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

Hareton · 13-08-2012 11:06pm #1

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.

DeBurca · 13-08-2012 11:46pm

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

Hareton · 13-08-2012 11:54pm

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.

Hareton · 17-08-2012 3:38pm

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

$kilkenny · 17-08-2012 3:40pm

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

Hareton · 17-08-2012 4:03pm

$kilkenny wrote: »

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

Brand new

Stercus Accidit · 17-08-2012 4:26pm

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

Hareton · 18-08-2012 6:08pm

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

$kilkenny · 18-08-2012 6:26pm

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

Stercus Accidit · 18-08-2012 11:23pm

$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.

DeBurca · 19-08-2012 12:02pm

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 ??????????

Hareton · 19-08-2012 1:00pm

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.

DeBurca · 19-08-2012 1:53pm

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

Hareton · 19-08-2012 8:13pm

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.

DeBurca · 20-08-2012 12:17am

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

Hareton · 20-08-2012 12:36am

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??

$kilkenny · 20-08-2012 9:29am

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

sci-ops · 20-08-2012 9:51am

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?

Hareton · 20-08-2012 9:58am

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.

DeBurca · 20-08-2012 11:26am

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

Hareton · 20-08-2012 6:29pm

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

Stercus Accidit · 20-08-2012 7:57pm

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.

DeBurca · 20-08-2012 8:38pm

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

Hareton · 20-08-2012 8:45pm

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

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

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