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Discussion Starter #1
Have this devilbiss jga 502 paint gun for a long time now it always worked great. Recently had a buddy take it apart and change a few parts on it such as the packing nut and a few other things. When i ran thinner through it i dont get a steady flow it seems to pulsate the material. What would cause this and i notice when i hook up the air to it i hear air hissing around the cap slightly. We put a new washer under the cap and it looks sealed never had a problem with this gun before. Any help would really be appreciated. Thanks
 

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The body of the gun is probably cracked where the fluid tip seats, pull the fluid tip out and look at the seat and thread area and you'll see a hairline crack usually. If the gun body isn't cracked then the needle packing is mostlikely leaking. I used the JGA for quite a few years and the gun body problem is common to the later versions. Let us know what you find.

If the gun is a total loss and a purchase is in your future, definately switch over to a gravity feed design, once you make the switch you'll never go back.
 

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Brian Martin,Freelance adviser
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Some times the fluid tip just needs to be tightened as well. A new gasket could also be needed.

Aaaaa, JGA502 I LOVE those guns. They are like a Fender Stratecaster, darn near sensual in the hand. :)

Brian
 

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ricksautorestoration said:
Have this devilbiss jga 502 paint gun for a long time now it always worked great. Recently had a buddy take it apart and change a few parts on it such as the packing nut and a few other things. When i ran thinner through it i dont get a steady flow it seems to pulsate the material. What would cause this and i notice when i hook up the air to it i hear air hissing around the cap slightly. We put a new washer under the cap and it looks sealed never had a problem with this gun before. Any help would really be appreciated. Thanks
1:Missing or pinched gaskets around fluid nozzle 2: Fluid nozzle or packing not tight,new packings have to be set in place. Tighten packing nut to the point that the needle won't move(doesn't take much)then back off just enough for the needle to move freely. 3: The part of the gun where the air horn screws on will come off.It has its own gasket to and there is only one way for it to go on. I have seen where someone put one of these on wrong.
If air is leaking around cap and the trigger is not pulled,then the gasket around the trigger is leaking. There is no air at the cap without the trigger being pulled.
 

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Discussion Starter #5
not sure what you mean by the gasket around the trigger? when i take the air cap off remove the tip and hook up the air hose i do have air slowly leaking through the 2 holes on either side of the hole where the needle for the fan setting sits. i dont see any cracks in the body as suggested earlier. Would the needle packing cause air leaking in this area? I could not find a new packing locally so we put one in from a parts gun and i'm thinking maybe this wiuld be causing my problems. thanks
 

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ricksautorestoration said:
not sure what you mean by the gasket around the trigger? when i take the air cap off remove the tip and hook up the air hose i do have air slowly leaking through the 2 holes on either side of the hole where the needle for the fan setting sits. i dont see any cracks in the body as suggested earlier. Would the needle packing cause air leaking in this area? I could not find a new packing locally so we put one in from a parts gun and i'm thinking maybe this wiuld be causing my problems. thanks
The rod that comes out of the handle of the gun that the trigger pushes in. There is a gasket in there. Either the gasket is messed up or the plunger leaks. No air at cap unless trigger is pulled.
 

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Paintshop Dog
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MARTINSR said:
Some times the fluid tip just needs to be tightened as well. A new gasket could also be needed.

Aaaaa, JGA502 I LOVE those guns. They are like a Fender Stratecaster, darn near sensual in the hand. :)

Brian
Careful Martin you're showing your age! :D
Kinda feels ... ...well, I just won't say how it feels in my hand. :p

Sounds like these guys got the problem figured out though.
 
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