I have just made my spacer and am keen to fit my new 2.5 slide with spacer - question, you say increase the pilot jet size considerably  - to what size approximately, I need to buy some so that I can test it!

Thanks

I'm running 2.5 slide with 60 pilot and air screw out 1 turn. Decent results. 1976 DT400C. Sleeper pipe too and lightly oiled oem air filter.

Wow - you really do need to up size the Pilot Jet!

I'll order a selection - thanks

Yamaha went to an 80 pilot on the 77 DT400...  very similar engine.  I believe the monoshock DT400 came with a 2.5 slide as well.  So it sounds like Pedalcrazy and you guys are on the right track. 

Just so I'm understanding the 2.5 slide, that goes into the stock carb? 

Hi all,
Please keep us all updated with progress/results. See post #15 - I have a 2.5 slide and a spacer on my twinshock 400, but my engine is in bits at the moment (just got it rebored).
My bike is totally standard (apart from the rebore, Rex ignition conversion and the new slide).
If you can cure the twinshock 400 'shunting' (or whatever word you want to use), you are better than Yamaha!
I think the 2.5 slide must be the way forward because that is what Yamaha used on the later monoshock 400's
Discuss......

I have my 2.5 slide with spacer and a selection of larger pilot jets.
As soon as the weather improves I will fit and test and let you know how I get on.........
Hopefully this week.

I recently finished a rebuild of a 76 DT400. I had a very difficult time with surging. I added a new Mikuni carb and installed factory stock jet sizes. This was just after me thinking it would never run nice and many jet configurations including starting to research a different cut away. I decided to inspect the reeds given they where about the only thing I did not replace, they still looked fine. While bolting the reed cage to the cylinder I installed the gasket. I then realized that there is no gasket between the intake manifold and the reed cage. There is a molded piece of rubber that should act as a gasket on the intake manifold to reed cage connection located on the intake manifold. Mine leaked. I added the same gasket at the reed cage to cylinder on the intake to reed cage connection. Bike starts like a 125 even when hot, no surging. I didn't think I had an air leak, I had an air leak. Still have not tried to set up the original carb for 100% proof, it runs to good to take a apart again. Down side is I'm running a pod, net summer I'll spend a day and try.

Hi - that is all good news. Is your new mikuni carb a brand new item? NOS? Thanks…

Yes, Brand new. Not terribly expensive. It was ordered with a nipple to except the oil feed. I had to change the jets to factory specs, just did this to have a starting point, they worked. Problems: Oil nipple is on the opposite side of the carb, you need a longer oil line, I use clear. The carb inlet is a bigger diameter than stock, very difficult to get connected to the air box.