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What am I Missing? (timing?)

Discussion in 'The Garage' started by pulmenti, Nov 5, 2023.

  1. pulmenti

    pulmenti XS400 Member

    It's me again - the bike won't start. Here's a brief summary of everything I've done.

    1982 xs400j Maxim (dohc), bought with carberator issues and revhang, wouldn't rev above 4500 rpm. Cleaned carbs, retested, no change. Rebuilt carbs with original carb parts, some change - no longer running rich. Recleaned carbs and lubricated slides, mostly fixed revhang. Still would not rev. Checked valve clearance, found each shim to be about .1 mm too thin. Ordered new shims, put into bike, rechecked valve clearances, all within the .1 to .15 mm spec, unfortunately messed up here and loosened the intake cam clamps too much, causing the cam chain to tighten and push the cam out of place. put it back in place, reassembled, now will not start. Checked for spark, found faulty plug boots, replaced, spark ok, no change. Fuel / air ok. Checked timing, here's where I may have messed up again.
    Timing was set so that both intake and exhaust cam's dots on the top side of the ends lined up with the arrows on the camshaft clamps when the timing line visible in the viewing window lined up with T.
    Rechecked, still would not start. Checked compression, found 125 on right cylinder and 100 - 110 on left, 130 with oil added.
    What's the next step here? I'm hesitant to believe that compression is the fault, since it at least started before, but where do you think I should go from here?
    Many thanks again,

    Attached Files:

  2. newclind

    newclind XS400 Member

    Isnt the compression suppose to be 140-170psi? I dont know if 82 maxim is different than 80 special.
  3. tstidham

    tstidham XS400 Addict

    While the compression is a bit low on the one cylinder, usually anything over 90 will run. I'd check the ignition timing next.
    CaptChrome likes this.
  4. pulmenti

    pulmenti XS400 Member

    hi, many thanks for replying - yea, I don't think the compression would be an issue to at least START it. This bike has electronic ignition timing, so is it still settable? My understanding was that it was automatic. My cam timing looks good to you? I was having trouble deciphering the book.
  5. pulmenti

    pulmenti XS400 Member

    I'm pretty sure the maxim, seca, and special all share the same DOHC 400, but there could be differences in tuning. The numbers read low to me, too, but at this point I'd be happy if the bike just ran and idled properly, which it (sort of) did before. So something I've done has messed that up; it's about 20 degrees where i am so i'm hesitant to start dissasembling to inspect pistons / rings lmao
  6. newclind

    newclind XS400 Member

    I was having hard time starting for weeks and I found out that 6 turns out of the mixture screw solved my idle problem. My bike is SOHC and my right side has loose muffler so it running little lean on the right and little rich on the left. But, it runs on the first kick and idles perfectly.

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