HELP! My Tracer 9 stalls when the fuel cap is closed.

[EMINEM]

https://youtu.be/wDbwmUJtDOU (I don't know how to insert video here.)

As you can see in the video, my Tracer 9 drops RPM and stalls sometimes when I accelerate only at the start of the day.

So I opened the fuel cap and tried then it worked perfectly.

What should I do now?

Edited June 11 by EMINEM

[warrior]

More info would help, how much mileage?

It looks like an 'idling' issue, so that tells me that it could be throttle bodies are out of sync.  Depending on the mileage, that's what I would check.  

[EMINEM]

4 minutes ago, warrior said:

More info would help, how much mileage?

It looks like an 'idling' issue, so that tells me that it could be throttle bodies are out of sync.  Depending on the mileage, that's what I would check.  

Edited.

I'll check it out then. 

Thanks!

[2and3cylinders]

There are two hoses coming out of the bottom of the tank

One is the fuel overflow and the other is the smaller tank vent that exit out the left side in front of the chain counter shaft sprocket cover and down.

Make sure the end of vent hose is not blocked or kinked above at some point. 

You can also attach a long larger hose over the vent hose at the bottom and open the gas cap and blow into this hose and check if you hear the sound of air inside the tank.