Serial No: MAGA-1183915
Thanks,
Honda issued a Service Bulletin to address this problem. The fix is to replace the throttle lever with an updated design that has more durable materials. This is a "fix-as-fail" repair, meaning Honda will replace the lever on mowers with the problem that are still under warranty. This serial number was registered in 2006, and the warranty expired on 9/21/2008.
Without inspecting and confirming it is indeed the problem, it's hard to say for absolute sure this is the solution, but if you are up for some DIY repairs, the part is pretty cheap ($2.08 list price) and not difficult to replace. An experienced tech could do it in less than 20 minutes, but you may want to budget 45-60 for a first-time effort. Let me know, and I'll send you the detailed instructions. Caveat: Replacing the lever requires adjusting the throttle cable, and to do so properly, you need a tachometer to correct set the engine speed. A feeler gauge is also need to properly set the choke control gap too.
The part number for the updated throttle lever is 17851-VA3-D01. Google the part number to find a Honda Dealer selling it online, or use this link to find a Honda Dealer in your area:
Find A Honda Dealer
If you'd rather take it to a dealer, most would bill you the flat-rate for this job, which is 0.6 hours x their hourly shop rate. So if they bill at $60 an hour, expect labor charges of about $36 or so, plus the cost of the part. Every dealer sets their own policy and rates, so this is just an example, not a promise or quote.