Topic: smoke from breather/gas in oil has me stumped...need help from the experts!

[johnspeck]

ok guys, a new problem today has me a little puzzled.

my cb350 twin has been running great.  however, on the way back from a weekend camping trip a couple weeks ago, the engine seemed to 'hiccup' once, then back to normal.  this was after a 70+ mile ride at 65-70 mph avg.  just seemed to burp, pause, then fine.
later that night, my right cylinder stopped firing.  the engine sounded 'muffled' and wasn't making power.  i was limping it back home when the cylinder started firing again, then crapped out.

i noticed my breather tube had puked some oil.  hmmmm....

i pulled the plug, and it looked to have some oil fouling on it...not a lot, but noticeable.

i checked the compression on that cylinder...180+  i checked for spark.  it had spark.  carbs are clean.
so i check the valves, since i'd recently adjusted them.  the exhaust valve clearance for the right cylinder was at maybe .010  i readjusted all the valves (.003 intakes, .004 exhausts per hondaman rec's), installed some new plugs, and changed the oil.
i did notice some little bits of metal in the oil drain pan, but none in the filter.

it seemed fine afterwards.  until today.

as the bike was warming up for my ride home from work, i noticed a significant amount of smoke coming from the breather tube.  it didn't go away after warming up on the ride home, but the bike seemed to run fine.

i re-checked the compression in both cylinders...over 180 each.  the left cylinder plug looks great.  the right is maybe a little oily, or at least a little darker than the left.
i check the dipstick, and i notice the level is higher than it should be, which it wasn't when i changed it last week, and it seems noticeably thinner (it drips off the dipstick quickly).  i put a little in a can and tried to see if it would burn, nope.  but it does smell gassy.

i've just drained and changed the oil, and i'm getting no smoke from the tube when i fire it up.  i haven't re-checked the valve clearances yet.

what could be causing me to get gas in my oil and smoke from the breather, if the compression is good, the carbs are brand new as of june and very clean, the floats aren't sticking and there's no overflow, the petcock is brand new...no gas leaks that i can see anywhere?  the valves were readjusted last week, and i had a valve job done when i redid the top end.  i'm stumped!

[Terry in Australia]

Well mate, if your oil level is coming up and it smells like gas (and I'm betting your gas level in your tank is going down) it's a safe bet that while you're sleeping, your new petcock is leaking (if turned off?) fuel into your carbs, the fuel is running into your cylinders, seeping down past your rings, and filling up your sump.

It's happened to me too, once with my CB750K1, and once with my Suzuki GS1000S. Get a "kit" for your petcock and maybe new needles and seats (fuel valves) for your carbs, and don't forget to turn the gas off, and it should be fine. Don't ride it with gas in the sump, as it'll wash all the oil off your bearings and kill your engine, not to mention the chance of a possible explosion. Cheers, Terry.

[johnspeck]

Well mate, if your oil level is coming up and it smells like gas (and I'm betting your gas level in your tank is going down) it's a safe bet that while you're sleeping, your new petcock is leaking (if turned off?) fuel into your carbs, the fuel is running into your cylinders, seeping down past your rings, and filling up your sump.

It's happened to me too, once with my CB750K1, and once with my Suzuki GS1000S. Get a "kit" for your petcock and maybe new needles and seats (fuel valves) for your carbs, and don't forget to turn the gas off, and it should be fine. Don't ride it with gas in the sump, as it'll wash all the oil off your bearings and kill your engine, not to mention the chance of a possible explosion. Cheers, Terry.

thanks for the reply terry.

the petcock is a brand-new piece from honda, and i turn it off every time i turn the engine off.  i absolutely never forget that, i've read so many posts detailing the results.

that's what has me stumped!  how is gas getting into the oil if the floats aren't sticking, the petcock is off every time i turn the engine off, the carbs are mikuni vm30's bought brand-new this summer, with all new parts?

my gut tells me something related to valve issues.  i missed a shift a couple days ago, and got close to redline if not over by a bit...i *do* ride the bike pretty hard, with regular high-speed runs and i usually shift around 7k on the tach unless i'm in traffic.

i always let the bike warm up before i ride, i always let the bike run for 45 seconds when it's warm to ensure the top end is getting oil...i regularly change the oil and clean the filter...  the engine only had around 5-6k miles when i did the top end rebuild.

i'm curious...and sorta worried, i rely on this little gal to get me to and from work every day.

[kghost]

Well just because parts were new last year doesn't mean thier not leaking this year.

The New carbs/petcock may have sat on the shelf a while.

I agree with Terry.

Pull the hose off the petcock and see if it drips in the off position.

[bucky katt]

that 180 pounds of compression sounds awfully high. one of the things that can cause an excessively high compression reading is lots of oil in the cyilinder.

[johnspeck]

that 180 pounds of compression sounds awfully high. one of the things that can cause an excessively high compression reading is lots of oil in the cyilinder.

ok.  take a look at this:



that's a cold compression reading on the right cylinder.

i started the bike this morning, and it sounded like the cam chain needed re-tensioning.  plus a slightly off idle every now and then.

went to adjust the tensioner (engine off), rotating crank to proper spot.  i'm hearing a weird noise from the left cylinder, not normal compression/exhaust cycling sounds.  then the left air filter starts breathing.

check the oil after changing it two days ago, might smell a little gassy, might just be in my head.  feels normal viscosity, not thin.  but something's up...  and i should be at work right now, but the bike has me thinking it shouldn't be ridden in this state.

[bucky katt]

wow, thats pretty good compression. dumb question time......is the motor stock or does it have high compression/big bore pistons?

[w1sa]

+1 to previous comments regarding likely fuel tap problem.

I think the sounds you are hearing are normal but accentuated by the higher compression, pods and also the fact that you are focussing on them.
I have a twin with two fuel taps. One is new. The older one has age but not a lot of use. It leaks internally and allows fuel to reach the fuel lines when turned off. (Fortunately the carb bowls have overflow tubes)
Float valves are designed to prevent fuel entering the bowls when the fuel level reaches its float set height. They can prevent fuel entering the carbs for long periods, providing the valves/valve seats/floats are in perfect condition and adjusted correctly. Any less than perfect seating, float height adjustment or debris fouling will allow fuel to enter and overfill the bowls. The tank tap also takes unnecessary pressure off the float mechanism when the bike isnt being used.
Without overflow tubes, the fuel will rise to a level where it enters the inlet tract and flows to the cylinders, eventually seeping past the rings and into the sump. This is the only real way fuel gets into the oil.  Raw fuel in the cylinder will cause unnecessary scouring/scraping of the cylinder walls.

As Terry suggested, the next thing you should do is disconnect the fuel line from the carbs and verify there is no seeping/dripping with the tap in the off position. If leaky, stick a container under the line overnight and see what the volume is. It can be surprising.

[johnspeck]

wow, thats pretty good compression. dumb question time......is the motor stock or does it have high compression/big bore pistons?

stock motor/pistons/cam/CR, new rings/hone, valve job, gaskets, etc.. .top end rebuild.

[bucky katt]

maybe someone a bit more experienced than me on these motors will chime in but 180 pounds sounds WAY high for a stocker, new rings and all, sounds like its way too high. i wasnt saying i doubted the readings you were getting, just that theyre high. my k4 750 motor with fresh rings only went in the high 150's or low 160's, i cant remember now.

[johnspeck]

maybe someone a bit more experienced than me on these motors will chime in but 180 pounds sounds WAY high for a stocker, new rings and all, sounds like its way too high. i wasnt saying i doubted the readings you were getting, just that theyre high. my k4 750 motor with fresh rings only went in the high 150's or low 160's, i cant remember now.

150 is minimum compression in my shop manual.

[chickenman_26]

150 is minimum compression in my shop manual.

Mine too. My CL350 had 175 psi right after a top end overhaul. 180 is fine. Maybe the float in one carb has absorbed fuel and sank. Did anyone blow compressed air in through the air screw hole? That'll foul up a float, but good.

Stu

[tbpmusic]

[chickenman_26]

ok guys, a new problem today has me a little puzzled.

We haven't heard from you in a while. How's it going?

Stu

[754]

A few things..
re -comp guages.. a number is just a number, difference between cylinders, or over time with same guage, is far more telling..

 when I rode a CB 350, I had a few, rode them a lot, but its been 25 + years..

 .. I had to reset my mixture screws, every 2 weeks..

 ..I dont think I ever went 4 months outa a few years without seting the points.

.. losing a cylinder was not unheard of... I just thought they are like that!.

... way more working on than the 750..IMO..

[Hush]

My partner's Suzuki GSX400L came to us with a sump full of gas/oil mix which puzzled us initially.
We did an oil change and a few weeks later again the sump was full of gas and oil mixed.
I spoke to the guys at Suzuki and they told me to renew the "O" rings that surround the float valves (I don't think any Honda had these) and the "O" ring that surrounded the fuel tap.
It hasn't occurred again since.
One tell tale sign was gas in the air filter box, the gas was leaking down and flooding the carbs, the gas leaked past the valves and washed down into the sump.
Hope you got yours cured by now.

[johnspeck]

i've been working so much lately, i haven't had much chance to even open the garage door.

i changed the oil and rode the bike, since i had friends in from out of town and needed transportation.  no problems.  bike is back to normal, it seems.
then on my last ride, smoke again from the breather.  oil smells gassy.  bike has been sitting since.  the boss is feeling generous, so he's been picking me up for work.

when i have a day off, i'll pull the fuel lines and route them to an empty water bottle.  petcock off overnight, see if any fuel is leaking from there.
my floats are set the same, and i haven't noticed any fuel from the overflow tubes.  i'll shorten the tubes and make sure they're all the same length.

i can set the floats lower, but i'm not noticing any problems with performance, so i'm kind of hesistant.

as far as the smoke issue, i'm thinking i'm just going to have to bite the bullet and pull the engine apart.  at the least, i want to make sure i haven't done any damage with the gassy oil.  i figure the problem is probably something valve related, as i have good (too good?) compression.  i'll check both cylinders and make sure they're close, but they seemed good on last check a couple weeks ago.

i wanted to do a tear down this winter, to address some cosmetic stuff (weld frame and powdercoat, rewire bike with custom harness, redo seat and undertray area), so why not just go ahead and rebuild the engine while we're at it!?

i've still got some bills to take care of before i can sock any money away for the project, but i'll be boring and fitting oversized pistons and rings, deck the head and cylinders to correct a small weep from the head gasket (a little bump in compression won't hurt), new valve components, maybe a touch of head work (suggestions?), new clutch.  i'd also entertain an early cam if someone has a line on one.

[Terry in Australia]

Just fix your fuel leak first mate, that's all that's wrong with it. Cheers, Terry.

[johnspeck]

update:

petcock is not leaking.  at all.
float bowls aren't too high.

oil is still gassy smelling.  smoke still coming from the breather when the bike is warmed up.

the only thing i can think is, the carbs are still too rich at cruising throttle positions, and i'm fouling the oil.  unburnt gas on the cylinder walls making it's way into the oil?

will recheck warm compression on both cylinders today, after i check the valve clearances cold (again!).
then it's back to plug chops and messing with carbs.  i never tried the smaller needle jets i ordered a while back.  when the weather cooled off, the plugs started looking better.  still, the midrange was always too rich, and if i've got good compression and no leaks from the petcock, that's the only way i can think that gas is getting into the oil.  i'm getting zero overflow from my carbs through the hoses (checked for kinks in routing, etc.)

i'll try leaning out the mids, since that's where i do 90% of my riding, and it's been an ongoing problem.
hope my stupid issues will help point some other people in the right direction if they run into the same problems.  thanks for all the input and help, sohc4.

[754]

With stock carbs, it may not be jetting..
 Check your diaphrams for tears or leaks, if that is the case the slide will react wrong, if they are dragging, it will be a lot richer..

[johnspeck]

not stock carbs.

[kghost]

John did you check the carb overflows to make sure they weren't clogged?

Its possible I guess to have it too rich and get a gassy smell to the oil.....but unlikely.

If it were really rich you'd see it on the plugs.

I've got a picture of your bike but I don't remember what type of carbs it had.

[johnspeck]

carb overflows look good, will recheck.
plugs looked decent once the weather cooled off.  still a little rich, but not black and sooty like they were in the middle of the summer.  more a lighter gray.
i'm stumped.  bike felt underpowered on the freeway yesterday.  still have smoke from the breather once bike is warmed up.
if i can get motivated to hit the garage, i'll try some smaller needle jets today...recheck compression in both cylinders.

[kghost]

How many miles since Top end rebuild?

What type of Carbs?

Wheres your jetting at now?

[johnspeck]

How many miles since Top end rebuild?

What type of Carbs?

Wheres your jetting at now?

not sure of mileage, since i don't have a functioning speedo.  i would guess i've put at least 1000, likely more since the rebuild.  i was taking the bike to and from work almost every day this summer from austin to manor and back, for at least a month.  conservative guess, let's say 30 miles daily...900 miles.  plus the ride from austin to luckenbach for the harvest classic, say 150 miles.  maybe another 100 miles since then.

carbs are mikuni vm30's with k&n filters.

jetting:

150 mains
6F4 needles, leanest clip settings
P-5 #159 needle jets
air correction jets removed (in effect, a bigger jet than the 2.0's i had in there before)
25 pilots
2.5 throttle slide cutaway