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Discussion in 'The Garage' started by Scotty4, Aug 15, 2020.

  1. Scotty4

    Scotty4 XS400 Member

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    Pulled the caps and checked compression so far. 175 on both cylinders. Putting together stuff for a manometer currently.
     
  2. xschris

    xschris a lifestyle not a trend Top Contributor

    That's very high compression. These should be around 150-160. You may have a build up of oil and carbon. After you put some long rides on it that should clear out.
     
    Scotty4 likes this.
  3. Scotty4

    Scotty4 XS400 Member

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    Thanks for confirming my thought of it being high. The synch was off at idle but dinner arrived and drinks. Should I adjust pilot then synch, drink, repeat?
     
  4. xschris

    xschris a lifestyle not a trend Top Contributor

    Only sync at idle. Which is 1200rpm. Do it Again when the bike is at full temp. Yes adjust mix.
     
    Scotty4 likes this.
  5. amc49

    amc49 XS400 Addict

    Engine has only 500 miles on it, that compression not too high to me, about right for new engine. I look for 170 on my Honda fours and they have less advertised compression than these IIRC. The lower compression will be after say 5K miles and the new wears off to stabilize and hold. Could even be gauge error easily.

    Don't be surprised if sync does nothing for the carb issue............
     
    Scotty4 likes this.
  6. Scotty4

    Scotty4 XS400 Member

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    Pulled the carbs again to bench sync. Just adjusted both flaps halfway over the first hole and verified they were close with a feeler. Set the pilot screws 2-1/2 turns out. Put everything back in and hooked my manometer up. Only needed half a turn on the sync screw and she idled better and can redline. Took it for a spin and I'm in love.

    Now here's where its at: tough to start when warm and it takes off well but anything over maybe half throttle while riding just causes more noise with no rpm increase. Revved it hard and cut it off to coast into the driveway and check the plugs.

    Clutch side looks clean. Brake side looks tannish. Only went about 6 miles doing 50.
     

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  7. xschris

    xschris a lifestyle not a trend Top Contributor

    The brake one looks good if you had driven 100 miles or more. So the bike won't pull over 5k rpm's in any gear? I would not pull the plugs if the motor is hot. The soft aluminum head treads can get damaged. Are you running non-resistor caps with those resistor iridium plugs?
    Have you removed the emulsion tubes in the carbs to be cleaned? It's also know as needle jets. These are for 1/4 to 3/4 or so of your rpm range. All circuits, pilots and mains, overlap and have effects on rpm ranges. But that is more pronounced for those.
     
    Last edited: Aug 31, 2020
  8. Scotty4

    Scotty4 XS400 Member

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    It will slowly get to higher rpms but if I twist full throttle it seems to not go any higher. So maybe it doesn't? I'd have to ride it again. If I hold 1/4 throttle it'll gain speed easily.

    Not sure what you mean about the plugs? I bought the pair recommended on here.
     
  9. xschris

    xschris a lifestyle not a trend Top Contributor

    Your plug caps need to be checked for ohms. With your plugs they need to be non-resistor. CV type carbs will not act like a direct pull slide. It's more of a gradual increase. A well tuned bike/carbs will act very snappy. Yours still may need some work. When you check your needle jets you should check the needles and see what notch they are on. The forth from the top is what the 78-2E calls for.
     
    Scotty4 likes this.
  10. amc49

    amc49 XS400 Addict

    My bad........
     
    Last edited: Aug 31, 2020
    Scotty4 likes this.
  11. Scotty4

    Scotty4 XS400 Member

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    Thanks agaun for the help guys. I'll pull them off again and check everything over. Was really nice to have it running again. My mom was the last one to ride it with my grandfather so it was a nice moment for her to hear it and watch me ride around today.
     
    motoTrooper and xschris like this.
  12. motoTrooper

    motoTrooper XS400 Addict

    Nice looking old stocker, from the pics it looked like the right cylinder ran very lean at some point from the blue color of the pipe. Sounds like your getting well familiarized though and bringing back some good memories.
     
    Scotty4 likes this.
  13. Scotty4

    Scotty4 XS400 Member

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    Thanks! I'm coming around to it slowly. When I was little, I always thought it was big and going to be hard to ride. Now that I have riden other bikes daily for the last 5 years, it feels just as good as the newer ones. Didn't think it would sound as good either!
     
    xschris likes this.
  14. Scotty4

    Scotty4 XS400 Member

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    @xschris just checked the coil resistance. Left side plug wire to both orange and red/w wires is 19.02k ohms and the right side is 18.37k ohms for both wires. Pulling the carbs to check the needle jet setting.
     
  15. xschris

    xschris a lifestyle not a trend Top Contributor

    Did you check them without the caps on thE wires? Looks like you still have the stock resistor caps still. You need to replace them with non-resistor type.
     
  16. Scotty4

    Scotty4 XS400 Member

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    That is for these sparks correct? If I go back to stock plugs it should be ok?

    Also looks like my petcock is leaking slightly and flooding stuff. Good thing I have more oil.
     
    Last edited: Sep 6, 2020
  17. xschris

    xschris a lifestyle not a trend Top Contributor

    I would just check the caps for ohms also. The stock ones where between 7-9k ohms. If they are more than that I would get some standard 5k ones. But that is for the non-resistor plugs if you go back to them.
     
  18. amc49

    amc49 XS400 Addict

    Your coils should be reading roughly 12K (+20% error on 9.5K ohm spec) max, you have too much resistance there. The plug caps often do it and dump any resistor plugs too, marked with an 'R' somewhere in the number on plug. No resistance at all in the plug wire itself from coil to plug, they need to be less than 5K per 12 inches of length. I use zero and add it slowly back by simply opening the plug gap up a bit to make up for it, say start at .005" wider. Are the plug wires removeable on that type coil? If so check them as well if the wires are not OEM colored; sometimes people stick resistor wire in there too for 3 resistances in the secondary and just crazy. If the plug wires are molded or glued into coils you may not have to worry about them. Although the rare person like me has changed them by carefully drilling the coils out to change to new plug wires.
     
  19. xschris

    xschris a lifestyle not a trend Top Contributor

    You also need to check your primary resistance which should be 4 ohms +- 10% at 68 F
     
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  20. amc49

    amc49 XS400 Addict

    If you have the oldschool plug ends/caps that screw in from the plug end then you often can unscrew the end and pull the resistor out to replace it with a like length piece of say bolt cut to EXACT length and slip the bolt piece back in to replace the resistor and screw the end back in to hold it in place. The resistor looks like a small glass fuse. Done like that you have a zero reading cap, the resistance is gone. Some caps though have the resistor molded in and you cannot remove it.
     
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