All of the suggestions posted so far are excellent. And of course, Todd can always get to the root of the problems and helps anyone who asks. And the different generation MESs do require different approaches because Masterbuilt changed things with every generation - and not always for the better.
I live at about 5200 feet, and have what seems to be called a "newer" Generation 1 MES 40.
I had problems keeping my pellets lit at first, but have largely overcome my issues by using all of the suggestions listed above.
Here's what I do:
NEVER use water in the smoker. Keep things dry.
I leave the chip loader completely out of the unit. That leaves the air entrance totally open.
I leave the chip drawer pulled open at least an inch so there's a path for air to flow in the entrance, over the heating element, and then out into the smoker.
I set the AMNPS up on the two rails on the left side of the smoker so that it's elevated for proper airflow up under it.
I always have a foil drip shield of some sort above the AMNPS to prevent drips from reaching the pellets.
I microwave the pellets for 30 seconds. Then stir them for a minute or so with a large spoon. Then I repeat that process about five times. I can feel the warm humidity leaving the pellets as I stir them each time. You need to get the things dry! But do be careful. I've had them ignite in the microwave oven when I nuked them for more time all at once with no stirring. It smoked up the microwave oven pretty badly! Don't walk off and leave them nuking!
Ideally, I put the pellets into the AMNPS, and put it in the MES while it's heating up. If the pellets can bake in the MES for a half hour or more, that helps dry them even further.
I blowtorch the living daylights out of the end of the pellets in the AMNPS. Even after they look like they're going, I roast them more. Fry them good with the blowtorch!
I let them burn with an open flame for five minutes or more, then blow them out and again blow on the cherry to really get it going good.
That has worked very well for me at this high elevation with this gen 1 MES-40.
BUT, if I try to run the smoker at too low of a temperature, the draft/draw through it is still too lame to keep the pellets supplied with enough oxygen to burn reliably. I recently did a batch of Jerky, and because I had the smoker set to only 150 to 160 degrees, and because it rained while I was doing this run (just my luck!), and perhaps because of the huge surface area of the wet jerky adding a LOT of moisture to the system, the pellets went out.
But I think I have one possible answer.
I mounted some magnets to the four corners of a small computer cooling fan and now I can just slap that fan onto the side of the smoker and have it blow into the air inlet. Again, since I never use the chip hopper, it's completely removed from the smoker. By adjusting the position of the fan with respect to the air inlet, I can adjust the amount of air flow. With it centered directly over the hole, things were perfect for the dehydration phases of the jerky-making. But that may well be far too much air flow for the smoking phases of jerky, or for normal smoking of meat or cheese, etc. But if I just slide the fan over so it's offset from the opening to some degree, I can get less air flow.
So forced air may be an answer for some people in some situations. I actually started a thread about this earlier last night. It's here:
At some point, I will probably build a mailbox mod, too, though, because it will be helpful when cold-smoking cheese, and it's a good way to get cleaner smoke with the heavy creosote condensed out before it can get to the meat.
Best of luck with it. These MESs can be frustrating, but once you figure out the formula that works for you, in your location, with your particular version of the MES, the AMNPS produces great results. It's made all the difference in the world to me with this smoker.
The jerky did come out just great despite my troubles during that run. With the fan stuck over the air inlet, the final dehydration of the jerky went beautifully!