Im not sure on how much performance you want to gain, I can do lots to improve that and too much to list here . But one of the best mods for you $$ is to install a UFO in your slide . If you are interested getting serious give me a call 702-858-9177

Rich

I have a UFO in my old TAT bike!

What improvements does the UFO provide over the stock slide?

I’ll let Racerclam explain it, but here is the technical explanation:

thunderproducts.com/product/u-f-o-ultimate-flow-optimizer/

THe UFO provides much better response as well as over all performance , by eliminating the open area at the bottom of the slide which causes turbulence and a huge flow hinderence . The off idle and just above has a much better signal to the needle jet which actually causes fuel to be pulled through it earlier than normal , overlaping the pilot jet which requires a much smalle pilot jet . The UFO causes a round slide carb to out flow an equal size flat slide up to13/16 throttle opening . Couple The UFO with venturi dividers and you will have a awsome carb with linear smoother , stronger performance

Thank you for the input. How does the ufo and dividers install?

THe dividers are hand fabricated by me per carb. I can also install the UFO give me a call if your interested 702-858-9177

Rich

From what I have read here and elsewhere on the internet if there is one thing on the 77/78 Dt400 to do - is address the intake port. All other stuff secondary. Just file the bottom of the port down or use a dremmel. A medium half round file works good. Make sure to deburr the port edge with some sand paper. It is not difficult at all. 30 minutes and your done. I like sanding rolls with a dremmel better than carbide because carbide can wreck a cylinder in less than a blink of the eye. It may be a little goes along ways. I would reccomend with 1/8 inch or so to start. I don't have enough experience to tell you the best number. I lowered my port 3 or 4mm. The 75 Dt 400 has the piston skirt cut away seperating the boost port from the intake. When the bottom of the skirt passes by the top of the intake port window the port opens up to fill the crankcase further through the boost port. The 77/78 have the boost port seperate so the intake is port is smaller. That may be why the 75 is reported to have 3 more ponies than the 78. To get more flow you can lower the intake port floor or raise the windows in the piston, or drill boyesen ports from the intake to the secondary transfers. I reccomend the boyesens because they don't depend on what the piston is doing at any particular moment to fill the crankcase with fuel and air. They also have good flow right at the get go as the piston just starts to rise from bdc. I made mine equivalent of maybe a 11 to 13mm hole ovalized. The great thing with the boyesens is that they can be filled back in easily.

LOwering the intake port as much as possible without sacrificing cylinder spigot strength is a big plus . Ther is no magic number it ony helps . Boysen ports are ok and do help but I go beyond by making a case port , that directly connects the intake to the crank case . Bothe together and the bigger the boysen ports the better . This cylinder is a Cr 25 Honda . I do practically all vintage cylinder this way for bikes and sleds . As far as the pistin goes the only reason the rear of it is necessary on a Reed engine is to support the piston . Holes are good but not to the point of weakening the piston .

Rich

Rich

Beautiful work. Yah I did both the boyesens and dropped my intake, plus the 3 Rd window in the piston. I figure the piston window plus the boyesens in combination fits non porters like me. I have read the combo does wonders but not to the extent that the level you can take it too. I appreciate all the input too so keep her coming.