In my opinion you have a fuel problem. Your anecdote shows this.
You sayd you had to shake the grate to clear ash in order to keep the flare going, but l think thats not what happend. The oposite, you may lack fines in your fuel! After a while, the smaller char burnt and left you with bigger stuff. This can not reduce the gas propperly and you are left with hot and moist gas with lots of CO2. Shaking the grate shook some new fines in the charbed, making it tighter. The fact that the fan sped up also prooves this, since more restriction on the suction side causes the fan to spin faster, not slower. Counterintuitive…
You realy need what we call engine grade charcoal for any gasifier. Idealy, you want half inch charcoal bits with all the voyds between the bits filled with finer stuff, but with no dust! If that makes sence… and do not go over 20% moisture.
Going simple fire might not be the solution for you. Updraft gasifier are even more picky on fuel quality and size. And they can only crack water if its added in the nozzle, all the water in the charcoal just gets boiled off and sucked in the sistem.
And even using bone dry charcoal still contains about 10% moisture, from air and cooking process.
Downdraft is far superior in this as its the only way possible to make 100% dry gas.
Many say damp gas is not a problem, afterall the moisture will condensate out in the cooler and filter. But l disagree. Yes, the fog will condense, but not the relative moisture in the gas. We must not forget that we operate at a vacuum and that the gas is warm, meaning the amount of water in the gas that has been wet and then dryed is not the same as if we do this at room temperature and pressure. I belive l once calculated that in such a gas, the water vapour content is around 10% vol of the gas! Thats water we can never condense out, no matter how big of a cooler we got. And thats 10% added to the 55% of other inert gases in woodgas, nitrogen and CO2.
I belive its best to tune the gasifier and fuel to a point where litle or no water escapes the charbed. It realy does make a difference, specialy in flame speed!