Why does my bike have problems downshifting. Sometimes i can't shift all the way down until I give it gas

SOURCE: honda shadow aero 2005 VT750C shifting problem

You have a bent shift fork. This is not a repair job for the amateur. The engine comes out of the frame, turns upside down then the bottom of the gear case gets separated from the top. The entire shift drum, forks and all, gets removed and the bent fork gets replaced. The engine re-assembles in the reverse pattern.

Now what about stressed gears? Any cracked or broken slider gear dogs?

You are going to have at least 75 parts on the work bench. Was the collar on the slider gear on the left side or the right? I am trying to show you why you had best be careful. The shop charges more to fix a box of loose parts than if they fix a gearbox.

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SOURCE: C90 HARD TO SHIFT DOWN FROM THIRD GEAR

You have a bent shift fork. The repair means taking the engine out of the frame then removing the top end, removing the flywheel and electrics, removing the clutch , shift mechanism and kick starter and a few other parts. THEN you are ready to split the gearbox to remove the crankshaft and then the bent shift fork. Next you get to put it all back together. This is a pretty big job for the home mechanic.

You will need an impact driver, flywheel puller, case splitter and torque wrench plus the normal screwdriver, pliers, etc.. Alternate to the special tools is taking it to the dealer and say "Fix it".
I normally tell people to take it to the shop just so they don't get into such an involved project.

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SOURCE: My sons klx 110 grinds when downshifting

While sitting still the gears are not moving. This sounds like a slightly bent shift fork. In the diagram below the slider gear moves left and right to engage the gears. The gear "dogs" fit into holes cast into the stationary gears. The grinding takes place as the fork moves the slider into first gear but the dogs are not getting moved the full distance needed to fully engage the gear because of the bent fork. The center case must be split to gain access to the gears and shift forks.

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SOURCE: 97 Honda Odyssey Auto transmission downshifts

Try checking your timing to solve the ping problem, your timing might be too far advanced. For the downshifting problem, I have this same issue on my odyssey, On the top of your efi manifold you will see 2 wires that control your throttle, One of them extends to the transmission and basically lets it know when you are pressing firmly on your gas pedal, telling it to downshift. I would adjust it so the cable has some more slack in it, therefore requiring a harder press on the pedal before downshift, and hopefully a sooner upshift. You can also slightly adjust idling problems if the van is running high while in park or drive while sitting. As for the gas vapor purge code, I would first try replacing the egr valve, its only a couple bucks and takes no more than 5 minutes.