Speedfight 2 bogging down when throttle applied *FIXED*

Just registered here to share my recent findings since many threads when googled are 5 years old and does not contain a solution.
I recently bought a Speedfight 2 50cc with minor issues. Started fine when cold and warm and idled perfectly during both warm and cold. Driving away no problem but after 50 meters when letting of the throttle at an intersection the power was almost gone. Had to "wiggle" the throttle to get the revs up so I could drive away. This problem persisted every time. I replaced the fuel and took out carb to clean it (was fine, no crud but some slime) and when put back same thing, did not get any better. To make a long story short - I decided that it HAD to be fuelrelated. I took off the left sidecover to inspect the seethrough filter while revving up. I noticed that it quickly drained to about 10-15% of the volume in there but fuel was dripping in so I knew vaccumthingy was working atleast. It was ok when revving up while standing still but had some minor thoughts about loosing power for a few seconds and that persisted, the fuel filter was still letting fuel through. Took it for a run around the house and same thing again.

Now to the "fixed"-part. I replaced the filter with a new one (I blew through the filter and it was fine - or so I thought) also see through and after a few seconds it filled up and THEN when revving it up it did not emtpy to 10 -15% as the first filter did that looked fine when inspected ocular. Then started the testrun and it was 100% fixed no more thinking about giving power after a short while but just giving it the full beans every time revving up. The bogging was/is gone!
And the answer why is simple, filter although looking fine/blowing through can be deceiving because the paper-part in the filter looses its ability to let gasoline through in the manner it is suppose to flow trough (remember the slime I mentioned?)
So I really hope that this helps another fellow guy to sort out the problem they are having. I used one of my 10-pack ebay smallenginge-filter for 2.50€ to sort this out. It does not matter what kind of filter you use it will still gunk up when scooter is not being used.
/Sincerely Yours
Marc from Finland

 

This.
This is gold.
As a mechanic I've lost count of how often a bad running issue isn't a coil, or cylinder or whatever, but a bit of dirt, or a shitty plug.
Change the cheap parts first.
Then test the more expensive stuff.
People forget fuel filters are a service item.