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cold blooded at first - then pops warmed up

Discussion in 'XJ Technical Chat' started by turpentyne, Jan 21, 2019.

  1. turpentyne

    turpentyne Active Member

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    I need some outside opinions on next steps with this '82 750 Maxim. Maybe there's a few suggestions before I pull the rack back out.

    The carbs were completely rebuilt -- church clean. Racks broken down, replaced jets, everything cleaned - including the itty bitty holes people tend to miss. pilot fuel jets are #41 , main fuel jets are #120. Stock airbox, new spark plugs, shims adjusted. Carb tuned, color tuned. rain danced. The whole shebang...

    But... even with that effort, I go out to start it up each weekend and fiddle with tuning, but no luck. I have to spray starter fluid into the airbox and try about 10 - 20 times to get it to start. With the choke full on. And it's about 60 degrees out.

    Then, once it starts, it does just fine. warms up for a few minutes. Once it's good and warmed, I can hear a few pops out the right exhaust when I blip the throttle. While I was color tuning, I could see it was likely the #3 cylinder. The mixture screws are all just a hair past 2 1/2 turns. I tried turning that back and forth on carb 3 to get rid of the pop, but it didn't matter.

    My suspicion is that I need to pull the carbs off and go through the little tiny enrichment hole again. But I did the carb-spray test, and they seemed good. I also may want to replace the carb 3 mixture screw. The others are new. that one seemed good enough to clean and leave alone, but maybe that was a bad decision.
     
  2. k-moe

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

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    Check for exhaust leaks.

    Pics of the plugs would be helpful. Uee a neutral background.

    Did you prime the float bowls prior to attempting to start the machine?
     
  3. turpentyne

    turpentyne Active Member

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    I'm not using the gas tank, just a little fuel-safe plastic container with a manual on off switch. Since it's not working off vacuum, maybe that's part of the problem?

    I did see a little white smoke coming from around where the exhaust comes out of cylinders 3 & 4 - I hadn't thought about it yet, thinking maybe it was just a little condensation.

    I have been putting off messing with exhaust because I'm a little gun-shy about breaking bolts.
     
  4. XJ550H

    XJ550H Well-Known Member Premium Member

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    did you plug the vacuum line?
     
  5. turpentyne

    turpentyne Active Member

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    Yep, it's plugged. and they're all new rubber caps - the old ones were fossilized. Also, checked for vacuum leaks and nothing seems wrong, there either.

    Next I think I'll grab a squirt bottle and check for exhaust leaks
     
  6. tabaka45

    tabaka45 Well-Known Member

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    Sounds to me like you still have a problem with the carbs, most likely the pilot circuit. Also, check for a leak around the intakes. I had a gasket with about 1/2 of it missing.
     
  7. jayrodoh

    jayrodoh YimYam Premium Member

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    At first I read the title as "my dad didn't want me getting a motorcycle at first and then he warmed up to the idea"

    LOL
     
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  8. XJ550H

    XJ550H Well-Known Member Premium Member

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    did you clean out the wells in the carb bowl that the tube goes into? that's what feeds the enrichment circuit (choke)
     
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  9. turpentyne

    turpentyne Active Member

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    Yep cleaned the wells, cleaned the tiny enrichment circuit holes. I can't think of a part I didn't clean.

    I am a little concerned that after wet-setting it and putting it on the bike, I was forced to wait two or three weeks before getting back to the bike and starting it up. I wouldn't think 3 weeks would be enough for any leftover fuel to gum anything up... but, heck... anything's possible.

    If I have enough light when I get home from work some night his week, I'm gonna check for exhaust leaks and check that off the list. if that's good... well, I'm suspecting I need to pull the carbs and clean the bowls again just in case. Simple enough, aside from the annoyance of it all.
     
  10. XJ550H

    XJ550H Well-Known Member Premium Member

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    did you clean the enrichment tube? no tiny holes in the enrichment circuit except in the tube are you talking about the pilot jet and mixture screw holes on the top of the throat by the butterfly disc?

    did you replace the o rings on the mixture screws spring then flat washer then o ring onto the screw.

    then the bench sync?
     
  11. XJ550H

    XJ550H Well-Known Member Premium Member

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  12. turpentyne

    turpentyne Active Member

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    Every piece of rubber has been replaced. All jets are new. Cleaned every orifice possible in the body, in the bowl. This was a complete soup-to-nuts rebuild.

    Not to say it doesn’t need to reinspected, but this is a case of hospital clean, and still a little fussy
     
  13. Rooster53

    Rooster53 Well-Known Member Premium Member

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    Even with an external tank make sure the carbs are actually filling. A week is long enough for the gas to evaporate from the bowls. Use a clear tube to verify the bowls are filling all the way. Bowls not full makes for a hard start cold.

    What did you see with the color tune on #3 that made you suspicious? All new rubber... does that include the intake manifolds with new gaskets?
     
  14. turpentyne

    turpentyne Active Member

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    Got home early enough, and just used the spray bottle of soapy water method, and didn't see any obvious exhaust leaks, at the heads.

    At four days between, it wasn't quite as hard to get her going, but still required the starting fluid.

    I've got clear hose on there, and and I turn it on then wait a couple minutes for the fuel to fill. Maybe I'm still being too impatient. ... oh! wait... do you mean attaching a hose to the drain plug, like when wet-setting? Why the heck didn't I think of that! Yeesh!

    At the same time I hear pops, the color flashes white for a second, then goes back to blue. None of the other plugs did it.

    Everything seems close to a basically decent tune, except for the popping when it warms up and I give a little throttle. I presume a touch lean.

    Maybe, this weekend I need to just pop the carbs off and clean things for kicks. It'll give me a chance to replace the mixture screw on #3 with a brand new one, too. (unless someone's successfully replaced that and the washer/o-ring while on the bike?)
     
  15. turpentyne

    turpentyne Active Member

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    Missed this question... No, They're still the manifolds that were on there. I just meant all the rubber parts within carb. But, they've been coated with high-temp RTV and wrapped with high-temp silicone tape. I just double checked for vacuum leaks, and nothing... or at least nothing findable with the carb cleaner spray method.
     
  16. lostboy

    lostboy Well-Known Member

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    I have had a pick up coil fail when it got hot. When it failed it would back fire. Yours might be failing intermently. Just a thought.
     
  17. XJ550H

    XJ550H Well-Known Member Premium Member

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    have you tried a new spark plug or swapping the plug with another to see if the problem follows the plug?

    you can also plug wire 2 and 3 see if the problem follows the wire and cap.
    if it does
    then just swap the caps see if the problem follows the swapped part.

    this would not address the lean then blue colors #3 cylinder do yo have the vacuum hose connected to cylinder 3?


    do you have the stock air filter?
     
    Last edited: Jan 23, 2019
  18. turpentyne

    turpentyne Active Member

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    Stock airbox and filter, brand new spark plugs and brand new plug caps. But, I'll try switching them around - they could be bad for all I know.

    Right now all four vacuum ports are blocked, since I'm just running a simple fuel line from a container.

    Cool. a couple things to try this weekend. I haven't replaced pickup coils, so that's worth looking at, too.
     
  19. Rooster53

    Rooster53 Well-Known Member Premium Member

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    Yes, that is what I was thinking. It's the best way to make sure fuel is really flowing and the bowls have filled.

    Another thought on cold start after sitting is low compression. Have you ever checked the compression?

    +1 on the electrical suggestions above just to rule those out as a cause of the popping. After that, maybe try backing the mixture screws for 3 and 4 carb out to around 4 turns to see if it cures the popping.

    And as k-moe suggested looking at the plugs might provide a clue even though it sounds like you haven't really made it out for a ride as of yet.
     
  20. turpentyne

    turpentyne Active Member

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    ok.. looks like I've got a beginner question...

    Before starting up the bike and trying a couple things, I'm checking the pickup coils, and I decided to check out the ignition coils and get that possibility out of the way.

    Pickup coils seem (mostly) good. I've got 6.58 ohms at the orange wire, and 6.69 at the grey. Even though I'm getting spark, I figured I might as well check ignition coils since I was at it.

    For primary, both coils gave me 2.8 ohms. Then, testing for secondary... I got nada, zip, zilch, OL.

    I tested a few ways - I tested from the pigtails to the plug cap, I tested pigtail to the wire - with plug removed. Then, I put the pigtail back and tested between wire #3 copper and wire #4 - both through the cap, and without the cap. They've been trimmed back to clean metal, and the caps are brand new.

    So my conclusion is... I'm doing something wrong. :)

    EDIT - on a side note, I just attached a clear tube to #1 carb, and that most definitely is the starting issue. It's not pulling gas into the bowl. What little bit was sitting in the bowl from last weekend came out, and that's it. Choke is on, and I gave it a couple tries starting, to see what happened. Opened the cap of my fuel container, in case vacuum wasn't letting it flow. Thoughts?
     
    Last edited: Jan 26, 2019

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