Hiyah,
I have an 8mm single shot Marushin Carbine, are you sure it has a fixed hop in the barrel? Because mine doesnt. Just the one at the breech end of the barrel. Have you tried firing the gun without any ammo loaded? does a lot of air/gas come out of the barrel? Poor power might come from poor seal contacts, ie not as much gas is making it down the barrel. A good test would be to put something light and roly, (like a ping pong ball) infront of the barrel and shoot with no ammo inside, so if it shoots off, the seals are good.
If it does, but the BB still falls out in a lame way, it's probably your hop. You could try and contact Marushin directly, I'm sure they have a customer services, see whether you can get a replacement part.
Another thing to check, is whether the 'O' ring is still sat inside the top of the magazine, as one fell out on one of my mags, and the performance is rubbish without it.
The one inside the barrel is called "flat tradjectory" I think, and you can remove them (speak to Barrie and Anne on the forums) they did it with the M2 which also has the FT hop.
The O Rings are quite standard, you can get packs of various sized ones at most hardwear stores.
Will wait to see the pics.
Hi Jay,
I am not familiar with the single shot version but with my blowback version there are two hops......one fixed hop near the muzzle and the normal adjustable one at the breech. Have a look into the breech end of the barrel and see if there is a small circular hole or cutout at the 12 0 `clock position (top) of the barrel. if so there is a small grub screw in there which is the adjustable hop. You insert an allen key in the hole and screw or unscrew it to give your hop. This hole runs parallel to the barrel ,i.e above it at 12 o`clock ( looking from muzzle to breech end.
Hope this helps.
flatrajectory
"REMEMBER, LIFE IS NOT A REHEARSAL"
Glad you got it sorted NJay 
