Topic: White smoke from exhaust/breather, good compression, lean?

[jorwesflow]

Been dealing with a white smoke monster for a while. It starts happening mostly well after the bike is nice and hot. So it is not water vapor.

Top end was rebuilt about 2k miles ago. Compression looks good (although I'm not sure how 3 lost a little compression when wet):

Cylinder	Dry	Wet
1	129	130
2	125	132
3	130	126
4	126	125

I read somewhere that the white smoke could be a leanness symptom? Here's the plugs.

[ekpent]

 You've read it before but year, size and model of bike would be good to add to your description as well as some more specifics like air filter,exhaust pipe, maybe jetting etc..
 Have those spark plugs been run for 2K miles or recently installed ?

[jorwesflow]

You've read it before but year, size and model of bike would be good to add to your description as well as some more specifics like air filter,exhaust pipe, maybe jetting etc..
 Have those spark plugs been run for 2K miles or recently installed ?

I tend to forget that.

1977 CB550K, running uni pods, and a 4-1 MAC Canister exhaust.

Current jets are 42 slow, 112 main, needle one notch from highest setting. Air screws are 1/2 turn out (I can't remember with these carbs if air screws out is letting more air in or more fuel)

Plugs are at least 1k miles old.

[scottly]

I read somewhere that the white smoke could be a leanness symptom?

No, that is not correct.

[Deltarider]

Been dealing with a white smoke monster for a while. It starts happening mostly well after the bike is nice and hot. So it is not water vapor.

At what temperature would you expect water to become vapor then?

[jorwesflow]

Been dealing with a white smoke monster for a while. It starts happening mostly well after the bike is nice and hot. So it is not water vapor.

At what temperature would you expect water to become vapor then?

ha. well in my experience, the water vapor and condensation dripping out of the pipe stop after 5-10 minutes of riding, or a few miles.

The white smoke i have starts after at least 10 miles, and 20 minutes of riding, and doesn’t stop after that. i really see it when i come up to a stop light and my breather is fuming, and i look at my pipe and give a few revs and see some mild, but visible white clouds come out.

[PeWe]

Water needs 100C, at least a 20 minute ride to happen on my bikes.
A longer ride of 200km might help.
Smoke a little is normal.
EDIT: Above is about the breather only

If smoking from exhaust at start can be piston - bore clearance too big or leaking valve guide seals.
My CB750 K2 had extra smoke at startup due to piston-bore clearance.
Swapped cylinder and pistons with correct clearance, no smoke.

[Scott S]

 White-ish or blue smoke from the exhaust usually indicates that you're burning oil. Smoke from the breather is engine blow-by. Neither of these have anything to do with jetting.

 Black smoke from exhaust usually indicates a rich condition.

[PeWe]

Are those compression numbers really good? Full throttle when measured?
My CB750K2 had 140-150PSI with my previous oil smoking setup with too much clearance.

I think that the compression values can not differ that much to be healthy, CB500 or 750.

[markreimer]

My cb750 had a steady stream of white vapour coming out the breather tube until I was about 100km into a highway ride. Check your oil for that white schmoo floating on top or coating the filler cap. That’s all moisture. It would take a while to burn that all off. Then I’d park, engine cools down and after a few days it’s back to square one. It’s a good reason to take the bike on a proper long ride regularly


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[HondaMan]

You've read it before but year, size and model of bike would be good to add to your description as well as some more specifics like air filter,exhaust pipe, maybe jetting etc..
 Have those spark plugs been run for 2K miles or recently installed ?

I tend to forget that.

1977 CB550K, running uni pods, and a 4-1 MAC Canister exhaust.

Current jets are 42 slow, 112 main, needle one notch from highest setting. Air screws are 1/2 turn out (I can't remember with these carbs if air screws out is letting more air in or more fuel)

Plugs are at least 1k miles old.

Those are INCREDIBLY rich jets for a 550!
You haven't mentioned timing/spark: does the bike use points, or does it have a Dyna or similar ignition? If the springs on the spark advancer have not been trimmed back at least 1/2 turn (each) then the timing is advancing too soon to full. This causes spitback at the carbs, interrupting the flow [of air/fuel] to the carbs. If the timing is also advanced on top of that, it is worse, and then it becomes impossible to tune very well, because odd symptoms caused by these other things mask the real situation.

[jorwesflow]

Those are INCREDIBLY rich jets for a 550!
You haven't mentioned timing/spark: does the bike use points, or does it have a Dyna or similar ignition? If the springs on the spark advancer have not been trimmed back at least 1/2 turn (each) then the timing is advancing too soon to full. This causes spitback at the carbs, interrupting the flow [of air/fuel] to the carbs. If the timing is also advanced on top of that, it is worse, and then it becomes impossible to tune very well, because odd symptoms caused by these other things mask the real situation.

I'm using a Pamco ignition, and have another separate thread running on that http://forums.sohc4.net/index.php/topic,183334.0.html

And I'm definitely getting spitback at the carbs! I wasn't really sure what to call that, and if it was related or if I should start a different thread about it. But it's intermittent maybe once every 1-3 minutes a "spit" or two will occur. It's been a while since I've had this running well enough to go on long rides (separate elec issues with overcharging I'm working through—got a separate thread on that too! http://forums.sohc4.net/index.php/topic,176217.25.html )
But when I was running higher speeds on highways, this spitback would happen then as well, and cause a very quick loss of engine power. It was on my list of demons to exorcise.

But if the spitback is related to timing, then that helps narrow it down! So should the springs be trimmed? Seems like there isn't unanimity on that (I've read through this http://forums.sohc4.net/index.php/topic,131339.0.html)

But I know my advancer springs are definitely "sloppy". It was kind of a struggle getting the Pamco plate onto the advancer assembly because the springs kept falling off their little posts.

[scottly]

But I know my advancer springs are definitely "sloppy". It was kind of a struggle getting the Pamco plate onto the advancer assembly because the springs kept falling off their little posts.

Yes, your springs are definitely too loose if they fall off their little posts.

[PeWe]

Spitbacks is what my K6 had with sloppy springs advancing way too early.

If I'll get one more CB750, cut advancer springs will be mandatory as both my bikes have now.
I can not see any negative with harder springs, later advance.
K6: Very modified
K2: More or less stock
Both have a nice idle and smooth throttle roll-on/off.

[JerrodR]

White smoke is burning oil isent it? And if that's the case, bad rings?

[PeWe]

Can be worn bores, piston- bore clearance to high numbers.
If it is bore to next size, new pistons.
Cruzinimage sell oversize  pistons.
www.cruzinimage.net

[HondaMan]

But if the spitback is related to timing, then that helps narrow it down! So should the springs be trimmed? Seems like there isn't unanimity on that (I've read through this http://forums.sohc4.net/index.php/topic,131339.0.html)

But I know my advancer springs are definitely "sloppy". It was kind of a struggle getting the Pamco plate onto the advancer assembly because the springs kept falling off their little posts.

The 500/550 had too-soft springs when brand new. Even back in the 1970s we were trimming them back 1/2 to 1 full turn to get the bikes to settle down. You don't want full advance in that engine until at minimum 2500 RPM, and 3000 RPM is much better. On my own 500 that I had back when, I cut 1 off 1 spring and 1/2 of the other before it would act 'linearly' with the throttle and stop spitting at low 4th and 5th gear speeds. The slower advance did a lot for the low-end power, too, because it was not spitting the mix back at the carbs: it was actually taking it in.

After you get the timing right, I suspect you will start getting darker plugs. Then you may end up using smaller mainjets (and pilot jets), too.

[jorwesflow]

OK I cut about half a coil off each advancer spring, and then tried to reform the ends into something resembling when it had looked like. They're definitely noticeably tighter.

I fired it up and set the idle timing (with a strobe). Then tried to increase the throttle gradually to observe the advance. It was not very gradual at all. I would estimate that it seemed to not move much at all until 2500/3000 RPM at which point the advance almost suddenly jumped up. Is that what it's supposed to do? I was getting a lot of new popping from the exhaust as I increased the throttle, for whatever that's worth..

Did I shorten the springs too much? Reminder that I'm using a PAMCO ignition here.

[Maraakate]

The reasons you're stating is why I'm afraid to even play with those springs.  The book actually lists the proper spring tension which you could test with a spring tool from amazon.

With that said, has anyone ever called a supply house to find a spring of the right size and tension?  I find it amazing there is no aftermarket for this critical part that would costly a measly few dollars to get it back into spec.

[jorwesflow]

has anyone ever called a supply house to find a spring of the right size and tension?

I'm with you. I'd much rather just throw new springs on. Best I can find is to replace the whole assembly for $60. Not sure these springs would be worth $60 if they were made of gold.

https://4into1.com/spark-advancer-assembly-30220-323-154-honda-cb500k-550/

[Maraakate]

has anyone ever called a supply house to find a spring of the right size and tension?

I'm with you. I'd much rather just throw new springs on. Best I can find is to replace the whole assembly for $60. Not sure these springs would be worth $60 if they were made of gold.

https://4into1.com/spark-advancer-assembly-30220-323-154-honda-cb500k-550/

Yeah, and I wouldn't trust any aftermarket complete assembly crap from 4into1 anyways.

[jorwesflow]

Yeah, and I wouldn't trust any aftermarket complete assembly crap from 4into1 anyways.

The whole assembly, no. But at least the springs could be reliable?

[Maraakate]

Yeah, and I wouldn't trust any aftermarket complete assembly crap from 4into1 anyways.

The whole assembly, no. But at least the springs could be reliable?

They could be reliable, but are they the same size and same spring tension as the original?  You would have to buy them, measure them, then test the tension with a spring scale tool (not sure the exact name, you'll have to refer to the service manual).  If the part was $10 I'd chance it, but I'm not wasting $60 to find out the answer.

[PeWe]

Both my CB750 runs points with cut springs. Work really fine.
Full advance happen around 2600-2700 rpm.

My K6 got it soon 7 years ago when it had Pamco ignition.
Springs were so sloppy thst ignition was impossible to set. Full advance before 2000rpm.

Found Hondaman's mod to cut springs which fixed it.
Each spring cut 1/2 wound and reshaped to hook on.
Set ignition at Idle, full adv OK.

http://forums.sohc4.net/index.php/topic,131339.msg1464986.html#msg1464986

My K2 got it too.
If I should have 10 CB750 more, all will get that mod if using points, not waste time with ign problems.

Next mod is to make sure that all plugs are oriented towards In valve. Smoother throttle roll-on-off.
Indexing washers not needed, mark plugs and try them in which plug hole it match. You might need a box of 10 plugs to find matching ones. (Or less to avoid the plugs sitting 180 degrees away from In.)

Well worth it.

[jorwesflow]

Found Hondaman's mod to cut springs which fixed it.
Each spring cut 1/2 wound and reshaped to hook on.
Set ignition at Idle, full adv OK.

I did already cut the springs. So here's my question: should it be advancing gradually as you increase the throttle? because in my case, it seems to wait to advance and then jump forward more suddenly.

This means the springs are too tight/short right?