1. Hello Guest. You have limited privileges and you can't "SEARCH" the forums. Please "Log In" or "Sign Up" for additional functionality. Click HERE to proceed.

Rev and return to idle problem

Discussion in 'XJ Technical Chat' started by Colintosh, Oct 17, 2014.

  1. bigfitz52

    bigfitz52 Well-Known Member Premium Member

    Messages:
    21,283
    Likes Received:
    415
    Trophy Points:
    83
    Location:
    Rural SE Michigan 60 miles N of Motown
    ONLY MAYBE.

    However, if say, 6 of the eight valves are at zero clearance plus the carbs haven't been properly serviced yet IT AIN'T GONNA RUN.

    And once the carbs are all sparkly clean, float levels all wet-set and bench sync'ed, if the bike still has a handful of tight valves it probably won't want to start. And will be all but impossible to tune.

    There is a reason that valve clearances are the very first maintenance procedure in the service manual.
     
  2. Polock

    Polock Well-Known Member

    Messages:
    9,751
    Likes Received:
    2,093
    Trophy Points:
    113
    Location:
    Beaver Falls, PA
    service manual, factory service manual, for dealers, follow the money. if i take a bike to a dealer and say it's running a little rough.......adjust the valves first $$$. no matter what, it's always adjust the valves. i might have a tank full of water....adjust the valves first. this insures that nobody gets out cheap. if you say tune it up, that's adjust the valves. if you say make it run, not so much.
    if it ran ok when you parked it, it will run again without touching the valves
    i'am done
     
  3. FtUp

    FtUp Well-Known Member

    Messages:
    1,309
    Likes Received:
    94
    Trophy Points:
    48
    Location:
    pacific northwest
    wet setting the floats after rebuild is very important. use a left hand twist drill bit to remove the old screws ( al little heat helps them break loose) and replace them with the hex head ones from len.

    CN
     
  4. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

    Messages:
    14,626
    Likes Received:
    5,008
    Trophy Points:
    113
    Location:
    near utica, new york
    Well, yeah......if all or almost all of the valves are at zero clearance, of course---but from what I could tell from the discussion, we weren't talking about almost every valve being SO far out of spec that there's absolutely no clearance left. I just find it amusing that sometimes the comment along the lines of "if you have a valve out of spec, your bike can't run" comes along. There's more to it than that. And with that, I simply mean that even when a valve is out of spec, there can still be plenty of clearance that will still allow for fuel to enter, compress, combust, create power, etc..... Of course, it wont be optimum, but with the variables that are inherent in the bikes, there is enough give-and-take that will allow for some lattitude.

    and I'll throw some other fuel on the fire, too, while I'm at it.

    I have NEVER done a wet-set on the floats. I carefully set them and that's it. I haven't had a single bike that has had any running issues from having done it this way. I'm not saying it's the right way, but I'm not saying it's the only way, either............. But I will also always suggest that it be done.

    Just like with fuseboxes......I fully and wholeheartedly think the blade-fuse upgrades are awesome. AND........of course, having said that-----every bike that I have on the road is still running on the original factory fusebox.

    dave
     
  5. bigfitz52

    bigfitz52 Well-Known Member Premium Member

    Messages:
    21,283
    Likes Received:
    415
    Trophy Points:
    83
    Location:
    Rural SE Michigan 60 miles N of Motown
    I'm running (rebuilt) original fuseboxes too. And also recommend the upgrade to anyone so inclined.

    You missed my point on valve clearances. Of course, one or two or even six valves slightly out of spec won't keep a motor from running. When they get tight enough they affect valve timing and that cylinder starts to lose compression and will then affect how the motor runs. Completely ignore an XJ long enough and the day WILL eventually come when it won't make enough compression to run due to all of the valves being tight and half of them dead tight.

    My point was IF YOU HAVEN'T EVEN CHECKED THEM then you have absolutely no idea what you're dealing with; you might very well have a motor that was neglected until it would no longer run. If you get your hands on an old bike with no first-hand knowledge of its history the first prudent step is a compression test. Due to the design of these motors, a few way-too-tight valves can seriously skew said compression test. So if you're serious about the recommissioning, step one is to get the valves in spec and step two is to do compression tests. Then and only then do you know for sure what you're dealing with. To try to adjust or tune carbs on a bike with unknown valve clearances is a complete waste of time. Sure, it might run. Or not. But if you're truly serious about getting it running right, then that's where you start.

    Wet-setting is more precise than dry-setting can ever hope to be. Please keep suggesting that it should be done. It's also a very good way to catch other float related inconsistencies or leaky valve seat seals, fuel rail issues, etc.
     
  6. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

    Messages:
    14,626
    Likes Received:
    5,008
    Trophy Points:
    113
    Location:
    near utica, new york
    and THAT is exactly my point :)
     

Share This Page