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Dead Cylinder but has compression spark and fuel?????

Discussion in 'XJ Technical Chat' started by SM85, Nov 4, 2019.

  1. SM85

    SM85 Member

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    Guys,

    I am stumped on this one, if you become to know me I only ask for help when I am completely jammed up.

    I have a 1983 XJ650k Maxim. Cylinder #3 is not running (Cold), it has 150psi compression, spark (verified spark with a Spark Length Tester at 6mm), and new spark plug that is gapped correctly. The spark plug has fuel on it when I remove it from the cylinder.

    If you cover the #3 Carburetor air collection port, above the intake side of the carburetor, engine RPM will increase. Seems #3 header will pickup some temperature, cylinder seems to be running when covering the #3 carburetor air collection port with finger. I thought I had put the main air jets in backwards, but I checked anyways and I did not. On number 3, I screwed the pilot needle further out to check if increase in fuel would help.

    Thinks I have tried...
    Thought of a lean condition.
    The air boots appear okay, i put an inspection light in the boots and cannot see any light.
    I also ran a rubber hose on the tip of my propane torch, and no rpm increase in that area.

    I have fully disassembled and done the carburetors, carbs were hot tank dipped for cleaning and blew all passages out with brake cleaner and air (paying attention to the 32mm hitachi carb diagrams). Polished slides and verify diaphragm operation. Polished all needles and float seats and unplugged the emulsion tubes. I set the float levels to precisely 3mm for each carburetor and set the Pilot Fuel Screws 3 turns out.

    This is starting to get frustrating. I am obviously missing some small thing.

    Any advise is greatly appreciated.
     
  2. Ryengoth

    Ryengoth Active Member

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    Sounds like it's getting quenched (too rich) and the sync is off between 3 and 4. Did you sync the carbs? Do that first if not or you will be chasing your tail on EGT and mix tuning.
     
  3. SM85

    SM85 Member

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    Thanks for reply! , does it matter that the cylinder isn't running for vacuum sync? I have a vacuum gauge all ready to go.

     
  4. Timbox

    Timbox Well-Known Member

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    Sounds like you are almost there, did you happen to read this https://www.xjbikes.com/forums/threads/in-the-church-of-clean.14692/ That is the correct way to clean the carbs. As far as trying to do a sync without all the carbs and cylinders firing, well just don't. It would be a waist of time.

    I don't know how many CV style carbs you have cleaned, but they are hard to do correctly the first time. It can be done, but most take a few times to get them correct. I have had to pull carbs many times to get them correct before I took the time to do them by way of the "church".

    Get that dead cylinder running before you go any farther. If you have not checked the valve specs that could be causing some issues too. Did you do a bench sync when you had the carbs off? You can get them very close just with that.

    Is your battery new or in really good condition. Lost of us have issues with low or bad batteries that make the bike start hard or lack of good spark.

    Keep at it, if you get that frustrated, just take a brake from the project until you feel you can work on it with a clear mind. Best of luck.
     
    Franz likes this.
  5. Polock

    Polock Well-Known Member

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    no, not at first
    swap the plug with one from a hot cylinder
    3 turns out is about the limit, try going in
     
  6. SM85

    SM85 Member

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    I have jumped the battery with a new excellent commerical HD battery and no difference, then I did the full spark test.

    I have swapped hot plugs in, and I have tried screwing in the pilot fuel inwards as well.

    I followed that Church of Clean writeup and did much other research before starting. But I did not bench sync, would this cause a cylinder not even to idle?

    I am running the engine with #3 vacuum line (The one that runs to the spigot plugged off), and the spigot in prime mode for a gravity feed to fill the bowls. I also am not running the air box yet, would either of these cause an issue?
     
  7. XJ550H

    XJ550H Well-Known Member Premium Member

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    motor should run fine with out air box for testing purposes

    how did you plug off the nipple on 3? test it for a vacuum leak

    also if you have not installed the airbox boots bench sync the carbs

    can you see the slide move up on 3 when opening the throttle?

    you said
    If you cover the #3 Carburetor air collection port, above the intake side of the carburetor, engine RPM will increase.


    have you checked the diaphragm for holes?
     
  8. Timbox

    Timbox Well-Known Member

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    If you can reach them, test the diaphragms by pushing them up and keeping your finger over the oval opening. If it stays up of slowly comes down the diaphragm is working. If it slams down, it has issues. A hole, rear or just not seated when the top went back on.

    I would take some compressed air and blow out that #3 cylinder to make sure it is good and dry. If you have spark on #3 and you said the plug gets wet from fuel, it could just have too much fuel in there to fire???

    Did you do a wet set of the carbs?
     
  9. Ryengoth

    Ryengoth Active Member

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    No, the piston is tied to the crankshaft so it will be creating vaccum if the engine is turning at all. You can even do it with the starter and the plug wires pulled, just to get the initial shaft alignment in the ballpark. You will need to re-tweak at revs based on the book with the engine running.
     
  10. Ryengoth

    Ryengoth Active Member

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    ^^^
    Bench sync is a much better alternative than the starter-crank method since you can see where the butterfly is in relation to the fuel orifices. That's what I used and it worked well for the no-filter initial tune.

    Turn the mix screws in all the way and then out 2.5 turns to start with on all 4. If you have more than 3 full turns you are flooding the cylinder on stock jets.
     
  11. XJ550H

    XJ550H Well-Known Member Premium Member

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    air collection port? thr kidney bean shaped hole?

    can you confirm slide is lifting on carb 3?

    have you tried swapping the 2 and 3 spark plug wires, to see if the problem follows the wire? you can also swap caps to see if it is the cap as a second step.
    also swap spark plug 4 with 3 to ensure known good plug, even if it is new.

    then trim back wire 3 to remove any corrosion at the end of the wire.

    is the mixture screw the same as the others course threads vs ultra fine? could be a carb from an older rack was swapped in.

    washer under main jet was it flat or cupped could be letting in extra fuel.

    main fuel and pilot fuel jets reversed? Been there done that.

    plug is wet is it black sooty too?

    have you ohmed out the ignition system
    The Ultimate Relay, Switch, Sensor, and Diodes Guide

    XJ650 models:
    Pick-up coils:
    1982-84 XJ650 Maxim: 650 ohms +/- 20% = 520 ohms to 780 ohms acceptable range
    Ignition Coils:
    Primary side (input from main wiring harness):
    2.5 ohms +/- 10% = 2.25 ohms - 2.75 ohms acceptable range

    Secondary side (spark plug wires, without their end caps):
    11K ohms +/- 20% = 8,800 ohms - 13,200 ohms acceptable range
    Spark plug caps:
    5K +/- 20% = 4,000 to 6,000 ohms per cap acceptable range

    Spark plugs:
    0 ohms per plug
     
  12. Jetfixer

    Jetfixer Well-Known Member

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    How I do a bench synch , I use 2 business cards cut in two ( IE you have 4 pieces) put one under each butterfly plate ...turn the idle screw in until it contacts the stop , adjust number one synch screw till you get a slight drag on the card leave it in place, move to number 2 do the same , move on to number 4 ..now turn idle screw in slightly ...now you should have a slight drag on all 4 pieces of card it the all feel the same your there. Remove the cards hold carbs up to strong light you should see a slight bit of light at bottom of butterfly plate. This should get you in the ball park. One thing I recommend I'm running 82 Honda CB750 coils , these can be bought new still and have replaceable plug wires. Cycle Recycle part 2 has the coils and wires and caps , the coils are around 40$ each these mount in stock location . One thing i also would recommend swap the plug cap from the hot cylinder to the cold cylinder...the cap maybe bad see if this follows problem. Cheers
     
  13. kerriskandiesinc

    kerriskandiesinc Active Member

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    84-91? 900R Kawasaki coils have replaceable wires too...I've run these successfully on some of my XJ's....

    Do NOT use silicone HT leads......I didn't like the way they performed, looked or...went together
     
  14. Polock

    Polock Well-Known Member

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    what's wrong with them? they come in colors, what more could a man ask for
     
  15. kerriskandiesinc

    kerriskandiesinc Active Member

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    Yes, the green matched my (re painted) green,black and gold Kawasaki perfectly...they seemed flimsy, didn't fit the plug cap screw very well....and looked like they were 'falling apart', internally.....maybe they've gotten better, since the 90's...?
     
  16. Timbox

    Timbox Well-Known Member

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  17. SM85

    SM85 Member

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    Hello everyone! Before I post this, I want to thank everyone with all their advice so far. I have taken the last few days to recheck everything mentioned here.

    I have dismantled #3 carburetor again, Fuel and Air jets are in correct position. All passages are still clear and clean. The vacuum slides open on all carburetors when cranking the throttle. Performed the bench sync. I even hooked up the vacuum line to the fuel tank again, checked it for damage and used hoseclamps to make sure a tight seal.
    The #3 cylinder still only runs when covering the air collection (Oval) port at top of intake mouth. So Strange.
     
  18. Ryengoth

    Ryengoth Active Member

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    Is there a secondary fuel tube in the bowl that could be clogged?
     
  19. XJ550H

    XJ550H Well-Known Member Premium Member

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    covering that hole would cut off air to main and pilot jet. that would mean you are sucking more fuel into the cylinder
     
  20. sybe

    sybe Active Member

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    you might want to check the jet sizes and spray starter fluid on #3 carb boot / engine manifold. if the engine surges then you have an air leak at the boot. if it still does the same then start spraying parts of the carb to make sure you arent leaking any air. The carbs are more finicky than an upset wife.
     

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