Charcoal gasifiers also rely on a range of reactor body sizes, you don’t want to go too small depending on the engine. The main dimension is the nozzle, because a charcoal gasifier is really making Air Gas. The hot charcoal is robbing any oxygen molecules it can find and leaves you with CO, Nitrogen, and Hydrogen from moisture in the air and from any water drip you add to the nozzle.
With a charcoal gasifier you gain a bit of self insulation from the fuel, carbon makes a very good insulation. That’s the main reason why you don’t want to use too small of a reactor body.
Eddy Ramos has made a very nice guide to building an updraft charcoal gasifier, it includes a formula to configure your ideal nozzle size.
Here’s a direct link to download the PDF in English:
Bear in mind with updraft, you want your charcoal to be in the 1/8" to 3/4" cross section size range and to be very dry. It also must be entirely converted to charcoal, brands(halfway between wood and charcoal) should be tossed into the next batch for charcoal.
With an updraft, any tar made will go upwards with the gas.
A cloth bag filter works very well to catch any tar, and it will instead clog the filter to save the engine.
Also in an updraft, the exiting gas is almost ambient until you begin to be low on fuel, the unreacted charcoal above the active zone slows down the exiting gas and allows it to cool down.
What diameter of reactor body were you thinking of using? For that engine size I’d go with no less than 14" in diameter, with my 2 Liter Mazda pickup I used a standard 55 gallon drum of 22" diameter.
If I may add, a 1.3 Liter engine is plenty big enough to run a raw wood gasifier efficiently.