OK - Here is an example, I had a Lawn Mower brought to me that the owner kept complaining that it would start on occassion but usually would break the starter cord, and Not start. Too funny.
So I looked at it and right away, I knew it was probably the flywheel key had sheared, so the first thing I always do with almost all engines especially old ones that looked like someone dug them out of the dump, but they all say its their mower or chainsaw, etc. Is that I high pressure power wash them down, using some purple power cleaner, and then wait for them to dry in the sun. Lol.
I don't like the grime, grease, oily mess, so before I touch them they are fairly clean with Purple Power cleaner, and I also want to be able to see if all the parts are intact and Not broken or missing (I have had lots of them, that were missing parts from a homeowner trying to take it apart themselves). , I get the purple power cleaner at the dollar store, and costs about $4.00 a gallon (but I use less than a quart per engine). I also dump the oil out into a recycle container, and dump the gas out too looking for dirt & debris, also Inspect the oil especially on 4 stroke engines, and look for metal slivers and metal parts like half a connecting rod or something of the sort. Too funny.
After Inspection, and pretty sure it only needed a flywheel key, I gave the owner a price of $15.00 for parts, and that would include a complete tune-up too. So parts: flywheel key aprox. 50 cents, Spark plug: $2-3.00 depending on which plug I need, I always try to put OEM parts back into the engines, but fuel filters & air filters, some other small parts sometimes use Aftermarket which I buy in bulk,. Anyhow it also needed a long starter cord because the pull was back at the handle for this lawnmower aprox. $3.00, I believe I also put a new foam air filter in the air cleaner for aprox. $1.00. Added a quart of oil back into the engine, aprox. $3-4.00 and when I'm all done the parts came to about $15.00. Oh also needed a little fuel to add back into the tank aprox. $1.00 worth, also completely clean the carburetor, sometimes they need a new bowl gasket too. Anyhow when I'm done it looks and runs like new. I returned it to the owner, and the owner was so thrilled to get their mower fixed and running for $15.00 that they usually end up giving me a tip or a little extra. I also suggest that they bring it back next year for another tune-up, and may suggest they need other work down the road, like replacement fuel lines, etc. etc. If I see anything obvious, which I will also show them.
Again remember this is for friends, neighbors, and family, and I really enjoy working on these engines but I do need to limit myself because sometimes in the summer time, I can have 4-5 of these piling up each week for repair. Also remember for me its just a fun hobby, and I really don't mind spending the time to get them working again. Oh back to the $15.00 Lawn mower repair & tune-up & blade sharpened. I cut my own lawn with it when I was done (too funny - testing it). The friends gave me a $30.00 tip, on top of the $15.00 for parts. On some simplier projects, I have had individuals that just have a hard time starting their chainsaw, and just need some directions on how to get it started, and Not pull the starter cord 20 times or more, also Lol.
But again I could Not do this for a Business, I would have to charge 3-4 times that amount. I also end up with lots of experience and knowledge, that is my reward. I work at my own pace Not the customers, however on occassion I have returned the small engine on the same day. I always show the Individuals that their equipment is now running, and has been repaired. I have been doing this for several years, and get lots & lots of happy return customers with new projects, and I have only had one complaint in several years of doing this. I have learned how to take care of all of my own yard & lawn equipment as a result of fixing all of these engines, which also is a great benefit to me since I can fix it myself, that was also my motivation into why I starting fixing small engines. I have been retired from a full time career of over 38 years at one job, and have been retired now for aproximately 12 years, so I also realize I am getting Old, and Don't need another career or business. Lol.
I enjoy most the analytical diagnostics, and troubleshooting to find out what is really wrong with these engines, or what was the real root cause analysis. Lol & the repair is just secondary to the fact that it can be fixed.
Sorry to be so wordy, but it really is my passion. Lol