Vacuum sealer won't evacuate small bags

[C00P]

We have a "Campfire" vacuum sealer. Used it a few times successfully before now but not much.
Decided tonight we would vacuum seal a heap of meat and freeze it for a long trip.
Funny thing, the sealer would evacuate the large bags (almost full width of the seal) but not small ones (half the width of the seal).
Checked the sealer gaskets- all appear OK.
Double checked we were not putting the end of the bag over the hole where the air is pumped out.
Listened for intake of air when the vacuum area was opened- heard the usual hiss, so the vacuum pump is sucking the air out of the vacuum chamber OK but isn't getting the air out of the bag.
Sealed a bag full of mostly air and plunged it under water in the sink- no bubbles, so the bags were not leaking.
Cleaned out one of the failed bags and ensured the inside of the top of the bag wasn't greasy or sticky- still would not suck the air out.
Tried pressing on one of the bags while the vacuum was operating- couldn't force the air out of the bag. (Stopped the process before the sealer came on, and the top of the bag was still open when we removed it from the machine.)
This really doesn't make sense-why will it suck all the air out of a large bag, but not a small one?
Any ideas? It's got me baffled!

Coop

[Blknight.aus]

could be the air is getting into the evacuation chamber around the edges of the bag.

[Grentarc]

could be the air is getting into the evacuation chamber around the edges of the bag.

I have a sunbeam one and smaller bags require me to press down on the top of the machine to get a decent seal, then it quickly evacuates the bags.

[C00P]

could be the air is getting into the evacuation chamber around the edges of the bag.

Good suggestion, but if this was the case there would be no hiss when the chamber is opened. And the big bags have the same edges just further apart.

Coop

[C00P]

I have a sunbeam one and smaller bags require me to press down on the top of the machine to get a decent seal, then it quickly evacuates the bags.

Will give that a try next time we use it,
Thanks,
Coop

[Grentarc]

Good suggestion, but if this was the case there would be no hiss when the chamber is opened. And the big bags have the same edges just further apart.

Coop
Mine create little bit of a vacuum but then the pressure differential must be enough for the seal to not work as my bag deflates a small amount, then just sits there. My seals look good, but it never did this from new, only after sitting for about a year.

I do prefer the in chamber one at my work though.