Hope this may help. Been heating with and installing wood stoves for 50+ yrs. Currently Jotul Combi 4 (shop), Jotul 118 (house). Before you spend a lot of money, 3 actions-make sure chimney cap spark arrestor is clean not hindered. Move stove and run straight pipe to double wall. Remove elbow and check for draft. Check stove interior for any possible blockage of draft and air intake systems. Heat shield at riser and tread.
Realize you have probably already tried this. Just thought I'd mention them.
Burning, smoking paper at open insulated stack to check for draft. I feel your pain Have not had your problem with any of my stoves or the ones I have installed. Wish you much luck. I do not see a problem but I did not like that elbow.
Al Robertson
