Bit confused here....
It "sounds" like a possible COL but gun is new-ish or recently purchased
(but then 2 round burst on auto sounds odd)
Ahhh but it is an ETU fuck pig so that would explain a burst on auto
(but that would be 3rnd or potential 5rnd burst option on ETU2 units)
Now we know the common AK selector issue going from semi/auto/semi etc...
But this TWO round burst is a bit odd - should be 3 (and/or 5 round burst) on ETU I would have thought
but still get single shot semi & then 3 (or 5 option on blue etu2) or just auto on ergh auto
First of all - what battery are you using
ETU's can/do play up on 7.4v so best to run on 9.6v or 11.1v, (11.1v is best perhaps)
(normally, iffy etu's simply refuse to work on lower 7.4v, but wondering if lower volts causing an issue)
Secondly - RTFM (Read The Fucking Manual) for info about setting/changing the burst mode
COULD be an iffy ETU - the main unit near battery, as they are made from Dairy Lea
Turn off/disable the burst mode (RTFM) and start again so semi & auto operates correctly
In that sort of gun, I would have just used 11.1v with 18k motor to get you near say 20rps
and with the 22k you should be on or just a whisker over 20rps
It appears to be crane stock AK so assume the battery goes under the hood/dust cover
which this battery MIGHT be about your limit - but YOU need to check it will fit (inc wires)
https://hobbyking.com/en_us/turnigy-nano-tech-1300mah-3s-25-50c-lipo-airsoft-pack.html?queryID=c2ca5915ed20ee36fc43e6fc49de517d&objectID=31045&indexName=hbk_live_magento_en_us_products
RTFM, check your battery is OK, and give us a bit more info...
it might be a moody selector, but the etu causes more issues in some guns than it is supposed to solve
or if gun is still in warranty contact retailer (hmm good luck with that)
but I'm a little confused with 2rnd burst in both modes so if possible read manual, turn off burst etc...
and update us with a bit more info perhaps