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.

Smoke from under engine?

Discussion in 'XJ Technical Chat' started by mshah0686, Feb 4, 2021.

  1. mshah0686

    mshah0686 Member

    Messages:
    33
    Likes Received:
    6
    Trophy Points:
    8
    Location:
    Texas
    I'm having 2 problems (2 that I've found) with my 1982 XJ750J. The bike has been sitting for about 2 months.

    1) After running (even at idle) for a couple minutes, smoke starts to come from under the bike near the oil pan/collector. I'm not sure if this is the exact location because I can't find where it comes from exactly.

    There doesn't seem to be any leaks on the engine that I can find.

    2) Whenever I blip the throttle to above 3k rpm, the rpms just stay there and don't come down. Sometimes they come down while riding. I don't think it's a stuck throttle cable since I can see the throttle shaft close on the carbs when the bike is not on.

    I tried spraying WD-40 around the boots for intake and out of the carbs but I didn't see a change in the RPM so not sure if it's a vacuum leak either. Where else could there be a leak?

    I plan on cleaning the carbs for the first time this weekend (I've only had the bike for 4 months) to see if there's a clogged jet.
     
    Last edited: Feb 4, 2021
  2. Franz

    Franz Well-Known Member

    Messages:
    2,232
    Likes Received:
    601
    Trophy Points:
    113
    Location:
    Scotland UK.
    Have you checked the oil level as you have recently got the bike? Are you sure it is smoke and not water vapour? Let the engine and exhaust get up to operating temperature as it has been sitting to see if it stops could be dampness in the exhaust collector. How far did you run the bike? Was the bike stored inside or outside?
     
    Last edited: Feb 4, 2021
    Jetfixer and mshah0686 like this.
  3. mshah0686

    mshah0686 Member

    Messages:
    33
    Likes Received:
    6
    Trophy Points:
    8
    Location:
    Texas
    Thanks for the response. Oil levels look good, I'm going to change it this weekend though.

    How can I check if its water vapor vs smoke?

    I ran the bike for about 2 miles (10 minutes ish) and a few minutes in the garage at idle. The bike was stored inside.

    I'm not even sure if the smoke is coming from the exhaust or the engine, is there a way I can check that as well?
     
  4. cgutz

    cgutz Well-Known Member

    Messages:
    1,134
    Likes Received:
    669
    Trophy Points:
    113
    Location:
    SE South Dakota
    For the hanging throttle - have you done a running synch on the carbs lately?
     
    Jetfixer likes this.
  5. mshah0686

    mshah0686 Member

    Messages:
    33
    Likes Received:
    6
    Trophy Points:
    8
    Location:
    Texas
    I have not. I'm buying a carb synch tool as well to try that out. Just curious, how would an out of sync carbs affect this?
     
  6. Fuller56

    Fuller56 Active Member

    Messages:
    405
    Likes Received:
    129
    Trophy Points:
    43
    Location:
    Cary, NC (winter) Harpursville, NY (summer)
    Water vapor will be white in color with very little to no odor and will dissipate much more quickly than oil smoke. Smoke will last longer, oil smoke will smell and generally is blue-ish. Smoke from an overly rich burning engine will be blacker in color and have a heavier gasoline like odor.
    John
     
    mshah0686 likes this.
  7. mshah0686

    mshah0686 Member

    Messages:
    33
    Likes Received:
    6
    Trophy Points:
    8
    Location:
    Texas
    Thank you for the explanation.
    Hmm it does not have a strong smell and it is white as far as I can tell. Should it eventually go away if it is water vapor?

    I'm not sure how burned oil should smell.
     
  8. Franz

    Franz Well-Known Member

    Messages:
    2,232
    Likes Received:
    601
    Trophy Points:
    113
    Location:
    Scotland UK.
    If it is water a hot exhaust system will dry it out that's why it is better if the engine and exhaust are at operating temperature or fully warmed up.

    Oil burning off happens when an engine has been rebuilt because the oil used to lubricate the cylinders is burned when the engine is started up. This is temporary. If a four stroke engine is always burning oil there is a problem with the oil control rings letting oil into the combustion chamber. This can also happen with worn valve stem oil seals. The most likely cause is water in the exhaust boiling off. Don't be concerned about oil at the moment. Let the engine run till it is hot to see if the steam l will call it disappears.
     
    mshah0686 likes this.
  9. mshah0686

    mshah0686 Member

    Messages:
    33
    Likes Received:
    6
    Trophy Points:
    8
    Location:
    Texas
    Got it, I'll let it idle for a couple minutes and see what happens. Out of curiosity, where would water have gotten into the exhaust system? It's been in the garage and it's air cooled.
     
  10. Franz

    Franz Well-Known Member

    Messages:
    2,232
    Likes Received:
    601
    Trophy Points:
    113
    Location:
    Scotland UK.
    Condensation when a hot exhaust is cooling down and there is water created during the combustion process. I would let it idle for half an hour. Exhaust systems rot from the inside out as combustion creates a situation where the metal can corrode although this takes a long time. Carbon dioxide and water are a by product of combustion in internal combustion engines.
     
    mshah0686 likes this.
  11. XJ550H

    XJ550H Well-Known Member Premium Member

    Messages:
    12,630
    Likes Received:
    3,601
    Trophy Points:
    113
    Location:
    Great North Woods
    there is a little hole on the bottom of the exhusst it is a drain see if yours is clogged up
     
  12. mshah0686

    mshah0686 Member

    Messages:
    33
    Likes Received:
    6
    Trophy Points:
    8
    Location:
    Texas
    Is it the small hole where the exhaust meets the collector? I can feel exhaust air coming out from there when the bike is running.
     
  13. XJ550H

    XJ550H Well-Known Member Premium Member

    Messages:
    12,630
    Likes Received:
    3,601
    Trophy Points:
    113
    Location:
    Great North Woods
    yes thats where water should drain. I would imagin the bike has to be on the centerstand for it to work correctly. if you feel exhaust coming out the holes are clear
     
  14. hogfiddles

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

    Messages:
    13,630
    Likes Received:
    4,320
    Trophy Points:
    113
    Location:
    near utica, new york
    Any oil that has seeped out of anywhere, like shift shaft, crank shaft seals, valve cover gasket, etc......will run down to the bottom side of the engine and the top of the exhaust.if it’s just sitting then when the engine is fired up, get hot, it will burn off, too.
     
  15. mshah0686

    mshah0686 Member

    Messages:
    33
    Likes Received:
    6
    Trophy Points:
    8
    Location:
    Texas
    Interesting. This is what I suspected as well. But I can't seem to see any oil leaks anywhere or an oil build up.

    I saw that you can use baby powder to find oil leaks? Is that a good idea?
     
  16. Franz

    Franz Well-Known Member

    Messages:
    2,232
    Likes Received:
    601
    Trophy Points:
    113
    Location:
    Scotland UK.
    Sump plug washer any oil leakage from it? Or the oil filter or oil cooler housing O ring?
     
  17. mshah0686

    mshah0686 Member

    Messages:
    33
    Likes Received:
    6
    Trophy Points:
    8
    Location:
    Texas
    So update:

    I pulled and cleaned the carbs (for the first time). It wasn't as complicated as I was aniticipating (except for when I installed the floats upside down the first time haha)

    But one the jets in the carbs was wrong, instead of a #43 it had a #40. This could a cause of a lean mixture correct, causing the high rev issue? I have yet to tune since the gunsen is coming from Chacal.

    Also, I bench synced the carbs and they were really out of sync. I have to do a proper tune with a gauge but I think you guys were right, they were very out of sync.

    I am yet to run it for a while to see the smoke issue.

    Thanks ya'll for helping a junior mechanic (20 years old)!
     
  18. hogfiddles

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

    Messages:
    13,630
    Likes Received:
    4,320
    Trophy Points:
    113
    Location:
    near utica, new york
    You’re getting there:)

    nice to see someone a bit younger learning these, and more importantly— LISTENING to the advise given when asking questions.

    Trust this— we have NO problem with ‘asking a million questions” when someone is willing pay attention to the answers:)

    welcome :)

    dfox
     
    k-moe, Franz and mshah0686 like this.
  19. k-moe

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

    Messages:
    18,855
    Likes Received:
    6,196
    Trophy Points:
    113
    Location:
    The City of Seven Hills
    Dust burns with white smoke too.
     
    hogfiddles likes this.
  20. mshah0686

    mshah0686 Member

    Messages:
    33
    Likes Received:
    6
    Trophy Points:
    8
    Location:
    Texas
    Ran the bike and did a carb sync. I noticed this puddle which I think is water dropping from the exhaust. So I guess the smoke was from this.

    As far as I could tell, there's no more smoke anymore!

    I don't have a YICs tool yet so the carb sync didn't make sense but the bike does run better than before. How important is it to get the needles close to each other? Here is how far I could get them.
    IMG_20210206_130622.jpg
    IMG_20210206_132143.jpg
     

Share This Page