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Low fps........... baffled.

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  • 14-08-2012 12:06am
    #1
    Hareton
    Registered Users Posts: 1,215 ✭✭✭


    Really lost on this one. rif is putting out around 240fps with an m90 spring. air seal was done to the last. have the correct cylinder to barrel ratio. really dont know why its so low? any ideas people. put alot of work into the gearbox and its frustrating at this stage.

    cheers.


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    #2
    DeBurca
    Registered Users Posts: 9,746 ✭✭✭DeBurca


    If you are sure that all within the gearbox is good then it has to be in the air-nozzle/hop-up combo

    Are you sure that the air-nozzle is the correct length so that it seals against the hop-up rubber

    Is the hop-up unit fully engaged in the front of the gearbox

    Is the tappet plate moving fully forward to allow the air-nozzle to seat properly against the hop-up rubber


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    #3
    Hareton
    Registered Users Posts: 1,215 ✭✭✭Hareton


    yea just notice the tappet plate is angled back where is jois with the air nozel.
    Where all the other tappet plates i have lying around are virtually 90 degrees. probably the problem. cheers.


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    #4
    Hareton
    Registered Users Posts: 1,215 ✭✭✭Hareton


    New tapper plate did nothing and air nozzel is the same size as the last one.


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    #5
    $kilkenny
    Registered Users Posts: 717 ✭✭✭$kilkenny


    ger is the M90 cut or anything??
    and did u buy it new?


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    #6
    Hareton
    Registered Users Posts: 1,215 ✭✭✭Hareton


    $kilkenny wrote: »
    ger is the M90 cut or anything??
    and did u buy it new?

    Brand new


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    #7
    Stercus Accidit
    Registered Users Posts: 8,758 ✭✭✭Stercus Accidit


    Is the piston head too tight in the cylinder maybe? That can cut down on FPS as the piston struggles to move forward.


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    #8
    Hareton
    Registered Users Posts: 1,215 ✭✭✭Hareton


    Stercus Accidit wrote: »
    Is the piston head too tight in the cylinder maybe? That can cut down on FPS as the piston struggles to move forward.

    No that's fine. Still can't get it any higher than 250fps


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    #9
    $kilkenny
    Registered Users Posts: 717 ✭✭✭$kilkenny


    have ya tried a completly different spring??
    maybe its just crap or a complete lemon.


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    #10
    Stercus Accidit
    Registered Users Posts: 8,758 ✭✭✭Stercus Accidit


    $kilkenny wrote: »
    have ya tried a completly different spring??
    maybe its just crap or a complete lemon.

    That could be it, m90's can be very weak in certain set-ups.


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    #11
    DeBurca
    Registered Users Posts: 9,746 ✭✭✭DeBurca


    You need to test to see if air is leaking due to the air-nozzle not seating properly against the hop-up rubber

    You can do this by removing the mag and turning the gun upside down and holding the magwell close to your face while firing
    You will feel if any air is escaping through the feed tube of the hop-up unit
    If you feel air escaping then you know that your problem is in that area

    If you feel no air leak then the problem has to be in the gearbox
    So maybe the problem is as others have said connected to your new M90 spring

    Also what length inner barrel are you using and what type cylinder have you ??????????


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    #12
    Hareton
    Registered Users Posts: 1,215 ✭✭✭Hareton


    DeBurca wrote: »
    You need to test to see if air is leaking due to the air-nozzle not seating properly against the hop-up rubber

    You can do this by removing the mag and turning the gun upside down and holding the magwell close to your face while firing
    You will feel if any air is escaping through the feed tube of the hop-up unit
    If you feel air escaping then you know that your problem is in that area

    If you feel no air leak then the problem has to be in the gearbox
    So maybe the problem is as others have said connected to your new M90 spring

    Also what length inner barrel are you using and what type cylinder have you ??????????

    363 inner barrell and the cylinder is ported to the rear.


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    #13
    DeBurca
    Registered Users Posts: 9,746 ✭✭✭DeBurca


    Hareton wrote: »
    363 inner barrell and the cylinder is ported to the rear.


    How much to the rear ???????
    Can you post a photo

    Have you checked to see if air is leaking from the hop-up unit


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    #14
    Hareton
    Registered Users Posts: 1,215 ✭✭✭Hareton


    Couldnt feel anything out of the hop up. even put the thinest smallest piece of tissue paper over the hop up and not a budge. would the fact that its a non linear spring make any kind of difference.

    here's the pic.


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    #15
    DeBurca
    Registered Users Posts: 9,746 ✭✭✭DeBurca


    Well as you say that the paper did not move then all is grand there
    The cylinder is perfect for your barrel, so that just leaves the gearbox

    A non liner spring will not effect the FPS, its just makes life easier for the motor to get up to speed
    It would seem the you have an air leak within the gearbox

    I would first check the piston head O-ring by doing a compression test without the air-nozzle
    If all is good then repeat the test with the air-nozzle attached so as to check if air is escaping between air-nozzle and the cylinder head brass pipe
    Do the air-nozzle test with the air-nozzle in both the retracted and extended position


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    #16
    Hareton
    Registered Users Posts: 1,215 ✭✭✭Hareton


    DeBurca wrote: »
    Well as you say that the paper did not move then all is grand there
    The cylinder is perfect for your barrel, so that just leaves the gearbox

    A non liner spring will not effect the FPS, its just makes life easier for the motor to get up to speed
    It would seem the you have an air leak within the gearbox

    I would first check the piston head O-ring by doing a compression test without the air-nozzle
    If all is good then repeat the test with the air-nozzle attached so as to check if air is escaping between air-nozzle and the cylinder head brass pipe
    Do the air-nozzle test with the air-nozzle in both the retracted and extended position

    Done all that before assembly. Cylinder head is Teflon taped o ring air nozzle. Compression is spot on a lot of effort need to move the piston when it passes the port. Really only leaves the spring then doesn't it??


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    #17
    $kilkenny
    Registered Users Posts: 717 ✭✭✭$kilkenny


    the gun fluctuates by 2fps, around 240-242 in the chrono witch is amazing so its deffinatly not an air leak.


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    #18
    sci-ops
    Registered Users Posts: 1,050 ✭✭✭sci-ops


    Hi Hareton,

    I'm going to ask a stupid but obvious question, what weight bb are you using and is the chrono configured for it?


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    #19
    Hareton
    Registered Users Posts: 1,215 ✭✭✭Hareton


    sci-ops wrote: »
    Hi Hareton,

    I'm going to ask a stupid but obvious question, what weight bb are you using and is the chrono configured for it?

    Ha .2g and the chrono was set for it.


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    #20
    DeBurca
    Registered Users Posts: 9,746 ✭✭✭DeBurca


    If the compression is all good then it must be the SPRING as has been mentioned several times already

    Why fit a new M90 spring ?????? was the old spring broken/damaged in any way
    Can you refit it and do a comparsion test to see by how much the FPS changes


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    #21
    Hareton
    Registered Users Posts: 1,215 ✭✭✭Hareton


    DeBurca wrote: »
    If the compression is all good then it must be the SPRING as has been mentioned several times already

    Why fit a new M90 spring ?????? was the old spring broken/damaged in any way
    Can you refit it and do a comparsion test to see by how much the FPS changes

    Put in a different spring. Not sure what strength. Can see a power increase. Haven't chronod yet. Now the motor and battery get really hot when firing. Checked the wiring then checked again. No shorts or splits in the wire. Any ideas? Tried firing with the previous spring again and no over heating


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    #22
    Stercus Accidit
    Registered Users Posts: 8,758 ✭✭✭Stercus Accidit


    Ported cylinders deliver lower fps in my experience than non-ported in mp5 length barrels, combined with an m90 which is a weak spring and that's your problem. I've used m90's in long AK barrels with full cylinders and gotten low fps, you dont sound like you have an air leak.

    For a 363mm Barrel (m4?) I don't think you need a ported cylinder, so either lose the m90 or the ported cylinder.
    Hareton wrote: »
    Put in a different spring. Not sure what strength. Can see a power increase. Haven't chronod yet. Now the motor and battery get really hot when firing. Checked the wiring then checked again. No shorts or splits in the wire. Any ideas? Tried firing with the previous spring again and no over heating

    Typical if the motor is under heavier strain, I get that on many of my guns too, maybe get higher guage wiring or a higher torque motor.


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    #23
    DeBurca
    Registered Users Posts: 9,746 ✭✭✭DeBurca


    Hareton wrote: »
    Put in a different spring. Not sure what strength. Can see a power increase. Haven't chronod yet. Now the motor and battery get really hot when firing. Checked the wiring then checked again. No shorts or splits in the wire. Any ideas? Tried firing with the previous spring again and no over heating


    Your motor is getting hot due to the extra load being placed on it by a stronger spring
    If the motor has to work harder to compress a stronger spring then it will draw a greater current from the battery which will in turn get hotter

    So if a different spring is giving a power increase it looks like your problem has always been the spring


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    #24
    Hareton
    Registered Users Posts: 1,215 ✭✭✭Hareton


    DeBurca wrote: »
    Hareton wrote: »
    Put in a different spring. Not sure what strength. Can see a power increase. Haven't chronod yet. Now the motor and battery get really hot when firing. Checked the wiring then checked again. No shorts or splits in the wire. Any ideas? Tried firing with the previous spring again and no over heating


    Your motor is getting hot due to the extra load being placed on it by a stronger spring
    If the motor has to work harder to compress a stronger spring then it will draw a greater current from the battery which will in turn get hotter

    So if a different spring is giving a power increase it looks like your problem has always been the spring
    Ah rite. Thanks for the help guys


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