Getting frusterated....need a troubleshoot

[Buds and Suds]

For starters, big time new at this....I just got my first AEG, a CA M15A4 SPC
I upgraded.....first time doing it and followed mechbox.com instructions.
From stock I added:

m120 spring
tightbore barrel
new tappet plate (with this gun I heard stock one imminantly breaks)
Gun came stock with metal bushings.

Bought a polycarb piston but did not install it yet, going to wait for a new piston head as well. Read that this gun with the spring I have did not need new piston off the bat so im waiting.

Symptoms:
substantial power loss, at 2 inches does not penetrate a soda can, just dents it.
After 4th reasembly the bbs are not feeding properly, one comes out approx every 3 pulls of the trigger.

Things ive checked:
After 4 times in my mechbox, each time I could find nothing wrong with the assembly. Timing is correct, cylinder hole is towards the rear, spring is inserted correctly, greased and siliconed. Never had a problem with the gun acctually firing and have found no wear on anything internaly.
I also checked my hopup sleave and barrel and siliconed the barrel. Only thing I noted is that when I drop a bb down the barrel it will stick in the hopup sleave, but the slightest push with send it through (not sure if this is normal?)

Anyways, I am at a loss and need some help. Only thing I can think of is an airleak but I checked my seals and it looks the same....brand new!
I did fire 600 rounds with no problem before I took it apart, so it was a working gun before hand. Thanks

[CDN_Stalker]

Pretty observant new guy if you ask me!

Not sure what the prob is yet, will ponder for a while. To answer your question, yes it's normal for the BB to be held in place by the hop up rubber in the barrel.

Is it safe to assume you have the tappet and nozzle hooked up correctly?

[TokyoSeven]

I would just like to inquire about the type of battery you are using.
I know its only a small possibility but perhaps you do not have enough power to crank that spring. If I can think of anything else I'll let you know.

[Buds and Suds]

Originally Posted by CDN_Stalker

Is it safe to assume you have the tappet and nozzle hooked up correctly?

As far as I could tell there is really only way to assemle the nozzle and tappet plate. I looked in detail at a still pic of the mechbox.com video to compare and I couldnt see a difference. Now the hole in the cylinder...does the orientation matter, the rotation? I know it has to be towards the rear but if I was to point it straight up I can cover the hole.

My battery is a 8.4v 3000 mah. I talked to a guy who owns this exact gun and spring setup and he has a 8.4v 3600mah and its going ok for him.

I guess ill take my gun apart again and give er another look, but I dont think im going to find anything new. Any pointers would be great cause im missing my first game today because of this.not a happy capper.

[Syn]

That " tightbore barrel" you put in is it longer than stock? Because if it is longer you could be having bb suck back which would explain the loss of FPS.

[Buds and Suds]

Originally Posted by Syn

That " tightbore barrel" you put in is it longer than stock? Because if it is longer you could be having bb suck back which would explain the loss of FPS.

No, its the same, I even put the old barrel back in and tested it, same deal. so I think its safe to say its not the barrel, which leaves the hop-up ( dont think its that ) or somthing internally. Im kind of tempted to put the old spring back in and see if that clears fixes anything. But far as I know a 8.4 should be able to drive a M120.

[Syn]

Yep if it is not obvious, I would put the old spring back to isolate the part that is not fuctioning properly. Also your shimming is good right?

[Dynamo]

take the gun apart so you can access loading nozzle.
plug in you batt and fire.
does the nozzle move back then forward with every shot?
if it does, place a finger over the nozzle, and press just firmly enough to make an airtight seal.
fire and see it there is good compression in the cylender.

[TokyoSeven]

If youve got the time, I say put it all back together with stock and see if it works like that, unfortunetly you may have had a certain part fail somewhere along the ways. But well no harm no foul, might as well put it together stock and see she goes.

You are correct about the battery though, that batt should pump that spring fine.

[Buds and Suds]

Originally Posted by Dynamo

take the gun apart so you can access loading nozzle.
plug in you batt and fire.
does the nozzle move back then forward with every shot?
if it does, place a finger over the nozzle, and press just firmly enough to make an airtight seal.
fire and see it there is good compression in the cylender.

I tried this, it moves back then forth, I put my finger over it but dont know how to tell if it has good compression. what am I looking for? im not feeling much air on my finger covering the nozzle. but when I take my finger off I can feel the air about 2 feet away on the palm of my hand. 3feet away I cant feel it. I can also feel air pushing out of the cylinder hole, bit not from any seams nor the rear hole that exposes the spring.

[ILLusion]

Compression test:

Open up the gearbox, removing the spring guide and spring.

Cover the air nozzle with your right index finger.

Using your left hand, draw the piston back and with a good amount of force, slam the piston forward. If you have a good seal, you should actually be able to get the piston to come to a complete stop, held back only by pneumatic pressure. The more forceful your push, the more likely you should come to a complete stop. If you feel air releasing on to your right hand anywhere, you'll need to localize it.

[Buds and Suds]

So far........ took it apart....again... and dropped in the stock spring, no change.
Did the compression test and with the plastic nozzle piece taken off, putting my finger over the metal spout on the cylinder head (not the plastic nozzle) made the piston stop immediatly, even without having to slam it (Piston and cylinder head ruled out). With the plastic nozzle on, I could not bring my piston to a stop no matter how hard I tried. There was some resistance but I could not make it stop and could hear air escaping from the base of it. But since there is nothing to seal it, this must be normal. So I put the M120 spring back in, fired it again, and got 1 shot out of 5 to go through the side of the can at 1-2 inches. ugh.. stress.

Also, the last 2-3 bbs in my mag never load, they just fall out when I release the mag. Any ideas? im thinking of replacing the nozzle and maybe get a new piston head and cylinder head. Just to get everything covered, but dont really want to spend much more $$$

[ex]

Originally Posted by Buds and Suds

Also, the last 2-3 bbs in my mag never load, they just fall out when I release the mag. Any ideas?

This is normal...no worries.

[Nova316]

2-3 bb's fall out of your mag is normal happens to me to its cause it loads 4 into your hopup chamber, the only time this doesnt happen is when my mags has a piece that protudes the top when empty.

Check your hopup rubber as well its on your barrel in the hopup for any cracks or breaks, that can reduce FPS if its not a tight enough seal or if its bent and getting in the way of the bb

[Buds and Suds]

Ugh, ok so my rifle is now firing 250-280ish according to my soda can crono, regardless of me using the stock or upgraded m120 spring. It fires at the same FPS it seems, and yes the 2 springs are obviously different in stiffness. ive taken the mechbox apart 6 times now looking for faults....nothing. Im getting good compression between the Piston head and cylinder head, not including the plastic nozzle. It fires straight at 20 ft ( its all the space I have for testing). Problem with all of this is I have no other mechbox to compare this all to. This point im almost ready to replace Piston and head, Cylinder head, nozzle, hopup rubber. Even though I dont see anything wrong with these parts, I dont know what else to do here, and Id hate to install it all to find out its not the issue. Far as I know this 120 spring should be shredding cans at 25-30ft, and well.....its not even close. Thanks for all the help so far, ive looked into every suggestion, but so far nothing. Im sure someone who has done this alot would take a 1/2 hour and go......"oh here, this is the problem", but I dont have the luxury of knowing anyone locally here who knows this stuff. Thanks again, and ill still take suggestions.