Rotax DD2 - Not starting

Hi, so I’ve got a Rotax DD2 Kart (Pre Evo) changed the gearbox oil the other day, go run it, will not start now. Pretty sure it’s not the gearbox oil causing the non-starting issue, thought maybe a coincidence, then started to see air bubbles in the line from the fuel pump to the carb, disconnected it all, just for good measure, put it all back, primed the pump, now fuel isn’t actually making it to the carb. Swapped out the fuel pump for a new one, still not starting. checked the spark plug that’s working, the battery is fully charged, they are basically brand new, the fuel pump is new as stated before, there is still an air bubble in the line from the pump to carb…the starter motor is making quite a loud knocking sound, so unsure if its that right now.

When starting, still doesn’t look like fuel is moving into the carb, but thinking that maybe because it hasn’t started yet.

Link to video of what happens when are trying to start it.

Any help would be great, cheers Matt.

The fuel will need to fill the float bowl in the carb before it will fire. Have you primed the system? You can prime it by blowing into the vent pipe on the fuel tank. If you find that the fuel won’t flow while trying to prime it I’d suspect the float and or needle in the carb may be stuck.

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easy way to see if your getting fuel is to remove air box and cover carby with hand , wind over and hand should be wet with fuel