Smokey breather

scott_jangers

Active Member
Hi all,

I'm getting smoke coming out of the breather on a CL350 which I purchased recently. I am I in the process of jetting the carbs and went for a 30 mile trip to test out the current setup/throttle positions. It was the first time I have ridden the bike. It has VM28 carbs with velocity stacks and the mufflers have been replaced with black 12" shorty ones. I did a cold compression test when I first got the bike home and both cylinders were on 175psi. Ignition timing has been done and oil level appeared okay.

I am all the way out on the mixture screws and at the lowest clip on the needle. The bike is a little rich but using a colortune it has a blue tinge. A smaller pilot and leaner needle is on its way.

It has a bit of hesitation in low revs and transitioning at 3/4 throttle maybe.

The bike ran fine until I got home and noticed white smoke coming from the breather, puffing out in time with the idling. It was an usually hot morning compared to the last few days.

I would like to continue jetting the carbs but I'm now a little scared or cautious to ride the bike before doing a few further checks. Can you give me some tips on what I should be doing next to work out the cause of the smoke?

My thoughts are to check oil is getting to the head/valvetrain and maybe check the compression again? Should I ride it again to see if it still occurs?

Thanks,
Scott.
 
From what I’ve read it can either be moisture in the crankcase or blow by from the rings. I have the same thing in my cb750. I’m getting 170 psi on all four cylinders on my bike. Maybe someone else will chime in.
 
Hi esmoojee. Yeah, I've searched about at other posts on here and Hondatwins and it seems that water condensation and blow-by are the top two causes. Understanding the symptoms and root cause is bit more tricky based on I've only ever ridden this bike once, and it was whilst messing about with carb jets. Personally, I'm not convinced I can tell whether it is either condensation or smoke for certain....

Is there a way to distinguish whether it is smoke or condensation?
How can I tell if I have moisture in the crankcase?
How can I tell if it's blow-by? Smell the oil for contaminates?

I do wonder if it's overheating due to the oil not getting to the top as it should, but imagine the best way to test this is to start up the engine with the tappet covers off? Is there one that is closer to an oil passageway than others, cylinder 2 intake maybe?
 
Next time it's smoking put your hand over the breather and let it condense on your hand. If it's water it will condense and be...well...water. If it's oil from blowby it will be an oily mess on your hands.
 
30 miles should be enough to burn off any condensation, I would think. Also check your oil level. Overfilling can cause this too. If you're getting blow-by, it would be coming out of your exhaust too.
 
Hey irk miller. I will double check the oil but was certain it was not too high.

No smoke from either exhaust, just the breather tube.

Would it be worth doing a warm compression test and then repeating with oil down the cylinder?

As soon as the replacement o-ring arrives my plan is to pop the right cover, check and clean the oil filter and give it an oil change. Got a can of that Engine Flush kicking about on a shelf that I was considering popping in, just before I change the oil, t to see if I can clear out more crap from passageways?
 
I guess a question should be how much smoke and is it smoke that travels or lingers. A little bit isn't out of the ordinary and as has been mentioned the condensation will cause it too. Fuel in the oil is also know to have an effect, but you would have to get fuel in there for that to happen. The previous suggestions about blow-by are because of crank case pressure, which would be rings or head gasket. Your compression test will certainly let you know if those are an issue.
 
irk miller said:
30 miles should be enough to burn off any condensation, I would think. Also check your oil level. Overfilling can cause this too. If you're getting blow-by, it would be coming out of your exhaust too.

This. Could also be getting too hot.
 
Thanks for the replies. The smoke lingers and travels a little. My understanding of blow-by is that carbon deposits built up in the chamber cause the rings to not seat properly. This increases the pressure in the crankcase and allows fuel and contaminates to get in, which cause smoke and oil to exit through the breather. Does this sound reasonable?

If stuff can get past the rings into the crankcase, then oil could get into the combustion chamber also? There is no smoke coming from the exhaust. Only the breather.

What I have a little confusion about is whether the pressure in the cylinder increases or decreases with carbon buildup messing with the rings? Would a build up of carbon cause the rings to tighten? Am I looking for a lower or higher than average psi on a compression test? As above, the only test I did was when cold and I had 175psi on both cylinders.

My plan is as follows....

Tests
1 - check oil level.
2 - remove tappet covers and start engine to observe oil getting to the cylinder head.
3 - ride bike up to temperature and observe smoke from breather - hand test.
4 - check plugs - lean or rich and oil.
5 - do a compression test with a warm engine.
6 - repeat compression test with a little oil in cylinder to observe any changes.

Actions
1 - use Seafoam spray to attempt to remove carbon deposits inside combustion chamber.
2 - use an engine flush treatment in the oil to clear out any crap in passageways.
3 - clean oil filter screen
4 - change oil with 10w40 mineral/semi-synth JASO MA oil.


Does this sound like a decent plan? Am I missing anything?

Thanks!
 
Well I checked the oil level and it was right on the top mark. I dropped 100ml out and it still smokes. I started the engine with the tappet covers off and noticed a couple of spots out of number 1 cylinder exhaust, but apart from that there wasn't much sign of oil getting to the top of the head. Plugs are good, brown and dry.

It's still smoking, and definitely smoke not condensation. It has a smell to it that is a bit like burnt oil and fuel.

Warm engine compression test next, and when I get a moment I'll try out the seafoam and give the oil a change and filter a clean.
 
Just a quick update. Blasted half a can of seafoam spray through the carbs this morning and a ton of smoke came out of the cylinders. Took the bike for a long ride and it seems to tick along a lot smoother but will do a compression test to see what changes it may have made if any.

Anyway, I or home and checked the breather pipe. It's no longer smoking like it was, and I put my hand over the end and it was definitely wet not oily. So I'm assuming the seafoam' made some improvement. I will do a full oil change and filter clean next and see if this has any affect on the condensation, but all in all, positive stuff.
 
So I did a warm engine compression test and got just a shade under 200psi in both cylinders. When I bought the bike as a non runner a month ago I did a cold engine compression test and got 175psi on both.

Not sure what’s happened here, if it’s the difference between cold and warm or before and after sea foam? What causes higher than normal compression readings? Valve clearances?

Anyway, bike’s running great (apart from a bit of tweaking with the main jet, cleaning the crap out of the tank, changing the seat, doing an oil change, sorting the rear brake....)
 
irk miller said:
Usually carbon buildup will give you high compression readings.

Another go with sea foam spray then!

Would it be normal for readings to change from 175 cold to 200 hot? Seems like a big jump for only three weeks especially as the bike only did a handful of miles.
 
More likely that the rings were slightly stuck and Seafoam released them. 200psi is pretty high though. Where did the compression tester come from? The reason I ask is that cheap ones often read really low or artificially high. loose tappets ie excessive valve clearances might contribute to that reading or worn cams or lots of carbon.
 
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