Results 1 to 14 of 14

Thread: R90/6 76 - smoke signals

  1. #1
    Registered User plehman's Avatar
    Join Date
    Nov 2006
    Location
    Arlington, MA
    Posts
    148

    R90/6 76 - smoke signals

    Had a bit of time on my hands so I replaced the second, less bad side, push rod seals. Nice. No more oil on the sides and bottom of the pan.

    While I was at it noticed the left cylinder spark plug was black. Not the case on the right plug. Black is too rich - or so I think. After putting everything back, adjusting the valves a few times to get them "singing to me" and it was running nicely. So I pulled out my home made carb vacum sensor and worked on the balance, particularly in terms of rich/lean.

    With the carbs sucking equally, I dropped the left side down until it "bogged" then back it off a bit. Not too rich, not too lean. But I just noticed it's still smoking!

    Question. Other causes for smoking? could it possibly be rings or something.

    76 R90/6 40,000 miles only. Doesn't burn oil. Usually sits on the center stand.

    thanks guys.
    Attached Images Attached Images

  2. #2
    Administrator 20774's Avatar
    Join Date
    Sep 2005
    Location
    San Antonio, TX
    Posts
    12,896
    Worn guides? I seem to remember there are some on-road tests for this. Probably something to do at dusk, maybe with a partner behind you in a car. If you see smoke on acceleration, that would be rings. If you see smoke when you shut the throttle down while coming down a hill, etc., then that would be the guides.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  3. #3
    #4869 DennisDarrow's Avatar
    Join Date
    Jan 2006
    Location
    Sugar Valley, Ga
    Posts
    1,062
    Please tell us that you are doing all of that carb tuning with a very strong fan blowing across your cylinders. Yes, they do overheat.........God bless....Dennis

  4. #4
    Registered User plehman's Avatar
    Join Date
    Nov 2006
    Location
    Arlington, MA
    Posts
    148
    Well, I try to work quickly and in short bursts. Even take it for a short cool down. Never run for longer than a minute or two without moving.

  5. #5
    Registered User lmo1131's Avatar
    Join Date
    Jan 2010
    Location
    Pismo Beach, CA
    Posts
    3,006
    Please tell us that you are doing all of that carb tuning with a very strong fan blowing across your cylinders.
    ... and that you've undertaken your adjustments after thoroughly warming up the engine.

    A twenty-mile jaunt is usually considered sufficient; warming it up in the garage is not.
    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
    1973 R75/5 - original owner

  6. #6
    Registered User plehman's Avatar
    Join Date
    Nov 2006
    Location
    Arlington, MA
    Posts
    148
    I usually adjust for rough or low idle when cold so it doesn't race when fully warmed up. But am still worrying that it's more than adjustment to get any smoke at idle.

    Checked the book and a value guide is the maximum difficult operation (5 wrenches). And it's for high miles bikes which this isn't. I gotta think this is mixture.

    Will work on that some more.

  7. #7
    Registered User
    Join Date
    May 2012
    Location
    VA
    Posts
    248
    I have experienced the same smoking on my left cylinder when synchronizing the carbs using the shorting method. After the left cylinder was shorted then started running, white smoke came from the left exhaust for a bit. After clearing the throttle and running for a short while it cleared up.

    I think the smoking comes from messing with the fuel/air mixture. Valve stem leaks usually cause smoke on startup after sitting. It's best to pay attention and observe how the engine behaves for a while and not make any snap judgements. Even with the valve guide seals leaking, the engine will burn little oil and will run a long time.

    But, things like smoking a bit and leaking oil really bother some folks. The valve stem seals are not that difficult to replace - in the sense that the heads are removed then sent to a shop for replacement. I expect even a local automotive machine shop would install new valve guides when provided with a disassembled head and new guides. However, that generally starts the ball rolling with looking at new valve seats, valves, springs, and ends up with a head rebuild. Head rebuilding costs ~$200 each.
    Stan

    AH# 13238

  8. #8
    Administrator 20774's Avatar
    Join Date
    Sep 2005
    Location
    San Antonio, TX
    Posts
    12,896
    Quote Originally Posted by Stan_R80/7 View Post
    I expect even a local automotive machine shop would install new valve guides when provided with a disassembled head and new guides.
    It's a debatable issue and has come up before. Some will say a head is a head, but for my money, I would be sure it got into the hands of someone who does BMW motorcycle heads for a living. There are enough differences and nuances that I'd want an expert for this type of thing.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  9. #9
    Registered User
    Join Date
    May 2008
    Location
    B.P., MN
    Posts
    713
    Could be wrong, but, the highest intake vacuum occurs at idle, and when backing off throttle, say, when ripping down a hill at 5K, and closing the throttle?

    That's when a loose intake valve guide will shoot hot oil into the intake runner, and poof, there goes the smoke. Can you ride'm like this? Watch the oil consumption, and prepare for some headwork. IMHO.

  10. #10
    Curmudgeon At Large Bobmws's Avatar
    Join Date
    Mar 2003
    Location
    Astatula, FL
    Posts
    1,112
    Quote Originally Posted by plehman View Post
    I usually adjust for rough or low idle when cold so it doesn't race when fully warmed up. But am still worrying that it's more than adjustment to get any smoke at idle.

    Checked the book and a value guide is the maximum difficult operation (5 wrenches). And it's for high miles bikes which this isn't. I gotta think this is mixture.

    Will work on that some more.
    Your valve seats were designed for use with leaded fuel, the lead being a lubricant. Having to run unleaded will hasten the wear, so yeah you could have a problem even at your lower mileage.
    Bob Weis
    '04 K12RS - Hannigan Hack
    www.earplugco.com

  11. #11
    Registered User
    Join Date
    May 2012
    Location
    VA
    Posts
    248
    My theory about what is happening:

    When tuning during extended idling, if the heads get hotter than normal due to inadequate air flow the oil thins and more easily goes into the cylinder via the valve guides and causes smoke. This will not occur with adequate cooling. It's a pretty simple theory to validate or not.

    I think that was happening to mine. After rearranging the cooling fan, the smoking never recurred. Also, my bike does not smoke on starting and the plugs look good. YMMV.
    Stan

    AH# 13238

  12. #12
    Registered User plehman's Avatar
    Join Date
    Nov 2006
    Location
    Arlington, MA
    Posts
    148
    Back to basics. After adjusting for rich/lean and a good long ride, I rechecked the plug and the dark black is gone, replaced by a nice brownish color.

  13. #13
    Registered User lmo1131's Avatar
    Join Date
    Jan 2010
    Location
    Pismo Beach, CA
    Posts
    3,006
    After adjusting for rich/lean and a good long ride,
    woo hoo!! ... let's hear it for good long rides
    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
    1973 R75/5 - original owner

  14. #14
    Registered User mpmarty's Avatar
    Join Date
    Mar 2008
    Location
    Camas Valley Oregon
    Posts
    1,054
    I dunno, can you smell the smoke? Is it fuel or oil?
    Marty - in the western Oregon mountains.'06RT, (gone '04RT, '86 Venture Royal, '81 Yamaha Virago920, '82Suzuki GS1100GK, '76 Suzuki GT750, Triumph 750 Bonneville, BSA Road Rocket 650, 61" Harley knucklehead)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •