Well don't take it to heart. When we don't suggest anything, it's safe to assume that we are of the opinion that the proposed suggestion isn't ideal.
I do take it to heart. I come in wanting something constructive, and stupid one-liners coming from mods is REALLY sad.
No offense really, but tar is strong enough already. I do wish it caught fire, but only as a visual effect honestly.
If it caught fire, I'd set the stack at *Whatever number it originally is* and add 2 or 3 to it. Once set on fire, the tarred part will no longer have tarred effects, and will just be on fire.
Spreading fire is interesting, and could offset the high number of stacks it takes to disable a gun, but if you give it a higher priority, you lose the effectiveness some by making engies know they can't leave that fire there else it'll spread. And that timer would need some good balancing, else you risk some OP potential with never ending fires hopping to new components.
If set on fire, give it ten seconds (experimental, if proven OP, change the seconds), and if it isn't gone within that time frame, an object in a vicinity of five meters (again, experimental) will catch fire, and the newly flamed object will have half of the original stack. If
that isn't taken care of, it'll move onto a new object, halved from the second object.
Fire to Hull -> 15 stacks
Fire to Engine -> 7 stacks
Fire to Main Engine -> 3 stacks
Fire to Engine 2 -> 1 stack