If you can stand a little tobacco in your joint, mix some in, maybe about 10-25% cigarette tobacco. That seems to make the joints burn nice and smooth without any major runs. I guess the downside is that modern cigarette tobacco has been chemically engineered to burn "just right," so you're getting some of those mystery chemicals in your joints if you do that.
I can't swear this is true, but a dude who worked in a car repair shop told me years ago that American cigarettes were "designed" so that if you drop a lit one on the car floor while you're driving you don't have to worry about picking it up because it will stop burning if you are not hitting on it. That was nice to know because I was still a cigarette smoker back then and was constantly dropping burning Camels in between my feet while driving the freeway. The repair dude told me not to even worry about that, because it would not start a fire.