CYMA P90 Mis-feeding

[MrTea]

Bought from another user on here who says it was only firing a BB every 2nd shot.

I've re-shimmed, re-greased, replaced tappet plate, new hop rubber and nub. I've now got the RIF firing at the proper speed it should be for 13:1 gears, I believe the motor was adjusted too high, binding the gearbox causing it to fire sluggishly. Currently it has SHS nozzle, SHS piston, SHS 13:1 gears and Rocket high torque motor.

The gear set already has a sector delayer on there and it has a new tappet plate so i'm not sure what else to do on the RIF itself. In my testing I found that it appeared to be feeding fine in semi but as I got through the magazine, it began to mis-feed. In full auto, even with a full mag, it struggles to feed.

Do I need to buy some stronger springs for the mid-cap magazines so they can keep up with the RIF? I know I can get Maple Airsoft super feed springs but I don't want to throw £15 on three springs if the mags aren't the issue. I will note however that when I emptied the magazines, the BBs didn't race out like they usually do on my other mid-caps, it was noticeably slow.

If the gun is simply too fast, I have some 14:1 gears I can try out next to see if it slows it enough to allow feeding.

Ty.

 

[Pseudotectonic]

sounds like it's the magazine

have you tried opening up the magazine and clean it

 

[MrTea]

sounds like it's the magazine

have you tried opening up the magazine and clean it

I used the CYMA mags it came with and some brand new King Arms ones. Mis-feeds on both.

 

[Pseudotectonic]

new tappet plate - is it sliding without friction?

sometimes new tappet plates don't slide well, might be too thick etc

 

[MrTea]

new tappet plate - is it sliding without friction?

sometimes new tappet plates don't slide well, might be too thick etc

It appeared to be when I was testing it. I have a CYMA replacement (current one is Guarder) coming in so I might swap it with that and see what, if any, difference it makes.

 

[MrTea]

new tappet plate - is it sliding without friction?

sometimes new tappet plates don't slide well, might be too thick etc

As an interesting bit of info. I was picking peoples brains in different places and someone suggested just trying different hop rubbers before you rip open the gearbox again. I went back and grabbed the standard hop rubber and a prommy purple in addition to the ML Macaron already in place.

View attachment 119218

View attachment 119219

It looks like with the ML Macaron, the feed lips are a tad too long and are protruding into the feed 'channel' enough to cause feeding issues. The first pic is basically how both the stock rubber and prommy purple rubber look, they're almost impossible to see as the lips are a tad shorter than the ML ones.

I tested it by firing half a mag in semi auto (which worked fine) and then half a mag in full auto. The full auto struggled to keep up just because the gun is cycling that fast but never stopped feeding where I had to fire in semi or a small burst to get it to feed again. I could probably remedy this by using a .1mm or .2mm shorter nozzle while not preventing a proper airseal from being formed. Something to test going forward. Just got to get this into a skirmish and see how it performs.

It's annoying I ran into this issue again and didn't think about it sooner. Had literally this exact thing happen when building my DMR.

 

[The_Lord_Poncho]

A common issue with the Macaron rubbers I hear. I've certainly experienced it too. I can't say for certain, but i believe that the later 'super macaron' rubbers - the ones with the wavy lines/ribs around the outside rather than the earlier straight ribs - do not suffer from the same problem. Unfortunately they are somewhat harder to find for a good price, I'm reckoning that retailers bought up a large stock of the earlier rubbers and are still drawing down on that stock before they re-stock with the super macaron.

 

[MrTea]

A common issue with the Macaron rubbers I hear. I've certainly experienced it too. I can't say for certain, but i believe that the later 'super macaron' rubbers - the ones with the wavy lines/ribs around the outside rather than the earlier straight ribs - do not suffer from the same problem. Unfortunately they are somewhat harder to find for a good price, I'm reckoning that retailers bought up a large stock of the earlier rubbers and are still drawing down on that stock before they re-stock with the super macaron.

Only ever had it happen to me on the A&K Masada DMR that I've been building. A&K being a Chinese company appear to use different specs where ML rubbers don't work well. It never caused feeding issues just wildly inconsistent FPS; about 50-60fps difference across 10-20 shots.

After all that of me acting like a smart-ass thinking i'd fixed it, the issue returned when I went to show it off. I grabbed my other P90 that's in a storage bag (which just so happens to be stock) and watched the nozzle as I fired it. That nozzle never stopped in the feed tube/port/window once in semi-auto where the CYMA P90 would regularly be visible, as can be seen in previous pics. Knowing that it's an SHS part the previous owner has installed, I had ordered a 20.75mm and 20.7mm nozzle so I tried that next and went straight to the 20.7mm nozzle knowing the SHS nozzle was 20.8mm.

Took a full mag and fired it in full auto with no miss feeding. I'm hoping, praying, that I might have gotten to the bottom of it. Across 15 shots in semi the FPS is consistent at just over 300fps on 0.2g BBs with less than 4fps difference between highest and lowest reading which is surprising because the compression parts feel pretty poor and it's still using a plastic piston rack. I'll have a dig around for an M100 spring to get it closer to the limit and i'll re-try using the ML Macaron rubber to see if it still causes the feed issue.