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1982 Yamaha Seca 400 dohc idle issue

Discussion in 'The Garage' started by MoMo, Jun 10, 2019.

  1. MoMo

    MoMo Ride Like You Are Invisible

    Having problem getting my 1982 Seca 400 dohc to idle properly. Inside of gas tank was a mess so I cleaned it with prep and etch but it rusted back up again so I plan to do it again and then seal with RedKote.
    That led to having to pull the Mikuni carbs. Completely disassembled and ultra sonic cleaned the bodies as well as jets, emulsifier tubes, floats, seats and needles. Reassembled, installed on the bike using a remote tank for fuel supply but the sucker will not idle. Idle screw turned all the way down but no go.. I have been unable to find carb specs peculiar to the dohc Seca.

    Actual question is does anyone know float level setting and air screw turns out for the 400 dohc? or is it the same as the sohc 32mm and 1 1/2 turns out?

    Appreciate any help and advice, Larry
     
  2. xschris

    xschris a lifestyle not a trend Top Contributor

    Plastic floats are 22mm brass 26. I would also start with 3 turns out for the pilot mix screws. Any mods to the bike would also affect tuning issues.
     
    buztabuzt likes this.
  3. MoMo

    MoMo Ride Like You Are Invisible

    Thank you for the information. I've been so busy with work and a house renovation that I have not been on the computer for days. Will pull the carbs again( for the fourth or fifth time) and check float level. Mine are plastic so 22mm will be the target.

    Hard to imagine carbs could still be dirty but I might ultrasonic clean again. Will post results. Thanks again....Larry
     
  4. MoMo

    MoMo Ride Like You Are Invisible

    buztabuzt, that link you posted mentioned a plug over the pilot jet. Mine never had one and did run fine until the gas tank crap clogged up the carbs, I assume that pertains to the sohc 400? ….Larry
     
  5. SoulMan

    SoulMan XS400 Addict

    I don't know if all pilot jets have plugs but you might post pictures of your carbs. I know xschris saw that mine was not for a 1980 as it should have been and was actually the model for a 1979. I don't know if that will make any difference but can't hurt.
     
  6. MoMo

    MoMo Ride Like You Are Invisible

    will post photos when I get a chance to pull carbs. May not be for a couple days, still involved with work and a home reno and plan to go look at an Aprilia Shiver at the local Italian bike shop---Guzzis, Vespa, Piaggio and Aprilia. thanks again...Larry.
     
  7. xschris

    xschris a lifestyle not a trend Top Contributor

    I don't believe the dohc bikes used a pilot jet plug.
     
  8. MoMo

    MoMo Ride Like You Are Invisible

    Thanks for that fiche chris. The fiche from another site was mislabeled and useless....Larry
     
  9. MoMo

    MoMo Ride Like You Are Invisible

    no update, still working on a major house reno. Hope to get to the Yammie next week. Eliminated the Aprilia and MT-09(looks too much like a transformer bike but it sure is tempting though) most likely purchase is a Guzzi V9 Roamer. Larry
     
  10. MoMo

    MoMo Ride Like You Are Invisible

    House repair turned ugly. Beam for rear porch completely rotted. However, I was able to pull carbs off the Seca. Even though carbs were ultrasonically cleaned there was a piece of crud blocking left carb pilot. Years ago(early 70's) when I started wrenching one of the older mechanics told me a trick for setting float levels that seems to work if you cannot find float info. That is, make the float arm parallel with the carb body. I had done that, when I took the carbs apart this time the level was 22mm. However, air screws had been set at 1 3/4. Rectified that, put carbs back on, started up with a remote tank. Bike idles just fine now, but I still need more work on inside of tank before I am able to ride it. If anyone has a clean interior tank, I would be interested. Color would not matter as I painted my bike the old, traditional Yamaha yellow with black and white accents. Will post again if I am ever able to get tank useable. Thanks all....Larry
     

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