 12410-Z0D0210-0BA0
11. Breather Tube 17004-Z0D0410-00A0
12. Valve Cover Gasket 12004-Z0D0211-00A0
13. Muer/Cylinder Head Gasket 18101-Z0D0110-00A0
14. Spark Plug 30010-Z010210-00A0
15. Cylinder Head Gasket 12131-Z0D0310-00A0
16
17
18
19 20
18
21
16. Crankshaft Assembly 13300-Z0D0210-CLTM
17. Piston Rings 13200-Z0D0110-00A9
18. Pin Clip 13122-Z100110-00A0
19. Piston 13111-Z0D0211-00A0
20. Pin 13121-Z1X0110-0000
21. Connecting Rod 13010-Z0D0311-00A0
19

22. Ignition Coil Assembly 30400-Z190210-0000
23. Charging Coil Assembly 30140-Z160230-0000
24. Camshaft Assembly 14200-Z0D0410-00A0
25. Recoil Assembly 28200-Z710110-BG00
26
27 28
29 30
31
26. Spacer/Cylinder Gasket 17002-Z0D0210-00A0
27. Carburetor Spacer 16003-Z0D0210-00A0
28. Spacer/Carburetor Gasket 16001-Z100110-00A0
29. Carburetor Assembly 16100-Z0D1210-00M0
30. Carburetor/Air Filter Gasket 17001-Z0D0110-00A0
31. Gasoline Fuel Line 90686-Z520110-00M2
COMMON ENGINE PARTS (CONTINUED)
20