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Won’t start when hot

Discussion in 'XJ Technical Chat' started by Zack Lescowitch, Aug 10, 2019.

  1. Zack Lescowitch

    Zack Lescowitch Member

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    Hey everyone,

    I have a 1985 XJ 700 Maxim X that I’ve been working on. I finally got it running but once it ran for about 5-10 minutes it died out and won’t restart. If I try again once the engine is cold it starts on the first crank.

    Things to note:

    It started from a cold start and idled around 1000-1500 rpms which I consider normal. After about 2-3 minutes it picked up to 2000-2500 rpms and stayed there for about 5 more minutes before returning to regular idle and quickly dying out afterwards.

    I immediately checked spark to see if the coils were the issue. I had plenty of spark.

    I believe it to be a fuel issue. I have fuel in the bowls and I turned the valve to prime and still couldn’t get it to fire.

    My idea is that it’s getting too hot and cooking the fuel before it reaches the cylinders. Thoughts?
     
  2. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Have the valve clearances been checked?
     
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  3. Toomanybikes

    Toomanybikes Well-Known Member

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    Hot vs cold compression test.
     
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  4. Timbox

    Timbox Well-Known Member

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    Zach,
    Can you fill us in on what you have done to the bike so far? What shape did you find it in, band find or sitting in the Preveuse Owners (PO) shed? The more info we get on what you have done to the bike will help us help you.

    If the bike was setting for a few yrs you will need to pull the carbs and go through them, it is just the nature of having a carb motorcycle. Have you looked down inside the gas tank? Clean or rusty or the gas smells bad? Did the PO have a inline fuel filter you can see? If so is gas flowing through it when you turn the engine over?

    Have you pulled the plugs and taken a look to see what color they are? Shine a light down to look at each piston and see if they are clean or full of carbon?

    As k-moe states above, the valves need to be looked at to make sure each cylinder is getting the best compression it can. Doing the "X" valves is interesting but can be done. It will be costly depending how many of the valves are out of spec. Those little pencil erasure type shims fun.
     
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  5. Zack Lescowitch

    Zack Lescowitch Member

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    So I just check compression.

    Cold compression starting at cylinder 1 and working my way across: 60,55,15,65 psi

    Hot compression after it shut off after running about 10 minutes: 60,70,50,60 psi
     
  6. Zack Lescowitch

    Zack Lescowitch Member

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    I bought the bike from a guy who said it lost spark after getting caught in the rain. What I found was a broken wire within the harness which was weird but an easy fix. After getting it running I noticed the issue I’m having. The tank was clean and since it starts and idles fine when cold I assumed the carbs were fine. My original thought was that it wasn’t pulling enough fuel at low rpms because the boots between the carbs and air box were in rough shape. I replaced those and figured it would be able to pull enough vacuum and run smoothly on the low end. But after I got it back together I let it idle while I cleaned up my tools and that’s when the issue started again.
     
  7. cds1984

    cds1984 Active Member

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    +1 on the plug colour.
    If the mix is super rich it may be akin to the fuel enrichment circuit being open.
     
  8. Zack Lescowitch

    Zack Lescowitch Member

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    Here’s two of the plugs, the other two are similar. Keep in mind they’re new so they might not be as dirty as the would normally be.
     

    Attached Files:

  9. Zack Lescowitch

    Zack Lescowitch Member

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    To address your other questions:

    The bike is in decent condition, some cosmetic issues but no fluid leaks, looks pretty clean, 22,000 miles on it.

    The PO threw parts at it I think when he tried to fix the spark issue. It has new plugs, plug wires, and coils.

    No in-line filter for the fuel.

    I’ll try to check the valve clearances this afternoon.
     
  10. immy

    immy New Member

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    I have a similar issue, my 85 xj700 always cold starts no issue but if I shut off to fill up the tank it sometimes doesn't want to start again for a minute or two. Cranking sounds a little dry to me, maybe a fuel delivery issue?
     
  11. Zack Lescowitch

    Zack Lescowitch Member

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    Uhh so how do I fit a feeler gauge under the cam? There’s next to no room in there. Especially with the engine on the bike.
     
  12. mlew

    mlew Well-Known Member

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    Those numbers are way too low. They are less that half of what they should be.
    Did you open the throttle when testing? Either that or the valves are not closing.
     
  13. Zack Lescowitch

    Zack Lescowitch Member

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    Didn’t touch the throttle. I guess the valves aren’t closing.
     
  14. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    You need angled, narrow profile feeler gauges, or you can bend a set of standard gauges.

    At 22,000 miles the valves might still be in spec, but should be checked anyway.

    The very low compression you're seing might be stuck rings, or more likely due to a faulty gauge.
     
  15. Toomanybikes

    Toomanybikes Well-Known Member

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    Compression test:
    Adjust valves
    Throttle wide open
    Air filter out
     
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  16. Zack Lescowitch

    Zack Lescowitch Member

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    Ok, I’ll have to retry the compression test. I wasn’t aware of those details. However I’m not too convinced that it’ll make my compression jump to 100 or so psi which I assume is normal compression.

    My job has me away from home for the week and my schedule is going to get a little busy soon, but I’ll keep you updated as I move forward.

    Thanks everyone!
     
  17. tabaka45

    tabaka45 Well-Known Member

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    While you are at it, check the voltage at idle--it should be approx 12.5 volts. My XJ700 would sometimes be hard to re-start and it turned out that I was not getting enough voltage to crank the engine and fire the plugs. I was getting only about 11.2 volts at idle and less than 13 volts at about 3000 rpm. XJ550H suggested that I check my voltage, which I would have never thought of. I keep my bike on a battery tender, so it tended to start easily the first time and usually if it was off only for a minute or two for a gas stop. I replaced the brushes and now have 12.5 volts at idle and about 14 volts at 3000 rpm. The bike starts much easier and the restart problem has disappeared.
     
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  18. Zack Lescowitch

    Zack Lescowitch Member

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  19. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    That's
    basically the process, but there are several model-specific details mentioned in the article that are different for the X.

    This thread should do ya.
    maxim-x liquid cooled valve adjusment with pics.
     
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  20. Zack Lescowitch

    Zack Lescowitch Member

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    I appreciate that. So the sprockets can’t stay on the cam shaft for removal?
     

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