keystoker a120 shuts down on high limit

hoping someone can give me some info. i have had a keystoker a120 for a few years now and it has almost been faultless. this year when i fired it i discovered the combustion blower was bad so i replaced the dayton blower with a fasco straight from keystoker. now since i have replaced the blower i have been having a problem keeping it lit. it will run for a day sometimes less and then it shuts down on the high limit at over 200 degrees. and by the time it cools down it goes out. the distribution blower is running but i assume not enough to take the heat out. the fins are clean filters clean, and nothing has been changed from last year except for the blower and a complete cleaning. does anyone have any insite on what may be happening. i have replaced the aquastat with the honeywell timer also but that was 2 years ago. could it possibly be my thermostat. i have a digital honeywell but it is by no means a high dollar unit. any help would be appreciated.

Does the new Fasco blower have the intake blockoff plate? It should only be open 1/2 way or so unless the A120 is different than a Koker. Also with the convection blower running on high, you should be cooking yourself out of the house with a firebox hitting high limit. You can check the t-stat easily by seeing if when selected off you still have coal feeding in.

Good point on the comb. blower cover, but I think it's blower motor related. Make sure your blower motor isn't going off on thermal overload. Also, you don't have any return air grilles blocked?