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Honda GX670, GX620 2007 User Manual – Factory Specs for LPG/Natural Gas Engines

Right, let’s talk about the Honda GX670, GX620 2007 User Manual. You’ve got one of these LPG or natural gas engines on a welder, pressure washer, or maybe a commercial mower. The aftermarket manual you found online skipped the fuel regulator specs, didn’t it? I’ve seen that happen. This is the 2007 factory User Manual, 48 pages, straight from Honda. No copy, no reprint – original OEM print. That matters when you’re setting the governor or checking the Oil Alert system.

Page 2 carries a warning that engine exhaust contains chemicals known to cause cancer, birth defects, or reproductive harm. You need to read that. Page 4 tells you how safety messages work – DANGER, WARNING, CAUTION. These are not suggestions. Aftermarket manuals leave that out. This one doesn’t.

Fuel System: Governor and Regulator Setup

The Fuel section under CONTROL & FEATURES covers the governor, the fuel regulator, and the LPG system. If you’re swapping a carbureted unit to LPG or diagnosing a lean condition, the factory settings for the GX670 and GX620 are in here. The manual explains the Engine fuel system from the tank through the regulator to the mixer. You won’t find that in a generic small-engine book.

Oil Change, Filter Service, and the Oil Alert System

Every GX620 and GX670 has the Oil Alert system – it shuts the engine down if oil pressure drops too low. The manual shows you how to test it and how to reset it after an oil change. Pages for the oil filter change procedure include the correct filter part number and the torque spec for the filter housing. I won’t print the number here because you need to look it up in the manual, but I will say: aftermarket manuals often get the thread pitch wrong. This one doesn’t.

Before Operation: Is Your Engine Ready to Go?

The BEFORE OPERATION chapter has a checklist: oil level, air filter, fuel connections, battery for electric start. Honda printed this so you don’t skip steps. Check the fuel lines for cracks – LPG will eat rubber that isn’t rated for it. The manual lists the required fuel for LPG and natural gas. Don’t mix them up.

Servicing Your Engine – Maintenance Schedule and Oil Recommendations

Maintenance is where most DIYers get into trouble. The maintenance schedule on page 23 (approximate) tells you when to change oil, replace the spark plug, service the air cleaner, and inspect the spark arrester. Oil recommendations are 10W-30 for most temperatures, but the chart covers 0°F to 100°F. The manual specifies API service category SJ or later. That’s important for the GX670 because it’s a heavy-duty engine. If you use the wrong oil, the Oil Alert might trip early.

Troubleshooting: Engine Will Not Start or Lacks Power

The TAKING CARE OF UNEXPECTED PROBLEMS chapter is two pages. It lists causes for no-start and low power: fuel supply, spark, compression, air filter. The LPG system has a fuel shutoff solenoid – the manual tells you how to test it with a multimeter. Wiring diagrams for the electric starter and battery connections are in the TECHNICAL INFORMATION section. That’s where you find the serial number location too. Related manuals like the Honda GX670 2005 Parts Catalog will give you exploded views, but this User Manual is for operation and owner maintenance. For a car, you might grab the Honda Civic Sedan 2012 User Manual – OEM Shop Manual or the 2016 Honda CR-V User Manual – OEM 532-Page Owner’s Guide – same philosophy: factory or skip it.

Technical Information – Specifications and Wiring Diagrams

The back of the manual has specifications: displacement, net power, fuel type, oil capacity, spark plug gap. For the GX670, the spark plug gap is 0.028–0.031 in (0.70–0.80 mm). The wiring diagrams for electric start and battery connections are clear. If you’re retrofitting a battery, this is the page you need. The manual also covers carburetor modification for high altitude operation – yes, even on LPG. That’s the kind of detail aftermarket docs get wrong. For a broader sense of OEM reliability, take a look at the Automotive Industry Overview – Honda’s approach mirrors that: everything documented, nothing guessed. You can also check Automotive Industry Overview.

FAQ

Does this manual cover the GX620 as well as the GX670?

Yes. The cover says GX620-GX670. Both models are covered in the same 48-page manual. Differences like displacement are noted in the specifications table.

Why is an OEM manual better than a third-party reprint?

The OEM manual comes from Honda. It has the exact fuel regulator settings, Oil Alert system test procedure, and wiring diagrams for the electric starter. A reprint often has faded diagrams or missing pages. More than once I’ve seen a reprint skip the safety page. Page 2 of this manual has the California Proposition 65 warning – that’s a legal requirement if you’re in California. A reprint won’t have it. You’re paying for accuracy, not a photocopy.

You need this manual on your bench next time you touch a GX620 or GX670. Don’t rely on a forum or a scanned copy from 2006. Access the Factory Manual from AutoRepairManuals, print it out, and keep it with the engine. That’s what Honda intended.