That is a really weird issue.
My first suggestion would be reseating the gearbox maybe? Maybe the selector plate has come loose, and it’s not letting you click all the way over to auto?
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Yep send it back to the retailer 
I don’t know the specifics of your GBX never seen or use one put pics up.
If it’s anything V2 style there are a few things that need to be in the right spot, springs, levers and elec contact.
But you say nothing mechanical so look how the selector lever makes the switch from semi to auto and go from there I guess 
gl
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Where’d you buy it…?..thinking of getting one, but not sure now.
If I sent it back it’ll at least a couple of weeks till I get it back , and I’ve already pulled the g , box out . in semi . It’ll double tap , and auto , I can live with that , I wil probably have to pull the G, box a part eventually, I should have taken a photo when the box was out . Their are two electrical contacts that slide between semi, and auto , I’ll work it out , + a little u tube searching.
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Hi , it’s worth it , full metal it’s all they said it was .
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I have one of these too. So far very happy with the rate of fire on full auto and it feels nice and solid and no weird noises etc. however I am also having issues with semi sometimes firing multiple shots or just working in full auto. I’m running it on 11.1v at the moment and thought it may be running on due to the higher speed and have wondered if it would still happen on 7.4v but haven’t got around to testing this yet. My other issue with it is how much it ready sprays the gels everywhere. Not trying to suggest a gel blaster should be that accurate but compared to my wells m4, this thing is terribly ‘inaccurate’. However definitely still good for spray and pray, so I figure just bring plenty of mags 
. If you pull it apart again it would be great if you could post some photo’s and info. This can be so helpful for others looking to pull it apart for the first time etc. Also we have some very knowledgeable people on this forum that I’m sure could identify what it’s running internally and things to try to fix the problem. If I get around to testing it on 7.4v or actually pull it apart I’ll post an update with the details.
Hi , I use a hopup, rizer , it shoot 30mts straight, the auto bugs me , no semi , have all ready pulled apart , ,it’s a v2. Gear box but , the. Trigger switch, has elec contacts which controls semi , and auto, have been over utube researching, air soft has problem s as well , if only I could purchase the right parts. Would help , you might be right. About 7.4 volt , I might give it a try as well, my GBX only worked once in semi , with the 11 volt, thenAUTO ONLY
I have absolutely no experience with any of these GBX blasters, but plenty of experience with everything else
Photos help when people are asking questions about faulty blasters.
There’s got to be a simple process to follow which works through the testing of the basic functions first before delving into more technical details.
By checking that all the basics are functioning correctly, only then can the actual issue be found through more thorough investigation.
Following this stream of thought….
Single/Full Auto is either mechanical or electrical.
You are saying V2 mechanical switch, which isolates the issue down to two simple functioning parts.
The selector plate/contacts/switch and the physical trigger switch in the gearbox.
(See below)
Both must be thoroughly tested for correct travel and engagement…… which is the only two details that will make it operate as designed.
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Am I correct that these run the external sliding switch plate on the LHS of the gearbox and not a MOSFET style trigger?
Other gearboxes have the tiny rocker arm that runs off a small cam on your sector gear to engage/disengage semi/automatic…., which would obviously be called a mechanical selector, not electrical.
Has the gearbox been taken apart and this part not installed correctly, or just possibly fallen out of place and caused this issue 
Hi , it does have a rocker arm, and sliding selector plate and two electrical connectors and a small cam on the sector gear., I’ve taken apart twice to check rocker arm , ext, I’ve nothing to compare, if it was mechanical it’s easy , or I could swap over for a mechanical v2 switch , if I could purchase the right parts I could probably sort it out, I’ve plenty of v2 bits .
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If it’s V2 anything for V2 will fit. Check your cut off lever under the sector gear and the cut off lever spring on the slide plate.
Does it even look like this in the video? This is a mechanical switch.
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Hi, well ,well ,well, popped in 7.4 battery , semi, ok auto ok, , slow rate of fire , I noticed the cam lobe is very small on the sector gear , could I up grade the gears to, ummmm maybe 16 to 1 , or 13 to 1 , to increase ROF , , yep I check the video out, same in side ., may be much voltage , causing auto fire only, do you think up grading gears and keeping 7.4 v, would increase ROF . Cheers Clyde .
It likely would have the same result as will spin the lobe faster as well. But a set of quality gears may help solve the problem if the lobe is not to standard on your current gears, guessing they are cast.
You could also look at replacing the springs on the trolley and the cut off lever for stiffer ones might help.
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Mmmm good to hear the result of using 7.4v fixing semi, but then you lose the higher rate of fire. I love the 11.1v rate of fire .
Hi , new shs gears coming and hardened springs even a shs cutoff lever.
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Yep , charging gears , good ones, ext, ext cut off lever and better springs. To see weather better quality sorts it out .
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Hi, up date , did some research over xmas via utube, have now discovered that the cut off lever is cheap alloy, and has broken off the tip end that allows semi auto, , I’ve purchased SHS cut off level, also discovered that the plunger has no metal rack, I’ll fix that as well . Cheers Clyde .
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Would you still recommend the GBX…??
Tempted to buy one at $220 as it has metal gears etc, but I don’t want to have to mod it or pull it apart.
I want to run an 11v battery and have it last.
Would it be better (for me) to spend more and get something that doesn’t have any inherent problems…??
Thx
Hi , I could have sent it back , would’ve been a few weeks turnaround post, it was a easy fix , other wise $220 is cheap , with a hop up it’s good no other complaints .
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Great stuff, was thinking must be something to do with the cut off lever or maybe the springs that run it can give trouble on higher voltage.
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