My 74 dt 175 and 360 are usually used for tooling around town, but recently I have doing some aggressive trail riding, some small jumps and stuff, The front forks bottom out easily. Are they just worn out or can I get a stiffer spring? I have changed the fork oil , no change. Is there a high performance option?

First be sure they're bottoming out by noting where the dust scrapers leave a mark.
Sometime using oil that is too heavy slows the action so much that they thud even though not bottomed out.
They Just go thud because the oil can't get away quick enough.
Not sure what springs are availeable for those but hope others know.
When sitting on the bike how far from topped out do you think they are.
Probably only have about "7 of travel to the very bottom, but subtract the last inch or so where it traps the oil so you don't get a metal to metal clang.
Then subtract the first inch or two if softly sprung sitting on & doesn't leave a lot of usefull movement.
Ok that's exagerating a bit-- but!!.
Should be a spacer on top of the springs which you could make longer ones of, but got to be very careful not to end up with the springs coil binding on compression before the forks reach the bottom.

What oil did you put in the forks?

I don't think I should  be able to sit on the bike, apply the front brake and push down on the handle bars and completely compress the forks.

Yes, what oil and do you have the specified amount of oil in the forks. Unusual to have soft forks on two bikes.

DW68 wrote:  I don't think I should  be able to sit on the bike, apply the front brake and push down on the handle bars and completely compress the forks.

I don't think the best way for you to hopefully find an answer to your problem is to respond to the questions RT325 asked you with nothing but more complaints...  (and by the way, he's quite an expert and has probably forgotten more about these bikes than any of us could ever hope to learn... )

So I guess we're both out of luck. 

Hey, all good. I just started typing untill someone came along with a better idea lol.
But agree that you shouldn't be able to sit on it & bottom out the way you said.
Best see what's out there in aftermarket springs.
Even new originals might be an improvement.
Check out the original spacers to see if they look shortened [hacksaw marks] or shorter homemade ones fitted.
We tried air valves in the caps with limited success.
Even ran total air & no spring for a bit in my MX250B "75. [MX bike]
Experimental time those--not always fun--but trial & error, lots of error lol.
With springs plus air caps you'd probably only need 5--10 psi guessing.
Think no springs i used about 35psi.
Was nearly 50 years ago.

Damper rod forks are in general not that effective. They tend to be too hard in relation to low speed damping and too soft for high speed.

They can be improved enormously by fitting springs specific to rider weight, and emulators, which work more along the lines of cartridge forks.

That's quite involved, though, and can be costly if springs need to be specially wound.

First thing to try, is added preload to the fork springs, change the oil, and experiment with different grades and amounts. That might be all thats needed.

In response to MarkT: 10 weight fork oil - 175cc in the 360, 130cc in the 175. I was just looking to see if there was spring upgrade. I realize these are not competition bikes, but I would like some damping without bottoming out. Probably just worn out.