King Arms m4 AEG firing full auto in semi mode

[Scrivah]

Hey guys, did a search and couldn't find what I was looking for.

Here is my issue:

King Arms M4 AEG fully stock at the moment.

When i put the selector on Semi-Auto and pull the trigger fast all the way back it fires 1 rounds as designed. But when I pull the trigger slowly it starts firing full auto until the trigger is fully pulled back (up to 10 rounds at times).

I play with a group that usually plays semi-auto only so you can see my issue!

Some reading on google says it may be the 'cut off lever' and it may need to be modified. Others say the 'trolley'. I would rather just upgrade a part/parts if needed as I am all for making my gun better, but dont want to just start buying parts blindly.

If anyone knows or has had this issue in the past I would love to hear your thoughts on a fix! I know that this seems to be a common problem with the King Arms M4.

Thanks!

[Stealth]

It's your electrical contacts.
The trigger "sled" is making electrical contact with the wings and causing your gun to fire before it has slid back far enough for the cut-off lever to disengage it.

Just modify the wings a bit so that they will close up later in the sled's travel. Make sure you test it out with a multimeter before closing it up. Opening it up too much can make your gun inoperable.

[lurkingknight]

the prongs on the trigger switch side are probably a little too close together so the trolley gets stuck until the cutoff hits it enough times to loosen it out. Sadly, you need to take the gearbox apart to get at it enough that you can see and adjust it.

The other cause is indeed a worn cutoff lever. If it's a newer gun chances are you won't have to replace anything but the cutoff lever is a wear part, and it's nice to have one standing by to go in if you need to change it.

For the trigger, you don't need to buy a new part, just bend the prongs a tiny bit farther apart so the trolley still slides the block in, but it doesn't get stuck.

[Scrivah]

Thanks guys I will give this a whirl. I am a noob on the dissassembly but I hav watched a few vids on the v2 mechbox so I am confident I can get in ok. (i just have to watch out for the flying spring when i take the two halves apart!). Haha

[lurkingknight]

release the anti reverse lever before you split the gearbox.


Split the halves in a pillow case till you get used to doing it/and or know where all the parts are supposed to go if you blow it up.

[Scrivah]

So just so I get this right you guys both seem to agree its the same thing? Stealth says wings, lurkingknight says prongs but essentially you are saying the same thing right?

I have never taken apart the mechbox before so just to help out a bit more could you explain size, colour, location? And how far apart should i move the wings/prongs? (half mm, full mm?)

Thanks guys

[THe_Silencer]

GDS-4005 Airsoft AEG MOSFET testing in King Arms gearbox - YouTube This vid should clear it up since it's an actual KA mechbox. knight and Stealth are referring to the same thing. The metal contacts on the right side is what you want to pry further apart.

[Scrivah]

That was great thanks for the link to the vid. I can see the two metal pieces that come into contact with each other. Any word on how far I should pry these little tabs apart?

Thanks again

[Stealth]

Originally Posted by THe_Silencer

GDS-4005 Airsoft AEG MOSFET testing in King Arms gearbox - YouTube This vid should clear it up since it's an actual KA mechbox. knight and Stealth are referring to the same thing. The metal contacts on the right side is what you want to pry further apart.

rapturoussex...

[lurkingknight]

it doesn't take much... it's a bit of trial and error. Too little and you get the same issue.. too much and you don't close the circuit and cause the gun to fire.

Go a little bit at a time... it's very little.. we're talking fractions of 1 mm here.


Be super careful when taking the gears out, make sure you keep track of the shims on the gear axles and make sure they stay where they're supposed to go. Unless you feel like reshimming them... which is never a bad idea since it's all open anyways. Look up shimming from the bevel technique.

You can test the tightness of the shuttle by using a screw driver to emulate what the cutoff lever does. If it takes almost no effort to flip the shuttle up and free of the prongs, you're on the right track. You want it be loose enough that the cutoff requires little force to trip it, but tight enough that it all connects to complete the circuit.

[Scrivah]

Great info thanks!

[Scrivah]

Just an Update:

Problem solved! My friend is somewhat of a KA m4 expert and he knew what the problem was right away. All we did was replace the cut off lever with a Tokyo Murai lever and problem solved. I can pull the trigge as slow as possibly and only 1 shot is fired.

Fixed!

[andrewromanchik]

I work on king arms M4s all week long at work and the cut off lever seems to be worn on about 15-20% of the new guns, bit of a problem for them, the trigger tabs are usually a bit tight as well but will typically just cause them to wear down quicker. I really hope king arms fixes this, its one of our best selling guns and I'm sick of swapping cut off levers.

[blanc_bec74]

Bought a KA M8 (Oberland) model and had the same issue. Sent back to TA and they replaced the lower reciever. But played a few weeks ago and the same thing happened. So replace with a new cutoff lever it is....

Thanks all!

[Scrivah]

Originally Posted by blanc_bec74

Bought a KA M8 (Oberland) model and had the same issue. Sent back to TA and they replaced the lower reciever. But played a few weeks ago and the same thing happened. So replace with a new cutoff lever it is....

Thanks all!

Common problem with these guns outta the factory. I hear about 20% suffering from this defect. The next cut-off lever you put in may look the exact same but fix the issue. Myself I put in a TM lever, its just a little bit beefier.