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Any news?

No good news to report, Karl.  Still having the issue, despite continuing to sort it out.  I think I'm gonna have to let a reputable KYMCO dealer have a crack at it.  For the time being, since we're starting to get much colder here now, I just gonna ride it over the winter from time-to-time and see how it does running with colder temps.  I even talked with a KYMCO tech down in Spartanburg and he stated it could be a number of things, which would likely be best sorted-out by a knowledgeable dealer service tech possessing the proper testing equipment.  I'm done messing with it for a while...very frustrating.  My suspicion is that it is something wonky within an electrical component, maybe the ECU or a bad sensor, for a couple of examples.  I imagine it's gonna be an expensive diagnosis, especially with no codes showing-up, and subsequent repair down the road.  It's gonna be beyond difficult to get rid of it with it running the way it does now, so probably gonna have to just bite the bullet and take it to the dealer.  Until then, I'll be anticipating what the heck is going on with it.  I'll post up on here when the problem is finally revealed to me from the dealer.  Thanks for all your help, Karl, as well as any others who replied.

If cap is vented, hole should be clear.

According to "Crossbolt", fuel cap is not vented.  Perhaps the tank is vented elsewhere.  The hesitation problem persist with the fuel cap loose though, so that likely rules-out that being the issue.

I'm on my 2nd tank with fuel system cleaner mixed in the tank, but no improvement to this point.  I put about a 1/2 ounce of Lucas Tune Up In A Bottle (Upper Cylinder Lubricant and Injector Cleaner) per each full tank. 

I was telling "Crossbolt" that there was too much oil in the scooter when I first got it, so I drained-out about 6 ounces to get it to the proper level on the dip stick.  So, I am wondering if that situation may have contributed to the hesitation issue in some way.  There was no oil in the air box and the filter element is clean.  The plugged drain tube connected to the air box didn't have much oil in it either, but I drained-out what little there was in the tube.

Thanks, John!

I do believe the vent valve is buried below the gas tank behind the radiator. At the very least it will take literally HOURS to get to it. I even was sent a replacement valve but sent it back when I saw how much plastic body panels had to be removed to get at it. That's when I drilled a hole in the cap.

 

Yeah, getting to that vent doesn't sound fun at all.  I don't blame you for sending the part back and opting to just vent the cap yourself.  If this is a common problem with these scoots, sure wish somebody would make a video of the cap venting mod and put it up on YouTube.  Anyway, I have to go get a key made at the local key shop so I have an extra key for the scoot, as I don't have the extra key for it at my current location.  I'll be back in-touch soon afterwards to see if that is even the issue.  Thanks, Karl.  I really appreciate your help with this.

The standard cap is not vented. That vent is SUPPOSED to be vented by a vacuum valve scheme but that cheapo valve sticks sooner or later on ALL brands and models. I have a post way back how I vented mine but the pictures are gone. I am willing to take mine apart and post new pictures if you want, if that is your problem.

I can't specifically say that is the problem, Crossbolt.  It was just suggested I check the gas cap by John Grinsel.  I wish I knew what the problem is, but at this point, I'm still troubleshooting.  Do you have the same gas cap I have, except that you vented yours?  Thanks!

Since bike is 2013 with only 6,000 miles---which means it spent a lot of time sitting---I would check gas tank,(clean it)  fuel lines and clean  injector---before getting into computer junk, even gas tank vent/cap needs checking.

Thanks, John!  All good ideas.  How do you recommend checking the vented gas cap?

Check valve adjustment.

Checked and adjusted the valves back to spec, John.  Unfortunately, that apparently wasn't causing the running issue, which is hesitation during acceleration.  I am going to investigate the map sensor next, which according to a post I read on here, could be an issue.  If you have any other suggestions, please advise.  Thanks, John!

I have recently gotten a 2013 KYMCO Downtown 300i w/about 6,000 miles on it that has some concerning hesitation most noticeable between approximately 25-45 mph.
I can power through the hesitation and it seems to run fine.  Have any of you other Downtown 300i owners ever experienced this particular issue?  If so,
any recommendations on what to check and/or what might be a solution to restore consistent, smooth acceleration?  Thanks in advance for any help.

SOLD!