V3 mechbox not firing, what I do to "fix it" ,and what does it mean?

[Troy T. Moore]

Hello all,

I delved in to the world of project guns as I have built an ak104.

I bought a Guarder FTK for the mechbox (CYMA) that I had already. I bought a Prometheus hard cut-off lever. It has a G&P 140 motor and is powered by a 8.4V 3600ma large battery with a Mark III trigger master.

So what happens is that it will fire fine for a while using either the 3 round burst/full auto or semi but then it will not fire. No rhyme nor reason, but usually on the burst/full auto selection. I pull the trigger and nothing. So I pop odd the motor cage, take pressure off the anti-reversal latch and let the spring totally decompress, put it back together and it fires beautifully....for a while.

What I think is that the gears are too fast and the battery motor combo pushes too far, even with the motor braking from the Trigger Master (at least , as I understand, the TM Mark III does provide soft start and motor braking) so that the cam that rubs against the cut-off lever is in the position that results in "cut-off". Am I on the right track here?

The rate of fire is stupid at around 21BB/sec, with 380 fps (I think I have an airleak, but that is another thing that I know how to trouble shoot from the info on ASC and other forums). I am wanting to put in some torque up gears to slow the rate of fire, and also reduce the inertia that is carried in the gears that are geared higher (spinning faster). I know that I can slow the motor down with the TM, but it also means it has less torgue for the M120 spring that is in there...

My son's stock Kalash AK74U infrequently has the same issue and I use the same method to "fix it". It is powered by an 8.4v stick battery...

Any and all help is greatly appreciated.

Thank you.

[Styrak]

Most likely it's the cutoff lever/selector lever spring.

It's either too weak and not pushing with enough force, or it's catching on something.

The cause is usually that the cutoff lever gets stuck in between modes and therefore won't let the gun fire.
Is your trigger also clicking when this happens? That's a sure sign it's what I said, I've seen it happen a few times.

[Troy T. Moore]

@Styrak,

Yes, the trigger "clicks". I am able to pull it back like I would normally. But what I don't understand is that I am not switching between modes at the time. It does not happen when I go from burst/auto to semi or vice versa. It happens when I am using burst/auto between times that I pull the trigger. Working, release, working, release, "click".

[Styrak]

Yep, that's the symptoms I've seen before.