New problem on M4

[ar15]

Hey guys, I ran into an issue on you of the kids guns this weekend that I have never seen before. First the gun is an Echo 1 M4 and has the stock echo 1 motor. It's running an M120 spring, shs blue piston, stock piston and cylinder heads and cylinder. The nozzle was changed about 2 months ago with the other upgraded parts. The gun has worked great for over two months. On Friday, the gun starting shooting much lower fps on semi and would occasionally spit out 2-4 BBs in a group. The gun seems to work without issues on full auto.

I thought it could be the hop up bucking or sealing issue. I broke down the gun and cleaned the barrel. I also replaced the bucking with a brand new one, and the nub too. I cleaned up the entire hop up unit too. Lastly, I sealed the whole unit with Teflon tape. Same issue on semi auto, no change whatsoever. So clearly the problem must be inside the gearbox or some other area of poor compression. Why would it work on full auto and not on semi???

I am sure you guys have heard this issue before. I am a new parent to airsoft but the engineer in me has really enjoyed modding and repairing these things. I look forward to some ideas to target so I don't just tear the gearbox open with a shotgun approach to the repair.

Thanks,
Dave M.

[T6e9a]

A sector clip may help with cycling the tappet plate. Make sure your tappet plate is in good condition, check to make sure there are no chips in the air nozzle, or where the tappet plate holds the air nozzle.

That's what I would think to check.

Also, make sure the hop up is pressed up against the gearbox. Either with a spring, or I prefer o-rings as they provide a more consistent pressure.

[ar15]

How do you use o-rings to make sure the hop up is tight against the nozzle??

Dave

[T6e9a]

I don't quite remember what size, but you just slide them down the barrel until they are up against the hop up. They provide a stuff spacer between the outer barrel and the hop up unit, and press it firmly against the gearbox. I'll update this post with a picture in a little.



Sometimes 1 is all you need, sometimes you need more. But it is much more consistent of pressure as opposed to the spring that is usually doing the same job.

[ar15]

That looks awesome. I am upgrading a new G&G CM16 Mod 0 and I plan to use this tip.

Thanks Tech9

Dave

[T6e9a]

Did you figure out the issues with the gun mentioned in the original post?

And glad to help.

[ar15]

Not yet but I am planning to come into the store today. Should I bring it?

[T6e9a]

Yeah, should be able to help you out.