JG M4 S-System not feeding BB's

[ptitza]

Hi, everybody.
Recently i've purchased an used JG M4, in "hopefully working" condition.
First problem - i've managed to find by myself, tapped plate was not attached to the nozzle. Now, i've put everything back, the gun just won't load any BB's.
I've found a thread here in which somebody had worn tappet plate problem, and the nozzle wasnt' moving backwards enough. I'm not sure whether it is the case, when i split the receiver and fire it on semi-auto, 3-4 bb's manage to jump out during single cycle. Also, the barrel is clean, everything looks normal.
When i put single bb directly into the "chamber", it will fire just fine.
Quite honestly i'm out of ideas, except for maybe "lets buy new hop-up, new tappet and hope everything will be fine". Could somebody help?

[ptitza]

Meanwhile, my own investigation went down like this (do not forget that this is my first AEG):

Removed inner barrel with hop-up unit.
Holding it to the nozzle fired a few times - nothing
Moved it a little bit - whoa, bb's started to come out from the correct end of the barrel
Re-attached, verified that inner seats good and tight, reattached upper to lower - still no luck. And then, i've tried to fire without pushing the upper receiver firmly - and the gun started working. So, it seems like either gearbox is not sitting tightly where it should be, or the hop-up unit is too far out (which is weird, since everything looks good there).

[etd]

the wording in your second post is confusing to me so I broke things up as to not waste your time. Is your mechbox cycling on it's own when you pull the trigger? If it is go to solution 2, if not go to solution 1.

solution 1) if your mechbox isn't cycling when you pull the trigger, and the only time it does is when it's attached to the tower receiver it's safe to say that the issue is the power circuit. Something might be arcing or their maybe a loose connectiong with the wiring.

solution 2) I am the guy with that tapplet plate issue btw. It wAnst the tapplet plate Nd I really doubt yours is also. The problem is actually really simple. Either your hopup rubber is torn, installed incorrectly or your mag isn't feeding properly (common with hi caps). You can start diagnosing by figuring out what it isn't. Follow a YouTube vid on how to dissemble the hopup. Than check the hopup rubber for cracks. Make sure nothing is to worn to obstruct the bbs. If this isn't the problem than it has to be your mag. Now I say this because it's extremely rare that tappet plates get so worn like that. 9/10 they break before they cause misfeeding issues. If your gun fires in semi it's most likely not a gearbox issue.

I am speaking from experience here btw. I just fixed this issue with my sig 552. I spent over $200 replacing various parts in an attempt to troubleshoot on my own. The best learning method for airsoft guns is logic. You will learn quickly as long as you keep your cool. This won't be the last time your gun will fail. Just stick with it and you will be able to fix nearly everything. Good luck and merry Christmas.

[ptitza]

Thanks a lot for the reply
It might be feeding problem of the mag - new one is on the way, just in case - i'll need it anyway, but i doubt that.
Well, it looks like this: the gun will only fire if upper receiver is a little bit at the angle relatively to the lower.

This is the gun itselft, it won't shoot this way:


And it will this way:



Note the position of the upper receiver relatively to lower.

[ptitza]

Oh, sorry - and of course, the gun cycles in both situations without any problem
When i've reinstalled the tapped plate, i've also looked at everything, looks fine.

[etd]

Well I know the problem isn't the tappet plate for sure now. the position of the receiver wouldn't effect it at all. It's not the wiring now that we cleared that up. what I would ask you to do is remove the hopup assembly and pay close attention to the angle of the air nozzle without the upper receiver attached. Pull the trigger. While the mechbox is pressed into the lower receiver, and firing, is the airbozzle running parrel and straight back and forth? If it is i'd rule out a mechbox issue forsure. The airbozzle might be hitting the intake of the hopup if it's not running parrelle. So the next step is tonkeep the upper reciever off and adding in the hopup. Now try cycling the gun. DO NOT DO THIS WITH A BB IN THE CHAMBER! You should be able to use semi autobto better see this. if the hopup and barrel are also parrelle and even there should be no issue here. If everything looks fine that leaves the mag. You can Aldo look through the magwell and you should be able to see the airnozzle tip going in and out of there aswell.

[etd]

I apologize for the massive amount of typos. My iPhone isn't cooperating today.

[ptitza]

Ok
Hop-up taken apart and re-assebled carefully
Now it "almost" works - only pull upper receiver a millimeter apart from the lower and it shoots.

[Azathoth]

Which direction are you pulling the upper and lower apart and do you have a 2pc or a 1pc hopup

[ptitza]

I'm pulling it upwards (just like on the photo above, but less is needed now).
Hopup is one-piece

[ptitza]

And finally found a solution.
Got small plastic piece, cut it to cylinder's shape and glued it to cylinder (degreased with vodka, finest russian customs) so it acts like a shim between cylinder and hop-up unit.
Now it works

[ptitza]

Well, I had my hopes to high, i guess.
No, it's not working
On full auto no fire at all, on semi - sometimes fires.
Removed the shim - back to the situation as on photos.
I will also try a little bigger/harder shim, but i think it won't help - i've added two layers of tape just to try it out without any luck.
And no, it's not mag feeding problem unfortunately

[ptitza]

I've noticed one strange thing:
when going over diagram http://www.airsplat.com/Manuals/ERM-M4A1-604-31.jpg
The spring that seats over the inner barrel between the housing and hop-up unit is missing.
It might be the reason of my troubles, actually...