My son's '17 Ace is so nearly identical to his sister's that their VIN numbers are almost the same but that is where the similarities end. My son's has always slightly lacked the power of his sisters and his machine has always been more difficult to start weather it's cold start or hot start. The last couple runs out we go real well, then on a hard push, most often in steeper terrain, his machine (I THINK) acts like its either out of fuel, or has a fouled fuel filter and although I have not checked the filter, a plugged or fouled filter would display regardless of conditions. We can run for HOURS without issue in easy riding but there are a couple tough hills on the main trail to our riding area and that is where his problems are. I can see him start to lose speed and then he's done. I'm in my 900 so I can't hear what his ride is doing and the way he explains it to me....can't be replicated into real words...LMAO
To make matters a bit more "Challenging", my son is Autistic. He is high functioning, but not very effective at communication and of course being an Ace I can't ride with him to see exactly what happens and my knees are so bad I can't spend much time in the seat anyhow.
Nearest I can gather is it sounds to me like a bad fuel pump. It will give it enough power to run easy, but starves the engine on a tough pull, but not always on a tough pull, and the performance (or lack therof) is unpredictable so for as many times as I have tried I can't make the machine fail myself. Would a faulty fuel pump also explain why it has always been a tough start. Am I close?