While I am not familiar with that particular motor, there are only two ways to change the oil in small motors. You either have drain plug on the bottom of the engine and a fill / level plug on the side, or you have to tip the engine up and drain it through the filler hole. The 2nd one is not very convenient, but some motors do work like that. I have a Honda motor that needs to be drained that way.
Hey the GX390 engine oil capacity is just a little over 1 quart of oil you have to place the engine on a flat surface to verify that the oil is at the correct level, if your engine has a big dipstick it has to be filled to the lip where you pour in the oil or if it has a small and long dipstick check for 2 dots and fill to the upper dot.
Yes, it is needed to set the depth of tilling, longer the bar is set the higher the tiller rides. The lower the bar is then the deeper the tiller tries to till.
The bar also helps you manoeuvre the tiller left and right. If you look at the owners manual you can see what it looks like and get one made if it is lost. It will work without the bar but it adds control when rotovating.
an example would be if the ground is hard or it finds some stones the tiller can buck about until breaks through the soil or it removes the stone from its path.
pushing down on the handlebars presses the bar into the soil, the bar lifts the tiller blades from the ground and it will settle down. Without the bar it wil buck until you pull it back away from the stones or into some softer ground and it can start munching into the soil again.
First, I'm not a Honda mechanic.* Check warranty. Call for service.*** Following for information only.**** Of all the vids I've listed below I was wondering why no one mentioned a fuel filter. Manual; https://powerequipment.honda.com/support/owners-manuals/lawn-mowers/hrmBut I couldn't find one on quick glance at manual. Normally this is the first thing I check on any gas motor. (even cars) Water, soil, and old fuel clogs stuff real fast. Especially motors that sits around for months without movement or use. Most of the vids take stuff apart right away. But I would look at the last one "Basic Maint Checks" first and go from there. Caution; most are technical in nature so if your not a novice mechanic then I would suggest calling someone qualified to work on Honda's or at least a small motor clinic. (we have a "Swap meet" guy that has "magic touch" with gas engines.)* Honda (old) won't stay running; (cleaning main jet); https://www.youtube.com/watch?v=JZLrHXMtYGU* Honda won't start (troubleshoot method); https://www.youtube.com/watch?v=MW1YgUKh1Tw* Another old model won't run; https://www.youtube.com/watch?v=rbiaeZDI6N8* Red top model; https://www.youtube.com/watch?v=2rLB3KmrGsQ* Detailed take apart; https://www.youtube.com/watch?v=wlyYYrfyjdI* HM215 dies (and runs really rough); https://www.youtube.com/watch?v=E7lmvsybUvQ* Basic maint checks; https://www.youtube.com/watch?v=HrhNgXF7ag8* Check your warranty, call for service.Aloha, ukeboy57Update: 07/10/2018 Jim replied that He found (the shop did)a weak or partially shorted out ignition coil. Wow, This used to be a common problem with the old pull to start mowers way back in the 50-60's. Bad coils were common as they were hand wound and open. Modern coils are usually encased in plastic to prevent water from entering wire winding. I'm wondering where they are getting coils from?* Oh, Tip;Hard starting engines can be easily started by using "Engine start" spray (carberator cleaner)as they sell it at NAPA,Walmart, etc. You can find a lot of vids on how to start a generator that has been sitting around. No need to remove spark plug. Just a shot into the intake will do the trick. (Spray will also clean the plug if you do happen to pull it out to check.Aloha, ukeboy57