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  • XJ650 maxim (US model) popping and backfiring/ rich on cyl 4

    From brandon rendon@21:1/5 to All on Mon Jun 15 07:36:29 2020
    so i got this bike and it would start but would not move (tranny was broke) so i got it home and pulled the motor off the bike and found 2 shift forks, a 1/2 of a gear, and lots of teeth in the oil pan... no problem ordered a new tranny gear set and
    reassembled ran great...

    few months down the road, 1 carb started leaking (as old carbs do) and i figured it was nigh time the carbs be rebuilt/new air filter. did all that, did a wet set for the carb floats and at idle its fine, but as im riding it backfires hard and spits a 6"-
    8" flame out the right side (carb 3 and 4) tail pipe.

    that being said, it was backfiring on both sides before i did a carb sync and set the pilot screw (using a colortune) and now they all burn the proper color however... cyl 4 fouls up almost immediately with black dry soot, whilst all the others stay a
    nice redish brown consistently. at first i thought ok its just a bad plug, i have replaced the plug with 4 different plugs and same result. i figured maybe its the coil (which it shouldn't be as they are brand new dyna coils) so i flipped plug 1 and 4
    with each other to see if the foul chased the plug and it did not... i do not have a ton of experience i learn by doing and have only been wrenching on bikes about 2 years... so now i turn to you guys as i have exhausted my knowledge on troubleshooting
    this issue

    oh yea and it has 1.5" straight pipes as the P/O dumped the bike and broke 1 muffler and decided to cut the other muffler off, we lefft the crossover H Pipe on there so i was able to clean that up and weld in some 1.5" exhaust tubing to it until i can
    find some slips that fit it then i can cut the tubing to the length i need.

    oh yea... also i did just shim the valves like 20 miles ago, if that. it has a k&n air stock fit filter (reusable and new) and im using bp7es plugs (factory recommended plug)

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  • From Robert Roland@21:1/5 to [email protected] on Mon Jun 15 19:06:02 2020
    On Mon, 15 Jun 2020 07:36:29 -0700 (PDT), brandon rendon <[email protected]> wrote:

    fouls up almost immediately with black dry soot

    Black soot normally indicates a rich mixture, which indicates a carb
    problem.

    Check that the float has not sunk (punctured). Take the float out and
    shake it. If something sloshes about inside, it's sunk.

    Check that the float needle seals properly.

    Check float fuel level.
    --
    RoRo

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  • From brandon rendon@21:1/5 to Robert Roland on Mon Jun 15 21:54:35 2020
    On Monday, June 15, 2020 at 5:06:04 PM UTC, Robert Roland wrote:
    On Mon, 15 Jun 2020 07:36:29 -0700 (PDT), brandon rendon <[email protected]> wrote:

    fouls up almost immediately with black dry soot

    Black soot normally indicates a rich mixture, which indicates a carb
    problem.

    Check that the float has not sunk (punctured). Take the float out and
    shake it. If something sloshes about inside, it's sunk.

    Check that the float needle seals properly.

    Check float fuel level.
    --
    RoRo

    i will check and see if its sunk, but i just rebuilt the carbs and did a wet set of the float level.

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