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Hop Up Problems


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#1 brooklyn468

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Posted 31 August 2008 - 04:01 PM

My KWA KM-4a1 is officially 6k bbs old. Today I was at my field at our monthly outing, and my gun crono'd at 300 fps. Immediatly I knew something was wrong. But, as long as it was shooting, and because I had no time to fix it, I put in a clip and headed into the first field.

I briefly tried to adjust my hop up and it didn't do anything. Just to be safe, I put it down all the way, and I played our first 2 rounds of the day.

After those rounds, I went to crono my gun again, and it shot around 320 every time. Better, but still not what it should be at. I also found out my hop up was not doing anything.

So I played the rest of the day with a rifle that had no working no hop up.

I also know that it was NOT the chrono, a buddy of mine had the exact same rifle as mine, 16k bbs or so old, and it shot at 400 or so consistantly.

I was asking some of the guys there, and they said I needed a new " hop up spacer " , or a complete new hop up system.

Here are the specs:
With .2 Airsoft Elite, 290- 330 fps

With .25 bbs ( I forgot the brand, but it was high polished ) around 280 fps

With .12 ( Just for kicks, I am aware of the dangers ) around 400 fps

I recently rewired to the back for a crane stock, I am using an 8.4v 4200 mah battery.

Could you help me out? Thanks guys. :)

I will try cleaning my bucking and see where I am at from there.

#2 Shmoogly3

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Posted 31 August 2008 - 05:13 PM

First clean your barrel Your hop up chamber could be cracked somewhere and some of the pressure is being lost. I really don't think your hop up nub has anything to do with your fps drop. Another thing that could have happened is your piston cracked.

Edited by Shmoogly3, 31 August 2008 - 05:14 PM.


#3 brooklyn468

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Posted 31 August 2008 - 05:42 PM

View PostShmoogly3, on Aug 31 2008, 08:13 PM, said:

First clean your barrel Your hop up chamber could be cracked somewhere and some of the pressure is being lost. I really don't think your hop up nub has anything to do with your fps drop. Another thing that could have happened is your piston cracked.

Alright I'll do that and check my piston. Then I'll say what happened.

I'll also clean my bucking.

Thanks  :)

#4 vic_man4

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Posted 31 August 2008 - 06:29 PM

View PostShmoogly3, on Aug 31 2008, 05:13 PM, said:

First clean your barrel Your hop up chamber could be cracked somewhere and some of the pressure is being lost. I really don't think your hop up nub has anything to do with your fps drop. Another thing that could have happened is your piston cracked.

I was thinking the same, could also be a shot O-ring or cracked air-nozzle. Just take a close examination at your hopup chamber incase its cracked, if not then proceed to taking your gearbox apart for further examination of the problem ;)

#5 brooklyn468

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Posted 31 August 2008 - 06:52 PM

View Postvic_man4, on Aug 31 2008, 09:29 PM, said:

I was thinking the same, could also be a shot O-ring or cracked air-nozzle. Just take a close examination at your hopup chamber incase its cracked, if not then proceed to taking your gearbox apart for further examination of the problem ;)

I have sucessfully fixed my hop up. I had to take it apart and the spacer ( or at least I think it is called the spacer ) was out of place.

I will take an examination of the gearbox next.

Thanks for your help, I'll get back to you for results.

And does anyone have a link to a poor man's crono? I don't have an official one with me  :lol:

#6 vic_man4

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Posted 31 August 2008 - 06:59 PM

View Postbrooklyn468, on Aug 31 2008, 07:52 PM, said:

I have sucessfully fixed my hop up. I had to take it apart and the spacer ( or at least I think it is called the spacer ) was out of place.

I will take an examination of the gearbox next.

Thanks for your help, I'll get back to you for results.

And does anyone have a link to a poor man's crono? I don't have an official one with me  :lol:

Im pretty sure if it can go through the bottom of the can then its 400fps. Something like that :lol:

#7 Shmoogly3

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Posted 31 August 2008 - 08:45 PM

One Side…………….290+FPS
Both Sides…………..340+FPS
Bottom Center………385+FPS*
Bottom Edge………...450+FPS
Top Center…………..470+FPS
Top Edge……………500+FPS

#8 karMeister

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Posted 01 September 2008 - 05:51 AM

After 80k+ rounds I switched to an SP130, 6.02  395mm Tighbore, Guarder Bearing Spring Guide and Guarder Bearings (I didn't change the piston head just the bearings I had from a guarder piston head.)

I reached a steady average of 453 fps on .25 (ICS Prof. BBs)
Before the tournament we had yesterday, after 3 bags of BBs,  it chronoed 431 on .25s
I used a bag and a half on that tournament. ( 7K+)

Note that I havn't changed the Piston Body yet.

#9 brooklyn468

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Posted 01 September 2008 - 08:46 AM

View PostShmoogly3, on Aug 31 2008, 11:45 PM, said:

One Side…………….290+FPS
Both Sides…………..340+FPS
Bottom Center………385+FPS*
Bottom Edge………...450+FPS
Top Center…………..470+FPS
Top Edge……………500+FPS

Thanks, that helps  :)

@ KarMeister

I really don't get what you mean by that. Are you saying it is my piston?

#10 karMeister

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Posted 01 September 2008 - 09:33 AM

View Postbrooklyn468, on Sep 1 2008, 08:46 AM, said:

Thanks, that helps  :)

@ KarMeister

I really don't get what you mean by that. Are you saying it is my piston?

lol I was OT.

You really cant tell untill you check your compression parts like your Cylinder-cylinder head,nozzle,Hop chamber.

A huge FPS drop on high level setups ( 140- 170) are commonly caused by broken spings. I have never seen an M120 break tho.

#11 brooklyn468

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Posted 01 September 2008 - 09:48 AM

View PostkarMeister, on Sep 1 2008, 12:33 PM, said:

lol I was OT.

You really cant tell untill you check your compression parts like your Cylinder-cylinder head,nozzle,Hop chamber.

A huge FPS drop on high level setups ( 140- 170) are commonly caused by broken spings. I have never seen an M120 break tho.

I opened up my gearbox and all appears well. I found nothing cracked. Are these cracks supposed to be big?

And how would I tell if my spring is broken?

#12 Shmoogly3

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Posted 01 September 2008 - 11:24 AM

Open up your gearbox and take the spring out. Thats how you can tell if your spring is broken. You look at it! You can tell when glass is broken right, so I think you'll know if your spring is broken.

#13 brooklyn468

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Posted 01 September 2008 - 01:11 PM

View PostShmoogly3, on Sep 1 2008, 02:24 PM, said:

Open up your gearbox and take the spring out. Thats how you can tell if your spring is broken. You look at it! You can tell when glass is broken right, so I think you'll know if your spring is broken.

Well I guess the spring is not broken then.

I have absolutely no idea what is wrong.

Nothing is wrong internally. On the inside, everything is OK. The hop up is fine too.

But when I shoot it, it shoots slower than usual. It only shot through 1 side of a can! The hop up is not working. In fact, it does a negative effect. It makes bbs roll out of the barrel when hop up is turned on. But I look at it when I take it apart, and it appears to do what it is supposed to.

Help me! I am thinking about sending it in... :blink:

And if I didn't say earlier, I use Airsoft Elite .2 bbs, and a 4200 mah 8.4v battery. I also recently rewired to a crane stock. And my tamya connectors suck. I might upgrade to deans... But that is a whole another story.\

Thanks for your help everyone.  :)

#14 vic_man4

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Posted 01 September 2008 - 02:11 PM

View Postbrooklyn468, on Sep 1 2008, 02:11 PM, said:

Well I guess the spring is not broken then.

I have absolutely no idea what is wrong.

Nothing is wrong internally. On the inside, everything is OK. The hop up is fine too.

But when I shoot it, it shoots slower than usual. It only shot through 1 side of a can! The hop up is not working. In fact, it does a negative effect. It makes bbs roll out of the barrel when hop up is turned on. But I look at it when I take it apart, and it appears to do what it is supposed to.

Help me! I am thinking about sending it in... :blink:

And if I didn't say earlier, I use Airsoft Elite .2 bbs, and a 4200 mah 8.4v battery. I also recently rewired to a crane stock. And my tamya connectors suck. I might upgrade to deans... But that is a whole another story.\

Thanks for your help everyone.  :)

Check if theres any breaks, bends or defects in your inner barrel, a ripped hopup bucking, a shot o-ring, or a over lubed barrel/bucking. One of these could be your problem and you should look into it. Good luck with your gun :(

#15 brooklyn468

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Posted 01 September 2008 - 06:26 PM

View Postvic_man4, on Sep 1 2008, 05:11 PM, said:

Check if theres any breaks, bends or defects in your inner barrel, a ripped hopup bucking, a shot o-ring, or a over lubed barrel/bucking. One of these could be your problem and you should look into it. Good luck with your gun :(


And my barrel is not the problem, it was working fine when I got it, and I see no " ripples " in it. I just cleaned my bucking, and I am sure it is not ripped. I may just get a TB just to be safe. I guess that leaves it down to the o - ring...


How would I check my o - ring? Is there any way to check it without taking apart my KM-4a1 again? It is a pain to assemble and disassemble.

If this doesn't work I may send it in. Anyone have word on ASGIs repairing sevices? Do you know how long it takes?

( Allizard beacon shines in the clouds ) I need your help!

#16 brooklyn468

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Posted 03 September 2008 - 03:46 PM

Bump.

I need help before my war coming up.  :unsure:

Edited by brooklyn468, 03 September 2008 - 03:49 PM.


#17 vic_man4

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Posted 03 September 2008 - 04:58 PM

View Postbrooklyn468, on Sep 1 2008, 06:26 PM, said:

And my barrel is not the problem, it was working fine when I got it, and I see no " ripples " in it. I just cleaned my bucking, and I am sure it is not ripped. I may just get a TB just to be safe. I guess that leaves it down to the o - ring...


How would I check my o - ring? Is there any way to check it without taking apart my KM-4a1 again? It is a pain to assemble and disassemble.

If this doesn't work I may send it in. Anyone have word on ASGIs repairing sevices? Do you know how long it takes?

( Allizard beacon shines in the clouds ) I need your help!

Wellllllll, the only way I can think of is dry firing the gun up to your hand to feel the air coming out, if its weak that means your having seal issue and it could be your O-ring, you can buy replacement ones at a lot of airsoft sites. ASGI or anyother place will bang you a lot of money just to open your gearbox. IMO its a seal issue and you should closely examin your airnozzle, hopup unit for cracks, piston head, cylinder, cylinder head, and your o-ring (which is on your piston head). Your best off just taking apart your gearbox and taking the entire upper half of it out and examining it VERY closely!!!!!

Edited by vic_man4, 03 September 2008 - 05:37 PM.


#18 Shmoogly3

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Posted 03 September 2008 - 05:32 PM

Open up your gearbox and move the piston through the cylinder and see if it sticks alittle bit or makes any skid noises like the rubber is sticking to the cylinder when moving. This means you need to lube the piston head and cylinder. My fps went down by 40fps just because my o ring was dry.

#19 brooklyn468

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Posted 03 September 2008 - 05:43 PM

View PostShmoogly3, on Sep 3 2008, 08:32 PM, said:

Open up your gearbox and move the piston through the cylinder and see if it sticks alittle bit or makes any skid noises like the rubber is sticking to the cylinder when moving. This means you need to lube the piston head and cylinder. My fps went down by 40fps just because my o ring was dry.

So is it possible to shoot some lube down the hole in the cylinder in my gearbox?

I'll try that, and check my hop- up again, then get back to you guys. Thanks! :)

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Posted 03 September 2008 - 06:30 PM

Have you inspect your bucking and the nub yet?




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