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Discussion Starter · #1 ·
i went for a 150 mile ride today in sunny So Cal on the 71 CB350 . It was around 90 to 100 degrees today and i rode the bike really hard but after a while i noticed that the bike was starting to act up. Here are the symptoms:

-slight loss of power
-lower idle
-lots of smoke off the breather tube

The bike didnt stall but it certainly wasnt running like it usually is and the smoke from off the breather tube was freaky. Pulled over to a bar for a few and after an hour got back on the bike and it was fine for about 30 hour and the smoke and symptoms came back. What does this mean?
 

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Sensei
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What are you current compression readings? (hot, fuel and key off, plugs out, choke open/off, throttle wide open)....
Smoke from the breather is a sign you are burning oil......weak rings/blow-by is a usual cause....
 

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Discussion Starter · #3 ·
66Sprint said:
What are you current compression readings? (hot, fuel and key off, plugs out, choke open/off, throttle wide open)....
Smoke from the breather is a sign you are burning oil......weak rings/blow-by is a usual cause....
A few weeks ago it was 180 on each side which i think is high for a 350 right? i checked the oil during the ride and it read higher than usual so that i might explain the white smoke but was about the loss of power and weak idle? is it because of timing? i write that because i did the timing using the static method and not with a timing gun/light.

let me know. thanks 66Sprint
 

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Yes, 180 is a bit high, but not unreasonable if it's a fairly fresh engine.....Of course, it could mean the rings were already "tight' and the extra heat of the long trip is making them "too" tight......It is the high oil level that has me worried......Are you SURE there is NO fuel smell to it?...thinned oil burns fairly easily and does make Blue/white smoke.....The lowered lubrication could account for less power as well ( the engine wastes power fighting the friction/additional heat....I'd re-run the compression test to see what it is now (when/during power loss).....Lack of adequate ring gap or piston clearance show up when the engine gets real hot....You could have cracked a ring....Check the oil for smell first...then test....
 

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Sorry to re-open such an old post, but I read a while back that "smoke" from the breather is normal, and that it's something to do with humidity condensing or something... Should I be troubled?

Also, out of curiosity, what does high compression mean? I ask because I have an old BMW airhead and got compression just above the "good" rating... but I just figured that was "better than good".

Thanks
 

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Some smoke (a very small amount) might be OK, but a large amount usually indicates ring blowby caused by ring wear. The breather is used to relieve pressures in the crankcase caused by the piston travelling downward in the cylinder during the intake and power strokes. The crankcase needs to "breathe" during operation.

Higher than normal compression can be caused by excessive carbon buildup on the pistons and combustion chambers. The carbon buildup can be caused by incomplete combustion or excessive ring wear, or just babying the engine. Sometimes a good hard run can clean it out. Carbon buildup can lead to piston damage if it's excessive.

..........Paul
 

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You haven't swapped out your Factory Coils for Aftermarket ones did you?

The reason I ask is I did and then wired the Polarity of the Primary Side backwards.

This caused excessive heating of the coils the bike ran but the performance degraded the longer I ran it. AND when I stopped I had excess smoke coming out the brerather tube.

Just a thought.
 

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kine8282 said:
A few weeks ago it was 180 on each side which i think is high for a 350 right?
I run my 360's (with 378cc conversions) around 210~220 psi and no problems (use 93 octane)
180 is no big deal, very small combustion chamber
set oil level half way between marks, too high and oil can touch flywheels which increases drag plus throws more oil onto cylinder walls than rings can cope with which increases drag even further and makes rings 'aquaplane' (easiest way to describe it)
 

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i've been riding my bike a lot the past few days...it's running pretty good...however, there's still smoke coming from the breather tube after about 20-30 mins of riding...it happens when I'm sitting at stop lights (I live in philly)...seems to run fine, but the smoke is still coming out of the breather tube...

what causes this besides bad rings? my carbs def need to be adjusted...could a bad air/fuel mix do this?
 

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If the smoke is coming out with a bit of pressure, you have a ring problem. If it is white, gentle puffs, I would call that normal. Water is a product of combustion and a little will get by the rings and condense in the oil. The water is boiled off in the crankcase and shows up as those gentle little puffs.

Prior to 1964, cars had the same system, called it a draft tube, and a little white vapor coming out of a running engine was normal then too. I owned a 64 Chevy Impala, it was the first year they had PCV on the 49 state model.
 

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right....newer cars pump the vapor through a smog pump and all that emissions crap right?

right now there isn't a tube on the crank case breather so it's hard to look at the smoke...it just comes up by the seat and gas tank...i'm going to put a hose on it tomorrow so I can take a good look at it...if the rings are bad, how do I check? I'm assuming a compression test..but i've never done that before...
 

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Seems a little high....My bike usually "puffs" with little velocity. this seems to be a steadier stream. Looks like you are bypassing the rings a little more than normal.

How is the compression? If the compression is good, I'd live with it a little longer. You may need a honing and rings, or maybe your rings are a little stuck....

If I had that issue, I'd be riding until the winter, then pull the cylinders and see if the rings are stuck. Good time to de-carbonize and clean up everything then.

Maybe some others have some insight on this too.
 

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I get at least that much. I installed new rings about 1000miles ago. Compression is good. I think it's normal...
 

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thrilhou said:
I get at least that much. I installed new rings about 1000miles ago. Compression is good. I think it's normal...
did you deglaze the cylinders? New rings on shiny cylinders will not bed in properly. A light hone is required with new rings.
 

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Mydlyfkryzis said:
thrilhou said:
I get at least that much. I installed new rings about 1000miles ago. Compression is good. I think it's normal...
did you deglaze the cylinders? New rings on shiny cylinders will not bed in properly. A light hone is required with new rings.
Checked and honed by bore-tech.
 

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Yeah my plan was to run it until winter and then look into it. I paid 500 bucks for this thing just to get me around Philly so if I do any damage to the engine I'm not too worried about it. I could always get another engine or have it rebuilt.

However I'd like to look into it a little and have an understanding of how it all works. How do I check the compression? I haven't because I've never done that before.
 

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A basic compression test is.easy to do. Engine should be warm, throttle all the way open, choke open (or.carbs removed), screw the tester into the plug hole and crank the engine until the needle stops moving. Do a search for more thorough discussions on compression and compression testing.
Btw, here is a video I posted else where with my engine smoking:
[youtube:14v8jzge]g0oGy0PAYTI[/youtube:14v8jzge]
 
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