M4A1 GEN9 - firing and trigger issues

Hey guys could really use some advice. I took apart my M4 and put in a 1.3 spring, o-ring and upgraded the battery. The rest is stock.

Semi auto function only fires half of the time and then the other times the trigger won’t fully compress so then it won’t fire? Full auto mode works fine.

Also, after firing; an extra gel ball will shoot out but not properly come out, almost like it’s been thrown by an elderly man on his death bed?

Thanks everyone

Ahahaha, love the description, mate.

I’d say the 11.1v battery is spinning the motor in the mag (feeding the gels) faster than when using the 7.4v which is causing more than one gel to be fed into the chamber…

Check out this post (with pics) regarding that:

For the semi-auto function issue, I had that when my motor didn’t have enough juice to finish the task…

When using semi-auto, there is a plastic piece that is tripped by the sector gear which cuts off the trigger contacts thus stopping the motor…
If the spring is too much for the motor/battery, it might stop too early leaving the cut off clip in the way of the trigger (locking it in place) or leaving the spring fully compressed giving the motor a hard time starting up again…

Something to be mindful of, not all 11.1v batteries are equal in the sight of the gel gods… Some provide more juice than others and will perform better when the motor is under stress (the stock motors are pretty average tbh)


I also noticed that my JM G9 did that weird thing with semi auto - For me it was the motor height wasn’t quite set right or I didn’t do a complete trigger pull and the motor had stopped halfway through a cycle.

Full auto also worked fine

(it was completely stock though)


Quality control at its finest :laughing:
Didn’t even think of the pinion gear, definitely something to be mindful of…

Nah that was a Marty control problem. Worked fine until I pulled it apart haha

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Thanks Xtop for the info.

I think you’re right Arty. It sounds and feel like it’s not doing a full rotation so I’ve messed something up or the motor isn’t strong enough. Just was playing with it and it stopped firing and I could hear the gears grinding. Probably shredded the teeth off the gears. Gonna open her up now :upside_down_face:

Okay so the plunger pushes in (towards the barrel tip) but doesn’t return? When the case is open all the gears make contact

So it’s compressing into the cylinder but not being pulled back out again?

Try opening it up again and manually cycling the gears by hand to see where the sector gear teeth meet with the plunger ladder when it’s resting in the cylinder (pics to be safe? Would be easier for us to help :wink:)

Also, try taking out the spring with the case screwed shut and manually cycle the gears with your finger or a screwdriver or something to see if the sector gear will reach the plunger ladder and start pulling it back (when the case isn’t closed, the gears and ladder aren’t held in their proper places and slightly move around skewing the results a bit)

It was the fucking motor hight! Not enough compression so the gears were spinning free. I’m such a noob. Still makes an angry ‘crunch’ noise here and there. I’ve ordered metal gears so hopefully that fixes that

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If the teeth aren’t damaged beyond practical use and you’ve already shimmed the gears as well as you can, you should be able to adjust the big plastic flathead screw behind the motor (bottom of the handle) to push and pull the pinion gear towards or away from the bevel gear…

Metal gears will just make the crunch louder if you don’t get the positioning right (they’re louder in general already)

Edit: Btw, metal gears would be good for 1.3 spring anyway (I’ve seen a video on YouTube of a guy with a 1.3 spring stripping his gears mid-game cause he didn’t bother changing them)

Yeah that’s what I’ve done man. I’m going to look for some vids so I can see what a healthy blaster sounds like. I think I’m in the sweet spot. Haven’t put it together to see if semi auto works but I’ll keep you posted

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Check out Low Guido’s Chop Shop (he says he’s the 2nd best channel on YouTube but he’s totally the best around when it comes to variety of content and thoroughness in testing/information :stuck_out_tongue:)


You can also make a 1S (3.7v battery) and plug that in. Just have the gears in shimmed, no plunger or spring, the 2 halves of the box screwed together… just run the gears and make sure they are not slopping side to side or making noise…

If you test with 11.1v… any issues can break stuff in the blink of an eye…

Once I finish putting it all together, I give it a hit first with a 7.4v to confirm all is well before sticking an 11.1v in there (just in case)

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i have the same issue and im using the standard battery, semi auto fires onces and the trigger gets stuck and doesn’t spring forward, full auto works perfectly fine.

That sounds like the gears are a bit shredded. I’d check the motor hight (might not be in far enough) and also open up the gearbox to check for foreign objects, plastic, teeth off your gears…

U still experiencing issues with this mate? Mine does some burst fire on semi and then the trigger will get stuck occasionally. Full auto works fine.

The thing is, I did actually test the gearbox out of the receiver. The semi shot works fine. It was when I assembled it into the receiver that I got semi shot issues.

I am starting to think that the fire selector did not engage the fire selector plate properly on semi. Does anyone else experience this?