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REPETE'S XS650B Preservation Carburetor

Discussion in 'The Garage' started by REPETE, Oct 31, 2019.


    REPETE XS650 Enthusiast XS650.com Supporter

    Good Morning!
    2M, I'm hoping I can describe sufficiently.
    The air vent passage is definitely clear. I've blown carb cleaner and air through it and witnessed the exiting. In addition, when I've removed the carb and turn upside down and then back upright gas will flow out of it. When installed, I've run the motor both without a vent rubber tube and now with a vent tube in place. There are no kinks in the vent tube and it's presence or lack of has made no difference. If I missed a key piece please let me know and I'll execute your thought.

    sidenote: I see you're in Fredericksburg. My brother lives in Houston (formerly lived in Katy), Mother lived in Katy, daughter in San Antonio and this XS was "imported" to here in FL from Waco :wink2:

    Last night's homework assignment completed:
    • check pilot & main jet orifices... brass jets present & clean
    • examine mix screw(s)... both good to naked eye note: I failed to bring to work to examine the fine tips under my scope. I'll followup on this.
    • compression check... right cylinder (the one in question) @ 155psi left cylinder (no operating issues) @ 125psi
    Additional info: new development. yesterday afternoon I went to DMV to title & register the bike. In FL you have to present the vehicle if it came from out of state. So, I rode it to the DMV. It's a very short ride (5 mins) and along the way from the right exhaust pipe was burbling, snap, crackle, pop and more burbling. And when I got there and parked the bike was idling at over 2k rpm b/c the right carburetor was somewhat working. Not smoothly, but it was doing something. On return and while slowly going through my neighborhood at slow speed more burbling, snap, crackles and pops. I couldn't check for idle on return to garage b/c there were people there and the bike is somewhat loud. maybe this is a sign of hope?

    TwoManyXS1Bs and gggGary like this.
  2. gggGary

    gggGary Stop that! XS650.com Supporter Top Contributor

    75 uses one choke on the LH carb and a crossover tube to bring rich mix to the RH carb. Everything good there? good tube well sealed both ends. Perhaps block that tube as an experiment, a ball bearing shoved in would do it.

    REPETE XS650 Enthusiast XS650.com Supporter

    I'd say the crossover is good in that I sprayed with starter fluid while bike was running to see if I had an air leak (suck) situation and it's sealed tight.
    I could certainly run through this experiment. It is something worth consideration.

    gggGary likes this.
  4. gggGary

    gggGary Stop that! XS650.com Supporter Top Contributor

    So with the bike running crappy at low RPM for a while, shut down and pull the plug, what does it look like? I'm thinking a massively lean idle??? Your perseverance here is amazing. Props!
    grizld1 likes this.

    REPETE XS650 Enthusiast XS650.com Supporter

    gggGary -
    "I'm thinking a massively lean idle???" -
    My hope is to take the bike for a ride through the neighborhood after work today which would be nothing but slow speed. I can pull it then.
    That'll be 1st item on today's to-do list

    "Your perseverance here is amazing" -
    Thank you, sincerely. Friends, neighbors and family simply consider me nuts :yikes:
    grizld1 and gggGary like this.

    REPETE XS650 Enthusiast XS650.com Supporter

    Figured I'd show y'all what you're helping me with.
    Remember... this is a preservation - not a restoration.


    I haven't put the air boxes/cleaners on yet b/c I want to get it running correctly first. I would never ride w/o filters other than occasional test runs.
    Mailman, Team Junk and GLJ like this.
  7. grizld1

    grizld1 Grumpy old man Top Contributor

    Good looking machine!

    You're here, Pete, so of course you're nuts, but congrats on your patience and ability to do step-by-step troubleshooting instead of hiring a boat to take the B on a one-way cruise. Gremlins can hide but they can't run. You'll catch the rascal.

    Excuse me if you've already eliminated this possibility, but even NGK can produce a bad spark plug. It's rare, but it happens.

    REPETE XS650 Enthusiast XS650.com Supporter

    I've swapped the plugs from side to side more than once. Has made no difference.

  9. 5twins

    5twins XS650 Guru Top Contributor

    Are your spark plug caps new or originals? The originals can (and sometimes do) go bad. Their resistance starts to climb and eventually it starts choking off the spark. Higher RPM operation may push through that added resistance but lower speed running might not.
  10. REPETE

    REPETE XS650 Enthusiast XS650.com Supporter

    5T -
    New plugs, caps, wires and condenser
    The coils are still original.
    Spark on right side not really any different than that on left side.


    EDIT: it was doing this prior to putting all the new ignition components on.
    Last edited: Nov 19, 2019
    grizld1 and gggGary like this.
  11. REPETE

    REPETE XS650 Enthusiast XS650.com Supporter

    additional thoughts from today...
    I printed (and will have spiral bound) a copy of the XS650 Garage Carburetor Guide.
    An advance thank you to the authors who have been helping me here... Grizld1 & 5Twins :bow:
    Two things I picked up on.
    I had said that I sprayed the carb down with starter fluid when the bike was idling.
    Perhaps I should go back and with a spray nozzle spay directly onto the ends of the butterfly shaft. :umm: Apparently there are seals there.
    Also, I installed new (Mikuni) pilot jets (already verified as the proper style) and I matched them to what came out as well as a listing I had found on XS650.com breaking down the various size jets, needles, etc. I think the same info. is on MikesXS.com. Everything matched, so what came out was stock and what went in was stock. But, what are the chances that for some reason my right carb pilot needs to be increased or decreased in size? Or, am I barking up the wrong tree here?
    Leaving work now and I'm goin g to take the bike for a short ride, monitor the symptoms again and then look at the plugs after I get back and let it idle for a bit.
    More to come....

    TwoManyXS1Bs and gggGary like this.
  12. grizld1

    grizld1 Grumpy old man Top Contributor

    I'm an old dog, but gggGary taught me a new trick when he suggested using an unlit propane bottle torch instead of aerosols to detect vacuum leaks. That's a much better and safer method.
    Mailman and gggGary like this.
  13. REPETE

    REPETE XS650 Enthusiast XS650.com Supporter

    Now that is a cool trick!
    I will admit I did have some concerns with the aerosol.
    I’m going to try it. But tonight has slipped away and I’d be disturbing the neighbors if I were to try now. I live in a townhouse community.
    Some new developments though.
    I took the bike for a 10 mile ride.
    When I left all was as I described yesterday - right side burble, crackle & pop.
    By the time I got to about 3 miles, the burble, crackle & popping lessened but the idle was not settling down. Just like when I’ve had air leaks on my two strokes.
    Then, by the time I got about 8 miles in it was running perfectly.
    Smooth idle. Responsive right carburetor. Smooth acceleration from a stop and a pleasure to travel at low speeds (1st & 2nd gear). It was as if it fixed itself.
    I got back to the house. I could tell that right side was still lean by sound of exhaust on deceleration but not even remotely like it had been.
    I put it up on the center stand and “blipped” the right carb (only). Immediate response!!!
    I then removed the left side plug wire and it was idling on the right side only.
    So, I then started going back and forth from side to side killing off a cylinder and adjusting idle speed.
    All was good, and then suddenly right side wouldn’t run solo as it had been.
    But, it still was instantly responsive to its throttle being blipped.
    When done, I pulled the plugs.
    Here they are. The lean one is the right side... the problem side.



    one last observation from tonight. And hopefully not a whole ‘nother can of worms.
    I’ve been suspicious of the motor possibly running hot. But I don’t know what’s normal with these things.
    This is far from scientific but tonight, after my ride and another 10 minutes of idling I turned the motor off at 5:50pm.
    At 7:30 pm the crankcase was still very hot to the touch. Just mentioning.
    Perhaps has to do with the lean condition.
    That’s it for tonight.
    Tomorrow I’ll try the propane or spraying directly at the ends of the “butterfly rod” to check those seals.
    I sense that things have gotten better - but don't know why or how. :umm:

    Last edited: Nov 20, 2019
  14. Tomterrific

    Tomterrific XS650 Junkie

    The last picture on the first page seems to show the slide reversed. I didn't read beyond so pardon if this has been noticed.

  15. REPETE

    REPETE XS650 Enthusiast XS650.com Supporter

    Thank you Tom, but there's no issue there. As you are likely to know the slide can only go in one way if the rubber tab on the "skirt" is aligned with it's corresponding indentation atop the upper carb body. I'm not seeing what you're seeing there. However, that cab has probably been apart and reassembled 1/2 dozen times since that pic was taken.

  16. 5twins

    5twins XS650 Guru Top Contributor

    Am I seeing that plug number right? A B8HS? Even though that was the recommended plug for the older models when they came out, it's common practice now to use BP7ES plugs. The "BP" portion of this plug's designation means it has a projected tip. This sticks down into the combustion chamber better and is supposed to give a slightly better burn. The number 7 is also a step hotter than the 8. While that probably won't be good for your lean running right side, it should clean up the burn on that darker left side.
  17. REPETE

    REPETE XS650 Enthusiast XS650.com Supporter

    Good Day 5T

    You're seeing B8ES
    I have 7's but given the lean condition at this time I'd be afraid to introduce it.
    As far as left cylinder burn... I leaned the mixture screw in by 1/4 turn. It was out 1 full Now at 3/4.
  18. 5twins

    5twins XS650 Guru Top Contributor

    And "BP"7's I hope? Yes, you're probably better off sticking with the 8's until you get this issue sorted, but then BP7's would probably work better for you. As you can see, the center electrode hangs out of the bottom more and is more exposed .....

    Machine likes this.
  19. REPETE

    REPETE XS650 Enthusiast XS650.com Supporter

    "And "BP"7's I hope?"

    Nooo Good Catch!!! I have B7ES
    I won't use those and I'll get the BP's
    Thank you!
  20. 5twins

    5twins XS650 Guru Top Contributor

    They are commonly available at most auto parts stores for not much more than $2 each. I buy them by the 4 pack.

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