First 125 and no idea what’s wrong

[Lukej90]

Hi, just getting into bikes, I bought a 2017 mutt mongrel 125, bliss for a couple of weeks and Monday evening it decided it would start to backfire extremely loud, and vibrate in higher rpms. Since that happened the exhaust has got louder, and deeper sounding, the revs fluctuate on their own and it’s sluggish. I’ve checked spark plug, bone dry and clean, new battery, all hoses and wires clean and correct, any ideas on what to check first?

[stinkwheel]

First thought is your exhaust has come loose or is leaking somehow.

When you say it backfires, when does it do this? A classic symptom of a leaky exhaust is popping and banging on the overrun (so when you've been riding along then close the throttle).
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Nobby the Bastard]

If the exhaust has got louder I would.... check the exhuast is still connected correctly...
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[Lukej90]

Exhaust is connected corrrectly, had a new gasket prior to my owning, checked for leaks and nothing. Backfiring happens anytime, changing up gear, over run, even just starting

[Nobby the Bastard]

Have you taken the baffle out?
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[Lukej90]

No, standard exhaust, happened whilst riding, and it has been cutting out a lot previous

[Easy-X]

Double check the air box and filter are all connected/seated. After that I'd probably check the fuel is flowing correctly but I'm not familiar with that particular bike. Older bikes you'd just pop the fuel hose off the carb, into a jam jar and open the petcock then eyeball the fuel flow.
____________________
Royal Enfield Continental GT 535, Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[Lukej90]

As far as I’m aware engine is a Suzuki gn125 replica, fuel injected

[WD Forte]

Engine is K157FMI a GN125 clone to euro 4 spec as used on a shit ton of other chinese made bikes
Mutt just bolt on hipster cosmetic stuff to make it more 'cool'

As its EFI the first step should always be to get an OBD reader
and check the fault codes
____________________
bikers smell of wee

[stinkwheel]

A tight tappet would do it too. Should be an easy visual check of the clearance, or a compression test if you've got a compression tester.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[struan80]

Nice looking little bike. Hope you get it fixed soon.