Cleaning 1977 RD400 carbs

[RD400]

Today I removed both carbs from the bike and completely dissassembled them. They were soaked for 1 hour in Gunk, 1 gallon carb cleaner (the pail that comes with the parts tray) and then blew out the parts.

I found some garbage in the left emulsion tube and that turned out to be the main cause of the bike sputtering at lower rpms.

It runs MUCH better now. Also, checked the timing and points and both were so close to perfect that I only adjusted the right side by .1 mm

STILL doesn't pull like my old RD350 tho. The 350 would have smoked this 400. (It outran every RD400 in town, including the Daytona Special back in the days (1976 - 1980).

[premiumjo]

Great advise. The holes in that tube are so tiny, that any deposits keep it from doing it's job. A note on timing. I was browsing through MotoCarrera's website, and saw that they recommend timing of .070" BTDC as opposed to the original spec of .090". I set my points according to this and it starts with 1/2 a kick hot or cold, and runs strong all the way to redline (well actually to the area near redline which is in my comfort zone ) Also, it's way safer with a 30 year old motor.
rd

[RD400]

Cool. I'll have to check that out. I still don't feel I'm getting peak performance from the 400 but it could just be me. I'm hesitant to move the timing closer to TDC for that reason. However, I do agree with your thinking. It's getting harder to get pistons and stuff.

The carburetor "bug" came back to a lesser degree. It ran perfect for a day then started to blurble just a little since then. Obviously, there's still a bit more junk in there so I'll be taking them out yet again. I added inline fuel filters on both carbs just in case there was trash in the tanks coming down.

Without drilling the little brass stops that close off the passages, you can easily miss junk that's backed up in the tiny canals. I soaked them for an hour but apparently there is junk backed up in there somewhere. I'll bet that when I remove them again, I'll find more junk around the emulsion tubes. The left one was pretty bad.

I also removed the baffles and the performance was not noticeably different so I put them back in.

[wheelman59]

I used one of those carb cleaner cans too. I ended up having lots of problems. I know this sounds crazy, but Scrubbing Bubbles bathroom cleaner and water turns out to be a fantastic way to clean these carbs. A local friend/Yamaha dealer gave me the tip. After you get them good and clean, dry them with shop air and you're ready to go. I have had no problems since using this method. Apparently, the bucket of carb cleaner leaves a residue that does not mix well with 2-stoke oil... but that's just a guess.

[cwnist]

I have RD400 that has been sitting for awhile and I need to redo the carbs but the throttle valve is frozen. Can any one advise me how to free it up so I can remove the top of the carb?

[premiumjo]

I would remove the screws in the sides (phillips head, for checking synch) and squirt shit loads of penetrating oil in. Also, unbolt (if you havent already) the carb and you should be able to get under the slide with something (use something wooden if you can as not to scratch the shit out of everything) and start prying a little. worse comes to worse, you could try using a small drift to punch the needle jet up and use it to force the slide out. Just make sure you have the cap loosened all the way.
RjD