Buddy 125 not accelerating, dying

[k.fredrickson]

I have a 2009 Buddy 125 that I just got back from the shop. It's been there for 4 weeks, while they tried to diagnose why it wasn't starting and then why it wouldn't "run right". I've had it for 2 years now and it's always been a bit sluggish when it first starts. The shop got it running, drained fuel, did oil change, replaced the carburetor (they thought this would fix all the issues because when the took it apart to clean, it was missing a part from the previous owners bad clean/put back together job) but it seems to be running the same, if not worse when it first starts up.

Driving home from the shop: about 42 degrees out, ran ok leaving, but accelerating away from the first light I had to sit at, it struggled to get above 5-8 mph. I thought I would have to pull over because I was impeding traffic flow. Letting off and then back on the acceleration, I was able to get it to rev up again to actually drive 30-35 mph. The rest of the way home (about 5 miles) it drove ok. One other instance of it putting along like that after stopping at a light.
Yesterday: I had filled up the tank and drove it for about 25 mins (10 miles).
Today: driving it to work, it was 52 degrees out. It started fine, I took the back roads to the main road in order to give it a chance to not accelerate, which it did several times. I got it up to 35mph just before hitting the main road so I thought I was over the initial bogging down. Nope, just after accelerating from a stop light, it struggled to even go 5 mph and then died. I sat on the side of the road for 2 mins idling/reving the engine until I thought it might actually drive enough to get to work (I've gone about 1/2 a mile by this point, 4.5 miles to work). I got it to go ok through the next light and then it bogged down again a bit, but then by the 1 mile mark it was driving fine. It drove fine the rest of the drive and I sat at several lights and then accelerated from a stop many more times without issue.

So any suggestions for what to check/may be wrong. The shop I brought it to is Scooterville in Minneapolis, so they're very familiar w/this model. The tech had about 13 hours of troubleshooting it, he swapped out the CDL, ran a fuel IV to bypass the fuel line, swapped out coils, spark plugs, in addition to the items above and could not find the issue. I guess I'm baffled that a shop pro can't figure out the issue, but I thought I'd check here before I write the Buddy off as a loss and sell it for way less than I paid. Also, it was never this bad the first two summer's I drove it. It quit starting consistently last fall and then wouldn't start at all this spring.

[k.fredrickson]

Tech at Scooterville also checked the exhaust system, took it off, cleaned it in case there was any blockage. I believe he checked the fuel filters as well. He rambled off a long list of things he did to troubleshoot so I'm trying to remember them all. He basically said that if I ever figure out the issue, to let him know because "after working on hundreds of scooters, this one has him stumped for the moment".

[dasscooter]

Did he check the valve adjustment? Although extremely rare, you could possibly have a burnt exhaust valve. This would cause it not to seat correctly and cause a lack of compression and therefore no power.