Yep it's always a bit of a problem when the new fuel line is about the same length as the old line and with some old fuel tank rubber grommets going hard and some rubber shrinking , sometimes you need to replace the grommet but probably not worth spending $10. for 5 grommets unless you're fixing a few snippers .The other way is to glue the old grommet in with some Stag Jointing Paste and block the holes in the grommet then drill 2 holes in the top of the tank.
Sometimes after cleaning the fuel tank out and using a clean filter they still run a little rough and just pushing the primer multiple times as the snipper is running is enough to clean the old gummed up fuel out of the carby and they run fine again with no adjustments and then some take a little more work to get running right.
"The manual change head says 3mm only but only had 2.5mm line and it worked well. Will I wear out the alloy using undersize line?"
I assume the 3mm only is for safety issues so the line doesn't flex too much if it's smaller than 3mm , just so it doesn't move around more if smaller and come loose and fly out of the cast alloy head. I'd say the 3mm line will lock in better in the alloy head.
I've got a few of these snippers and you can use an old Ryobi RCT2800A Grass Scorpion Whipper snipper cutting head on a bent shaft snipper that replaces the alloy head or just use the cutter half shaft from another snipper as these join in the middle then you can use a bump head.
The general rule with string trimmer line size is that the tougher the application, the thicker the line needs to be. A larger diameter line increases the power and durability of the line, which leads to less breakage and wear-out
Thinner string requires less power to spin up to speed, and for “just grass”, a . 080 ( 2mm ) is just fine. You can let more string out, and more of the engine's power is available for cutting, as less energy is needed to rotate it.
For light work, such as trimming grass, 0.065″-0.085″ should be sufficient. For thicker grass and weeds, a line in the 0.085″-0.110″ range will get the job done, and for thicker underbrush, anything thicker than 0.110″ will work.
