1978 XS400 Carb Slide questions

[bensonj]

Inside the top of the carbs there is the diaphragm and the slide and spring and needle. My question is about the little plate that the large spring sits on. I am re assembling the carbs, and it looks to me like if this plate isnt floating off the bottom of that side, then no fuel is getting into where the little spring is and the needle. I noticed on the two screws that hold this plate down, there are two little dimples on the head, no doubt to be used for keeping track of where it is. Can anybody help me with this? I just feel like if I secure it fully, it will restrict fuel to the needle.

 

[xschris]

That setup is for a 80-82 xs400 carb slide. Gas should not be up inside the slide itself. When vacuum pulls the slide up, the jet needle rises also letting gas come out of the needle jet. Post pics of the type of carbs you have.

 

[bensonj]

 

[NewHavenMike]

That whole area of the carb should be dry, and clean. That needle setting looks to be a little high also. It should be on the middle groove but it could be different for your particular model.

 

[xschris]

What needle do you have? Most 80-82 sohc carbs have a one clip needle (5GZ9).

 

[bensonj]

That whole area of the carb should be dry, and clean. That needle setting looks to be a little high also. It should be on the middle groove but it could be different for your particular model.

I have the needle set that way based on what a stage 3 carb rebuild kit from Sigma 6 jet kits. Ive been having a lot of trouble getting this bike to run right and hopefully once I am done with this rebuild, everything will be ok and the bike will function properly.

So what you are saying is that, having that plate with the two screws, screwed tight, this will have no affect on how the carb functions?

 

[bensonj]

What needle do you have? Most 80-82 sohc carbs have a one clip needle (5GZ9).

The bike is a 78. Maybe its possible somebody has put different carbs on? I have no clue what needle it is honestly.

 

[NewHavenMike]

Oh man I just looked that kit up. Drill bits?!?! lol no thanks on all of that..

Maybe Im crazy, but there is no such thing as a stage 1, 2 or 3, or 7.. These bikes are all mechanical and when I think of staged tuning, the only thing that comes to mind is new modern computerized cars with turbos and flashed and chips...

Mechanical bikes are very sensitive to any modification, that includes any imperfection like an exhaust leak or carbs not being synced. I know the xs400s came slightly lean from the factory too. Whatever a stage 3 is, Im almost positive you cant just go to a stage 3 while being completely stock elsewhere and not having all the maintenance in perfect condition.

When you tune, you need to do one thing at a time, especially if you havent done it before, dont make drastic changes like how you skipped a needle setting. You tuned the carbs to run rich so thats not a bad thing, but too much fuel is a bad thing. Too lean can be a problem.

It also helps to know what youve done to the bike engine wise and what your carbs are set with. Jets, idle jet, mix screw, filters, exhaust, plugs, timing etc..

 

[Super_wizard]

Hi,
I have the exact same carb and needle setup in my ‘82 xs400, also clip in the same groove as you.
The carb is standard in a Yamaha xs400 SE, mikuni BS34 and my bike runs great with it.
All the rest of my bike is original, airbox, exhaust, cams... exept the side-car...lol
When you look inside de slide with needle installed and the 2 screws in place, there is one hole still open. That hole should be on the engine side of the carb when you install the slide in the carb ! Don’t forget this, very important !
O, i did have to replace the diaphragms with some jbm diaphragms, saves a big buck over the originals.
Carb synced made a big difference for me, did it myself with some clear tubing and a little gearbox oil.

Good luck with yours !

Gino