matas17

depends which gen you are looking at, KWA RM4 ERG has internal spring that can be removed via buffer tube. I don't know about other models so cant comment on that sorry.

the thing is there is not space for spring to push hop unit back towards gearbox so im still trying to figure out the way to keep it in place as the spot where hop unit sits is really open and barrel spring would need to be really long to push against hop unit and outer barrel which attaches to this. Metal spacer/hop unit holder. And also if I can't sort this out what brand mp5 would you recommend me getting instead of this cyma. as I already spent months trying to fix this problem.

Found an issue that had to do with tappet plate as you noted and also hop unit which for some odd reason likes to move back and forth inside receiver like 5cm, No idea why but that seems to cause the issue with the fps drops. Seems like sometimes it goes up to 340fps and then down to 220fps for that reason alone. Gone try and figure out tomorrow which position hop unit has to be in for gun to have decent fps.

- I have tested compression several times with air nozzle on and off and i could not push piston past the cylinder ports - I have checked the air nozzle and it moves easily up and down the cylinder also tried different air nozzle with no issues moving it. - Tappet plate spring is brand new as i bought them to replace original one. - i check FPS with hop off and hop on with same issue, I also replaced Cyma hop unit with G&g mp5 hop unit but had same issue with low fps. - Current hop rubber inside the aeg is Maple leaf decepticon 60 yellow, as i had no issues with them before so i used the same again. - At the moment i have Madbull 6.03 247mm tight bore in it and i tried ZCI 6.02 300mm tight bore and had same issue, and i tied the plumbers tape and it didnt go up in fps

So I had this MP5 for a while now, installed following: Gate Titan SHS 13:1 gears steel tooth piston new piston head 3/4 cylinder double oring cylinder head and 20.4mm oring air nozzle (same length as original one) My issue comes to the point where it fires fire and bbs fly out of a barrel but FPS is extremely low aprox=120-140 with m90 spring and 100% airseal. I am at the point where i cant think of anything else that could cause this. I tried flipping delay chip, trying out different air nozzle, gears, bucking/barrel, etc. I am about to give up on this AEG as i cant figure out what could cause such low fps.

I sorted out the issue but fps keeps jumping from 260-318 on 0.2g bbs but i think thats an issue with hop unit since its cyma because air seal is 100%

Might try different length air nozzles.

Air seal is 100% and I already checked the hop unit and had it fit well all together, I checked air nozzle last bight and it moves back and forth as gun fires. So atm I'm clueless right now.

21.4mm

I bought 21.4mm air nozzle from ak2m4.co.uk and iit had 21.4mm nozzle but still won't fire. It shoots like once in a while. I had bbs roll out of a barrel so I assume nozzle is too short don't think it could be too long.

So i have recently got an mp5 from my mate that he doesnt use. And me being me i installed all upgrades i could get: 14 tooth steel tooth piston/ shs piston head SHS double oring air nozzle 21.4mm double oring cylinder head 3/4 cylinder 13:1 shs gears SHS gear delay chip SHS HT motor Gate Titan But i am stuck right now as the gun doesnt feed at all no matter what i tried. I dont know if its an air nozzle or what but i have tried everything. Any advice would be helpful.