I'm interested in increasing my throttle action reducing the amount of travel required to reach full travel. This is on a stock '78 DT400 E and I am wondering if there is an old trick to modify a throttle to get it to respond faster. I'm hoping an old MX guy has a way to do it from back in the day when you couldn't buy it you had to make it. I don't want to replace the original housing and loose the switches etc. if I can avoid it. Any Ideas???
Thanks,
Art J.

Can't see anyway sorry without replacement. The twist grip tube on yours is unlikely to have any room to fit a bigger tube-cable spool thingy.
Just coming up with silly ideas, my 490 came with an easy pull clutch thingy. That's actually the reverse of what you're asking but could something like that work if you reverse configured it!!. Think i'd give up & just slide the switch part down the handlebar minus the tube & then buy a quick action throttle. I bought one with cable for very little of ebay a while back.

You might be able to find a throttle tube with a larger pulley end that fits into the stock housing. Motion Pro has a lot of tubes.

What I did many years ago was took a piece of ABS pipe cut just wide enough to fit in the housing. Then I cut a section out of it, soaked it in ABS primer to soften.... and wrapped it over the stock pulley. Then epoxied the sleeve over the stock pulley.

The sketchy part was I took a saw blade and carefully grooved the ABS for about a half inch to cut an angle slot to transition the cable to the outside of the ABS. I did not groove all the way around like stock. I did this before gluing the sleeve in place.

I was a little worried cable might slide off the new ABS pulley... which is why I made that piece close to the width of the housing. Still worried me a little though.

But before that happened, I broke the throttle cable. One thing I didn't think of is that the stock throttle has an internal stop and with the new quick action I was twisting too hard at full throttle and stressing the cable.

At that point I bought a Gunnar gasser... this was on a premix dirt bike so no switches or cable splitter to worry about. I just had more time than money as a kid so tried to make as much stuff as I could in the garage... thinking about it... I don't think I had epoxy... I think I used 3M yellow weatherstrip adhesive to glue the sleeve over the stock pulley.... we used to call it "gorilla snot"... really strong glue at the time.

Found a video of what i meant. drag it to about 1.02 & study how it works. Now, if you ran it in reverse with the twist grip into the lower one & the carb into the top one you'd have increase lift for the twistgrip. Then again, i never thought--probably not enough movement for total slide travel. Could be though if it started from totally to the right side.

At my age I'd like to find a throttle that slows down the response.

have to be careful... best Gunnar Gassers are still made in Sweden... tons of knockoffs out there and some are prone to failure.

Motion Pro makes a good one too.