Reddit mentions of Mikuni DF44-227 Genuine Single Fuel Pump

Seems like maybe the stock vacuum pump cant keep up with the bigger bore. They included one, but I'd chuck theirs, and switch back to your regular stock one. If it persists, the DF44-211-D pump is what most people opt to switch to when it becomes an issue.


A genuine Mikuni one is only 29$, but there's some off brands for around 15 if you want to cut back the budget. That said, it's a good part to buy quality of. Is a awful feeling when your bike dies mid-road cause the vacuum pump is intermittently working, or cant keep up with the engine under extended full throttle.
https://www.amazon.com/gp/product/B000GTV9AK/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1


I'd also advise jetting up slightly, but if you're on the stock airbox and carb, it might be fine with how a lot of scooters build limiter chokes into their intakes. Which lets them run it leaner for better fuel economy. Though, the common stock 50cc 4 stroke carb tends to be sealed shut- and therefore the jets unreachable unless you want to drill out the studs they put in place of screws.


Really it sounds like a fuel issue, and not a timing issue if you've already set it during install. I'd still check it for peace of mind, but it's more likely either the pump or the carb- the pump being the cheaper of the two, and helpful whether it is or isn't (most people switch to it anyways, even without a bore).


hmm what else..... you're running the highest grade pump gas you can get right? Scoot engines tend to be high compression and high RPM to compensate for being so small. Both of those things need a higher octane to run stable. If you put in 85-88 (US regular), it may run, but you'll have issues on most scooters doing so.