inseters sometimes get stuck trying to put fuel into things that have another type of fuel in them
Ex: trying to put wood into a machine that currently has coal in its fuel slot.
when this happens it gets stuck because it cannot put in the wood because coal is already there and the coal cannot be used because the inserter is not putting in the ingredient to make the machine go

Also, do not know if it is relevant but I am using the mod good burner things to add burner assemblers

Yes, that is something i experienced myself and i plan to fix it when/if i find some spare time for modding aggain.
Until it is fixed, the recommended workaround is to avoid mixing of fuels.

Thanks for the report.

I went ahead and fixed the bug, I have tested it and submitted a pull request to github.
Please accept and push to the mod portal

-DK

Thanks for the pull request. Looks like i somehow missed can_insert in the API docs. I'll update the mod soon.

It may have not existed at the time

Reading the API, i got the suspicion, that i will have to do an additional check for the amount of items wich can be inserted as it says, that the bool only indicates whether at least one of the items can be inserted.
So inserters could still get clogged with the remaining items of a stack if i don't limit them to stacksize 1 for refuelling (wich would make me sad). But it should still be better for performance to call can_insert first.

I don't have time for experimenting with LUA right now. But i started a thread about the best way to do it anyway (so that i can dive right into doing it if i suddenly aquire some free time):
https://forums.factorio.com/viewtopic.php?f=25&t=78737

the stack size thing is a problem but it is one that existed before I updated the mod

Yes, that is an old one - but i did not see it before. There are two naive and obvious ways to fix it, wich should work. So that bug is about to be fully fixed - maybe next saturday or sunday.

cool Thanks