Small Engines (Lawn Mowers, etc.): Honda surge, surge

Question
I have a Honda GXV530 EXA2 GJARM1011691 on a Craftsman rider. The engine surges at full throttle, but idles OK. I've replaced the carb, fuel filter, checked the fuel pump output, and fuel lines for obstruction. I set the RPM at 3400 (Mfg. spec.)I've also checked the float level per mfg. instructions. It surges with or without the blades engaged. I've sprayed starting fluid around all gaskets around the intake to check for vacuum leaks. I've been working on small engines for 20 years, but don't have much experience on Honda. Any help would be appreciated.
Thanks,
Keith

Answer
Keith:

Hunting and Surging is one of those problems that can drive us technicians crazy.  Unfortunately there is no single answer to resolve the issue.  I deal with hunting and surging all the time in my everyday life.  It seems the stricter the EPA/CARB guidelines become the more the engines tend to hunt and surge.

FWIW, there have been times when i have been at the engine factories in Asia and have watched them start and run an engine and it runs perfectly.  I have personally drained the fluids out of that engine, boxed it myself and when it arrives here in USA the engine surges!  Go Figure!

It could be an intermittent spark problem caused by a bad low oil switch or ignition coil. Unplug the oil switch if so equipped.  If problem is resolved, check oil level or for a bad oil switch.

With an inline ignition tester check and see that you have consistent spark. If you don't you will need to replace the ignition coil. Before you do that however look inside the spark plug boot and you will see a slot that a straight blade screw driver fits into,  loosen that up, remove and check the diode too...(ONLY IF YOU HAVE INCONSISTENT SPARK)

Isolate the engine from the rider by disconnecting the ignition ground wire on the rider.  If your problem goes away you may have a safety switch/ignition switch-shorted wire etc giving you grief.

Or it could be a governor related problem.  With the engine running full speed grab the gov rod and hold it with a pliers.  If the problem goes away you need to start looking at the back spring, fine regulating spring, pulling rod etc.  you may try hooking the spring in the different holes on the gov arm.  These springs cant be kinked, stretched, distorted etc or hunting and surging will occur. If all this fails it could even be the gov gear itself which is located inside the engine. (I doubt it, but its always a possibility)

You may also try increasing your RPM to 3600.

Let me know what you find

Dave