White smoke

[Oscarg]

  I am looking to buy a cb 750 and today I looked at one that had a rough idle and white smoke. The guy tells me it wasn't smoking a last time it ran but it's been sitting a few months. Any ideas?

[TOOLS1]

Was it smoke, or steam? Welcome to the forum.
TOOLS

[Oscarg]

I think smoke a 81 cb 750 is air cooled ? Anyway the guy said another guy took a test drive and it smoked worse after a short ride. Are you suggesting water in fuel?

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   Oscar

On Sep 25, 2011, at 7:49 PM, "TOOLS1 [via Honda CB750'S]" <[hidden email]> wrote:

Was it smoke, or steam? Welcome to the forum.
TOOLS

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[Oscarg]

How do you tell smoke from vapor

[TOOLS1]

I was thinking condensation in the exhaust. You can tell oil burning by the smell. Also it will have darker tint, and hang in the air longer. If it is oil burning. Run a compression check. Also look at the spark plugs, They will show if the engine is burning oil.
TOOLS

[Piute]

 never seen a motorcycle put out WHITE smoke (riding 35+ yrs),
  So I  and
   Now this is BLUE or GREY ? O.K. seen this lots
Oil may leak into the cylinder chambers and ignite along with the normal gasoline/air mixture. Make sure that your gaskets and seals are not cracked or degraded and that you have not overfilled the oil.

not overfilled the oil.
  also as TOOLS mentioned water acually i think condensation in the oil that could cause WHT.,but not from setting only a few months ,have had bikes set 4-5 months and never happened,
   my '77' been setting 6yrs ,but I changed the oil before starting no prob.

  Since it's not yours and the guy really wonts to sell tell / ask him to change the oil and filter and just work another price IF it don't put out the same smoke,
  I'm just trying to save you from cracking it open could or might not be that seriouse ,hard to tell from here                                                 Good Luck ,                                      >>>Piute<<<N>>>Judose<<<
  I'm not no excpert on these 750s but there not water cooled ,

[shinyribs]

I have seen auto engines that,after sitting for extended periods,will put out white oil smoke. Its from where the rings freeze in the piston grooves and let some oil go by from not sealing properly.Its such a small amount that it is hard to see the usual blue/gray you would expect from oil. Like Tools said,it will still hang in the air.A little run time and a splash of Marvel Mystery Oil always cured it for me.Not saying that is what it is,just a thought.

[Oscarg]

Thanks for all the info guys. I have worked on diesel engine for forty year but know very little about gas or motorcycle engines so any help please. I didn't tell you the eng also had a rattle from right side of engine. if you have a dead hole from  carb clogged would you get white smoke and a rattle? Also can you repair just one hole ? Is it very expensive?

[Oscarg]

Thanks for all the info guys. I have worked on diesel engine for forty year but know very little about gas or motorcycle engines so any help please. I didn't tell you the eng also had a rattle from right side of engine. if you have a dead hole from  carb clogged would you get white smoke and a rattle? Also can you repair just one hole ? Is it very expensive?

Thanks Oscar

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On Sep 25, 2011, at 10:13 PM, "TOOLS1 [via Honda CB750'S]" <[hidden email]> wrote:

I was thinking condensation in the exhaust. You can tell oil burning by the smell. Also it will have darker tint, and hang in the air longer. If it is oil burning. Run a compression check. Also look at the spark plugs, They will show if the engine is burning oil.
TOOLS

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[TOOLS1]

It costs about the same to rebuild the whole top end as it does to just do one cylinder on these bikes. The carbs being out of sync will make these things sound like they are flying apart. However the with the white smoke, I would run a compression check, or at least pull the spark plugs before buying it.
TOOLS

[Oscarg]

What's a baseball price to build top end in parts? Is some a mechanically inclined person could do?  

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   Oscar

On Sep 26, 2011, at 9:58 AM, "TOOLS1 [via Honda CB750'S]" <[hidden email]> wrote:

It costs about the same to rebuild the whole top end as it does to just do one cylinder on these bikes. The carbs being out of sync will make these things sound like they are flying apart. However the with the white smoke, I would run a compression check, or at least pull the spark plugs before buying it.
TOOLS

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[Peterwh]

Maybe they just elected a new Pontif! :-)

[TOOLS1]

Pope TOOLS 1. I like that. Any competent person should be able to handle a top end job. The only problem on the DOHC is setting the valves. They are shimmed where as the SOHC is adjusted with a screw, and a lock nut. Ball park would be $125.00-150.00 in parts (Gaskets, and rings). What ever a shop would charge, for a valve job. I doubt it would need bored, and new pistons.
TOOLS

[Daddyman]

AWE! I hate shims, I had a 450 with shims and it was a pain in the butt.  Guess I wont be lookin for a DOC.

[Piute]

I hear ya Daddy 'o' guess the 80 might be out of the future

[Oscarg]

Well I talked the guy down to 1000.00 and the sheet metal is straight and the chrome and aluminum looks good. So I should come out alright if I can rebuild it myself right?

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   Oscar

On Sep 26, 2011, at 4:41 PM, "Piute n Judose [via Honda CB750'S]"<[hidden email]> wrote:

I hear ya Daddy 'o' guess the 80 might be out of the future

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[Piute]

 May be a great winter project for you,Myself have never did a tear-down other then carbs on these 750s,But one of the main reasons I wonted one(besides Pop owning one back in 70s)Was I believed I could do all the work myself with help of the INTERNETthere are lots of fix-it sights and Tech-Tips out there,and best of all The guys on this sight,
  I couldn't buy a bike with-out seeing it, bought mine from what I SEEN all stock and unmolested
 but Fuses (boxe)changed,I no nothing about desial engines except how to use a glow light on a
440 cat.

  >>>Piute<<<

[Oscarg]

Well I rode them from the early 70 to mid80s when I get this it will be my fifth cb750 but my first dohc

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   Oscar

On Sep 26, 2011, at 9:30 PM, "Piute n Judose [via Honda CB750'S]"<[hidden email]> wrote:

 May be a great winter project for you,Myself have never did a tear-down other then carbs on these 750s,But one of the main reasons I wonted one(besides Pop owning one back in 70s)Was I believed I could do all the work myself with help of the INTERNETthere are lots of fix-it sights and Tech-Tips out there,and best of all The guys on this sight,
  I couldn't buy a bike with-out seeing it, bought mine from what I SEEN all stock and unmolested
 but Fuses (boxe)changed,I no nothing about desial engines except how to use a glow light on a
440 cat.

  >>>Piute<<<

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[Oscarg]

I don't have a compression testerso if I pull the plugs what should I be looking for?

[shinyribs]

If you have a bad or broken ring it will show up as oil deposits. A fuel fouled plug may look wet or sooty and sometimes flaky.Sometimes it kinda hard to tell the difference between fuel deposits and oil deposits.Oil will always be wet and slimy.If its fuel,and you rub it across your palm,it will eventually dry off.Oil will not.Oil oughta look wet,dark and slightly lumpy usually.Whereas fuel will look more sooty/flaky than it does lumpy


wow...that came out horrible....hope i didnt confuse things more