Why generators show "engine lacks power": 174 documented causes and brand-specific fixes, compiled across 14 manufacturers.
Dirty air filter
5 brands- Cummins/Onan: Replace air filter; Replace air filter.
- Dayton: Replace air filter
- Echo: Clean or replace as needed
- Firman: 1. Don't Overload Generator 2. Replace air filter.
- Generac: 1. Reduce load (see Know Generator Limits). 2. Clean or replace air filter. 3. Contact IASD.; 1. Reduce load (see “Don’t Overload the Generator”). 2. Clean or replace air filter. 3. Contact Authorized Service Facility.
Load is too high
3 brands- Dayton: See "Specifications" on Page 5 for wattage/amperage capacity
- Firman: 1. Don't Overload Generator 2. Replace air filter.
- Generac: 1. Reduce load (see Know Generator Limits). 2. Clean or replace air filter. 3. Contact IASD.; 1. Reduce load (see “Don’t Overload the Generator”). 2. Clean or replace air filter. 3. Contact Authorized Service Facility.
Dirty air cleaner
3 brands- Bgm/Nhm: Replace air cleaner
- Cummins/Onan: Clean or replace air cleaner.; Replace air cleaner
- Marquis: Replace air cleaner
Restricted fuel flow due to plugged fuel filter
3 brands- Bgm/Nhm: Replace fuel filter
- Cummins/Onan: Clean fuel filter; Clean fuel filter.
- Marquis: Replace fuel filter
Exhaust system blocked or restricted
3 brands- Bgm/Nhm: Locate and remove cause of blockage
- Cummins/Onan: Locate and remove blockage, clean spark arrester screen; Locate and remove blockage, clean spark arrester screen.
- Marquis: Locate and remove cause of blockage
Excessive engine wear or damage to engine
3 brands- Bgm/Nhm: See Engine Block Assembly section
- Cummins/Onan: E140H engine: See Onan Elite Horizontal engine manual 965-0758; GH170, GH280 engines: See Engine Block Assembly section; See Engine Block Assembly section
- Marquis: See Engine Block Assembly section
Faulty ignition due to incorrect spark plug gap
3 brands- Bgm/Nhm: Reset spark plug gap
- Cummins/Onan: Reset spark plug gap; Reset spark plug gap.
- Marquis: Reset spark plug gap
Restricted fuel flow due to faulty fuel pump
3 brands- Bgm/Nhm: Test fuel pump and repair or replace if faulty
- Cummins/Onan: Test fuel pump and repair or replace if faulty; Test fuel pump and repair or replace if faulty.
- Marquis: Test fuel pump and repair or replace if faulty
Incorrect fuel mixture due to incorrectly adjusted fuel mixture screws
3 brands- Bgm/Nhm: Adjust carburetor main and idle adjustment screws
- Cummins/Onan: Adjust carburetor main and idle adjustment screws; Adjust carburetor main and idle adjustment screws.
- Marquis: Adjust carburetor main and idle adjustment screws
Incorrect fuel mixture due to incorrect float level
3 brands- Bgm/Nhm: Adjust carburetor float level
- Cummins/Onan: Adjust carburetor float level; Adjust carburetor float level.
- Marquis: Adjust carburetor float level
Incorrect fuel mixture due to dirt in carburetor
3 brands- Bgm/Nhm: Disassemble carburetor and clean all internal passages. Replace fuel filter
- Cummins/Onan: Disassemble carburetor and clean all internal passages; Disassemble carburetor and clean all internal passages.
- Marquis: Disassemble carburetor and clean all internal passages. Replace fuel filter
Incorrect fuel mixture due to vacuum leak
3 brands- Bgm/Nhm: Repair vacuum leak
- Cummins/Onan: Repair vacuum leak
- Marquis: Repair vacuum leak
Incorrect valve tappet clearance
3 brands- Bgm/Nhm: Adjust valve tappets (see Engine Block Assembly section)
- Cummins/Onan: Adjust valve tappets (see Engine Block Assembly section); Adjust valve tappets (see Engine Block Assembly section).
- Marquis: Adjust valve tappets (see Engine Block Assembly section)
Carburetor air preheater set incorrectly
3 brands- Bgm/Nhm: In hot weather, place air preheater in summer position
- Cummins/Onan: Check automatic preheater setting.; In cold weather, place air preheater in the winter position
- Marquis: In hot weather, place air preheater in summer position
Combustion chamber deposits
3 brands- Bgm/Nhm: Clean combustion chamber
- Cummins/Onan: Clean combustion chamber.
- Marquis: Clean combustion chamber