Tamiya

How do we fix this front downforce problem?

Joax aside, it might not be a front downforce problem. You have rear-loaded aero on that (deliberate or not) which means as you speed up you're probably starting to get downforce rearward of the rear axle. That unloads the front axle and makes the steering light. The front then loads up again unpredictably as the car slows back down. You could put your gps unit ahead of the front axle, but you're probably going to make it start to porpoise as a result. If you're going to put it anywhere, make a space for it in the middle of the car even if it's in the cockpit area.

I've said it before, you should re-make that chassis pan without the holes, especially at the front and under the car. Cut it in as tight to the wheels as you can get it. You want it running a bit of rake, so slightly higher at the back than at the front. If you can get the middle part of that floor doing the bulk of the work for you, you'll be generating downforce in the middle of the car where it's predictable and with very little drag penalty. At the moment it's letting all that air spill into the car unpredictably and the big raise at the back is probably the only bit doing any work.

Just Gaffer tape it up on the top surface for now to see if it works. Maybe put a fillet of Plasticine or tape round the front to seal it to the floor, to block the air from going into the body under the front.