I just noticed your “business card thickness” description of the mouth. That should be adequate. At the very least, you should be able to adjust for a shaving thinner than that so that the mouth opening isn’t an issue; however, I think the opening you describe would be adequate no matter what.

Also, once you take care of the jamming issue, inspect the blade width relative to the width of the plane body. On old planes, it is typical for the body to have shrunk. Since steel does not shrink, the blade will be too wide and will not quite match the shape of the bottom, either. So, somewhere along the way, you’ll want to correct this. You can do some work with the plane in that condition, but it isn’t ideal and, for some profiles, the blade hanging out wider than the plane body will lead to gouging that will spoil the profile being cut.

I second Ed’s suggestion regarding the wedge. I was recently working with an old moulding plane and was experiencing the same issue. Shavings would get jammed in front of the blade within a stroke or two no matter how much I sharpened and fettled the blade. I then compared every aspect of the plane with another (different profile) that worked wonderfully, and realized that wedge on the good plane tapered to a point, whereas the problem plane’s wedge had a more blunt tip, maybe 1/16″ wide. I used my chisel, bevel down, to refine the tip of the wedge to a point as thin as I thought it could go without breaking … and viola! Problem solved. I was amazed at how such a little thing caused so much of an issue. After that the shavings came curling off as they should, and I was able to plane the entire profile on my stick of wood without stopping once to clear the blade!

I shy away from construction wood with visible resin pockets, as the resin tend to clog up everything, including my patience. That does of course not exclude a diffuse distribution of resin extractives as the cause to blocking the mouth of the spokeshave. Yet, the Scots pine I use has a nice fragrance of resin (the kind chewed upon during innocent childhood), but its shavings cleared the original mouth opening.

Someone once told me (Probably Paul or Charles Neil) that pine needs to be heated to a certain minimum temperature or else the resin remains sticky, which can affect finishing. I do not know if this is true for spruce as well. This is why I asked if the wood was air dried (which would not ever be hot enough). I’ve always meant to look up info about this, but still haven’t done it. And, it isn’t a matter of the construction SPF vs. quality pine. I had some wonderful eastern white pine that was air dried….and drove me insane during finishing with an oil based finish as it would not dry until I used some alchemy.

Excellent! Another trick is to blacken the back of the blade, maybe with a sharpie. Even better is to use layout dye. Then, load the blade into the plane and set the wedge. Now, trace the profile of the sole onto the back of the blade and use it to guide you when refining the shape of the blade. In this way, you can get excellent agreement between the two.