furnaceTimer

local s = true
local burntime = 40
local offset = 3

function wait( n )
    local myTimer = os.startTimer(n)
    while true do
      local event, timerID = os.pullEvent("timer")
      if timerID == myTimer then break end
    end
end

turtle.dropDown()
turtle.suckDown()
wait(burntime - 1)
turtle.dropDown()
wait(2)

while(true) do

    if s == true then
        turtle.suckDown()
        s = false
        wait(burntime - offset)
    else
        turtle.dropDown()
        s = true
        wait(offset)
    end

end

print("Should see this...")