Without seeing the hand tossed glides it's difficult to give advice.  If it is nosing in...gurney flaps on the bottom of the trailing edge of the horizontal stabs will increase the nose dive in effect giving more down elevator. 

If it's stalling, then the gurney flaps on the bottom might help.  These catajet don't float in their flight patterns so it will need some speed to glide but you should be able to get a fairly flat level glide to a gentle landing.  You might try ungluing the horizontal stabs and relocating them in a more zero/zero decalage arrangement. Consider this a learning model and proceed from there!
Sky9pilot

No, I was totally unsuccessful with the hand launch phase. I then moved to low powered catapult launches, at least what I considered low powered, based on previous experience. Basically, I'm still not using full power. However I will reduce power more and see what happens. If nothing, else this little beast has proved durable over a grass field.

I have not been able to measure the decalage (?). But it looks like the horizontal stab is considerably more than 1 degree negative relative to the wing. I have seen an article by Gary Morton promoting a 0/0 degree alignment of the flying surfaces with adjustments using Gurney flaps.

If the lower powered catapult launches do not get where I need to be then I'll build another with a modified wing/tail alignment.

Thanks for the thoughts.

Whipped up an F-4H jetcat of about a 6” span from a plan preceding the digital age. Currently it launches almost arrow-straight with a great climb and then noses over for a lawn dart landing. Launches are from level to perhaps about a 30 degree elevation. I can’t launch at a higher angle because it goes overhead and I lose track of it. Doesn’t seem to make any difference if I launch with it banked to the right or more or less level.

It was built with the wing cocked to the left ( not recommended)  which resulted in a nifty roll to the left followed by a “falling leaf” maneuver. A trim tab on the left wing neatly solved that problem. Now it flies like an arrow. Not ideal but at least it flies. All that walking is good exercise.

And to think that if I wanted a glider with no turn at all, I probably couldn’t build one!

Should I keep adding clay to the nose?

This Day in Aviation:
Thought you might find this interesting: Bendix Trophy Race Click Here

And here's an F4H-1 forsale ...a civilian F-4 Phantom II.  Who would have thought!

I have been working on a plan for an F-4E that could easily be converted to the F-4H-1 version. Here's a link to our plans on Free Flight Archive: Click Here

Volare Model Products has a kit for a catapult glider F-4E: CLG F-4 kit