1983 Vigilant sealing questions

[Rabidsquirrel]

Hello all,

I started to disassemble my stove (1983 Vigilant) because of issues with achieving a horizontal burn. I have approximately 20'+ of 8" chimney. The stove is air tight and passes the light test. I start my normal vertical burn and get the griddle 500-600ºF and chimney temps ~400ºF. Draft is more than satisfactory, I don't have a problem opening the top when in vertical burn. I close the damper with the keyhole airway fully open and almost immediately the temperatures start to drop until the chimney gets to be around 200ºF after about 10 minutes. It definitely seems like the stove is starving for air, because if I crack the griddle open during horizontal burn the wood springs back to life with flames.

At this point I can open the damper again, get the temperatures back up and repeat the process and once again the temperatures take a nose dive. My wood is hardwood, seasoned, and between 8-15% moisture. I'm generating way too much creosote burning at these low temperatures, so I decided to start ripping stuff apart to clean everything out and to make sure I don't have any blockages in the keyhole airway.

I removed the damper, upper and lower fireback, and noticed this large gap around the keyhole airway:

Should that circled gap be cemented closed? It seems to me that instead of air being sucked into the fire box most of it will be sucked right up the chimney with the draft. Here is a second picture with a flashlight shining directly into the keyhole:

Thank you for all your help, and I hope my issue is as simple as resealing some parts of the stove.

 

[Rabidsquirrel]

Well, I sealed everything up, and I'll give it a small burn tomorrow morning to help cure the cement, and then I'll do a larger burn.

I see multiple mentions of the secondary air feeding the 5 little holes in the fire back, but what I saw with the stove ripped apart and an exploded diagram of my stove doesn't really support that.

I marked up the exploded diagram with what I believe is going on, maybe someone can correct me:

To me it looks like the primary air feeds the primary tube (5), and the cover plate (47) which in turn feeds the air horn (43) and the 5 holes in the fire back (40). The secondary air feeds only the night air tube, behind the night air cover(3). If I understand this thing right, both the night air and the air horn feed the horizontal burn. I still don't understand how the secondary air is fed into the stove though. It seems like any air introduced by the night air tube would be drawn right up the chimney before it makes it to the 5 holes in the FB.

Thanks for your replies.