Server Maintenance

Good day everyone!
I am pretty new to ATV/UTV/Small engine repairs and would like input on your absolute must-have specialty tools for maintenance and repairs. Aside from the obvious wrenches and sockets, what are some more specialty type tools you use for troubleshooting? I don't plan to open a repair shop or anything, I just do this as a hobby. Looking forward to your responses!

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Hi, I'm a newbie on here.  I just got a 2007 Suzuki KingQuad LT-A450X.  Are there any specific issues to look for on this model?  Any specific maintenance to do other than the usual oil and filter changes?  
Thanks

I pulled out my Big Bear needed to do a few things probably havent been started in a year. Gassed it up charged the battery started right up. I have been using it around the property for this and that. Went to hook up my trailer to pull up to the house while it was idling it quit. Went to start it turned over but wouldnt start. After trying a few more times lost all power. Pulled it up to the house with the John Deere, the first thing i checked was the Universal fit soloenoil from Amazon and it was only a 10 AMP fuse so it does not universally fit the big bear it should be 30 AMP fuse. At the time i remember noticing it but forgot, at the time i had other problems like wiring harness being in a box stuck engine and no spark. when i bought it, yeah i know, thats one ishould have walked away from, but if i go to the trouble of hooking up my trailer and going there, its following me home.
Thats old news, i still need to check it all out see if it lost spark and see if the starter shorted out it was acting kind of sluggish, i replaced the fuse with the spare 10 amp and blew immediately. I will try a 30 and see what happens.

Howdy, look forward to all knowledge available here