Topic: CB350F carb + breather smokes

[Greencb350f]

My cb350f starts smoking out the breather hose after running it for a wile. What are some of the causes?

Plus I rebuilt the carbs and have been having a problem after running it around the idle hangs high. If I adjust the idle back down then it will start idling too low. Any ideas.

Engine has 14,975miles

[TwoTired]

If the smoke is white, it's water vapor.  You want to thoroughly heat the motor until that stops.

[carnivorous chicken]

My cb350f starts smoking out the breather hose after running it for a wile. What are some of the causes?

Plus I rebuilt the carbs and have been having a problem after running it around the idle hangs high. If I adjust the idle back down then it will start idling too low. Any ideas.

Engine has 14,975miles

For your carb issue -- have you synced your carbs? Checked for air leaks? checked float height? Made sure carbs are clean, including jets? Have you checked your timing?

[markreimer]

White breather smoke is almost certainly moisture burning off. It can take a surprisingly long time to burn it all out if you’re normally doing short trips and/or live somewhere with cool overnight temps. My 750 takes up to an hour of highway riding or more to really burn out all the condensation


Sent from my iPhone using Tapatalk

[Greencb350f]

If the smoke is white, it's water vapor.  You want to thoroughly heat the motor until that stops.

I'm pretty sure it's blue and smells petty bad.  The bike looked to have been sitting for a long time.

My cb350f starts smoking out the breather hose after running it for a wile. What are some of the causes?

Plus I rebuilt the carbs and have been having a problem after running it around the idle hangs high. If I adjust the idle back down then it will start idling too low. Any ideas.

Engine has 14,975miles

For your carb issue -- have you synced your carbs? Checked for air leaks? checked float height? Made sure carbs are clean, including jets? Have you checked your timing?

I rebuilt the carbs with ebay carb kits. Cleaned them out.  Adjusted float height and used a drill bit to set the slides evenly as I could.  Haven't checked timing, and never used vaccum guages to sync carbs, not even sure if the gauges are for setting the mixture screws or just setting the height of the slides?? This is a gray area for me,  but I'd love to learn how.  I  sprayed starting fluid around the intakes to see if they are leaking but didn't notice anything.  How do you properly check for air leaks? Could someone point me to a reasonably priced carb sync guages on eBay?

Thanks for the help!

[TwoTired]

If the smoke is white, it's water vapor.  You want to thoroughly heat the motor until that stops.

I'm pretty sure it's blue and smells petty bad.  The bike looked to have been sitting for a long time.

I was being optimistic.

Smells bad like burnt oil?
Anyway blue smoke out the breather is never a good thing.  Almost certainly blow-by past the pistons/rings and filling the crankcase.  If it's bad enough, high RPM operation will pump the crankcase oil out the breather, usually onto the rear tire...  slippery, that.

There is a chance that some run time will re-seat stuck rings.  Otherwise, holes in pistons, burnt pistons, rusty cylinder walls, broken rings, seized rings, are all possibilities.

To save yourself grief and wasted time trying to tune and check engine mechanicals.  Do a compression check with a small engine comp tester.  Or better yet, a leak down tester which can tell you just what is leaking out the cylinder and where the pressure is going, by hearing the escaping air.

Cheers,

[carnivorous chicken]

I rebuilt the carbs with ebay carb kits. Cleaned them out.  Adjusted float height and used a drill bit to set the slides evenly as I could.  Haven't checked timing, and never used vaccum guages to sync carbs, not even sure if the gauges are for setting the mixture screws or just setting the height of the slides?? This is a gray area for me,  but I'd love to learn how.  I  sprayed starting fluid around the intakes to see if they are leaking but didn't notice anything.  How do you properly check for air leaks? Could someone point me to a reasonably priced carb sync guages on eBay?

Thanks for the help!

OK -- hopefully you saved the original brass (jets, float valves if they were in good shape) when you rebuilt your carbs. Aftermarket brass can work OK, but the original keihin brass is better. You'll want a manometer (sync gauge) to dial in your carb sync (not the mixture screws) -- don't get a cheap Motion Pro one, spend the money for a Morgan Carbtune or if you can find one a mercury gauge. You'll need one. Sounds like you're air tight, although be careful with starting fluid.

Do you have a manual? IF not, get one, and read it. You'll need to check your timing, your points, and your valves.

IF, however, you have a compression issue (do a compression test as TwoTired mentioned) you're not going to be able to tune it properly. But -- if it's rings that need to re-seat, give it some time and you might as well work on the tuning.

[Greencb350f]

If the smoke is white, it's water vapor.  You want to thoroughly heat the motor until that stops.

I'm pretty sure it's blue and smells petty bad.  The bike looked to have been sitting for a long time.

I was being optimistic.

Smells bad like burnt oil?
Anyway blue smoke out the breather is never a good thing.  Almost certainly blow-by past the pistons/rings and filling the crankcase.  If it's bad enough, high RPM operation will pump the crankcase oil out the breather, usually onto the rear tire...  slippery, that.

There is a chance that some run time will re-seat stuck rings.  Otherwise, holes in pistons, burnt pistons, rusty cylinder walls, broken rings, seized rings, are all possibilities.

To save yourself grief and wasted time trying to tune and check engine mechanicals.  Do a compression check with a small engine comp tester.  Or better yet, a leak down tester which can tell you just what is leaking out the cylinder and where the pressure is going, by hearing the escaping air.

Cheers,

Yes it smells of burnt oil.  I did a compression test  a couple of weeks ago when I got out running and it was 120's and 115's.

How do you do a leak down test?

Chris

[Greencb350f]

I rebuilt the carbs with ebay carb kits. Cleaned them out.  Adjusted float height and used a drill bit to set the slides evenly as I could.  Haven't checked timing, and never used vaccum guages to sync carbs, not even sure if the gauges are for setting the mixture screws or just setting the height of the slides?? This is a gray area for me,  but I'd love to learn how.  I  sprayed starting fluid around the intakes to see if they are leaking but didn't notice anything.  How do you properly check for air leaks? Could someone point me to a reasonably priced carb sync guages on eBay?

Thanks for the help!

OK -- hopefully you saved the original brass (jets, float valves if they were in good shape) when you rebuilt your carbs. Aftermarket brass can work OK, but the original keihin brass is better. You'll want a manometer (sync gauge) to dial in your carb sync (not the mixture screws) -- don't get a cheap Motion Pro one, spend the money for a Morgan Carbtune or if you can find one a mercury gauge. You'll need one. Sounds like you're air tight, although be careful with starting fluid.

Do you have a manual? IF not, get one, and read it. You'll need to check your timing, your points, and your valves.

IF, however, you have a compression issue (do a compression test as TwoTired mentioned) you're not going to be able to tune it properly. But -- if it's rings that need to re-seat, give it some time and you might as well work on the tuning.

I saved all the carb parts, however all the Orings were shot on the seat and jet. The springs seem weak on the needles (at least compared to the new seats) I don't know if that's a problem?  I tried to use the new Orings with the new carb kit but they won't fit the old parts. I don't know where you can get the proper Orings at.

How do you properly adjust the mixture screws then?

I have a Climers book if it's good enough.

So let me get this straight if I understand correctly, the carb sync guages are to only fine tune the slides inside the carbs (by making all 4 even in height or how much air they are letting in)  by ajusting them on top of the carbs correct?

Chris

[Greencb350f]

Will this work for what i need?  https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F132011656301

Thanks
Chris

[Greencb350f]

If the smoke is white, it's water vapor.  You want to thoroughly heat the motor until that stops.

I'm pretty sure it's blue and smells petty bad.  The bike looked to have been sitting for a long time.

I was being optimistic.

I hold onto hope till the bitter end even though I know deep down I'm beating a dead horse.

Wouldn't the engine smoke out the exhaust too if the rings were shot?

[evinrude7]

chris, ride it and tune it, ride it and tune it.  that's my advice if it's a bike that sat for a long time and you recently acquired it.   

get a honda shop manual and the owners manual.  here's the shop manual.  i can't seem to locate the owners manual http://manuals.sohc4.net/cb350/service_manual/SM350400_1.pdf  http://manuals.sohc4.net/cb350/service_manual/SM350400_2.pdf

perform the 3000 mile maintenance schedule.  valve adjust, cam chain, points, timing.  make sure your float heights are correct using the clear tube method.  make sure you have no air leaks in carb boots.  carnivorous chicken and tt mentioned previously to do this work and possibly you'll have success in re-seating stuck rings.  change your oil as well.  wet clutch compatible oil.  be patient with this work.  it will take time, trial and error. 

don't worry about vacuum sync right now.  that will be last once you get everything else right and if your leaks settle down.

good luck.  some of the more experienced forum members will chime in with help on more complicated items.  if you are holding on to hope til the bitter end perform this work and see if it gets you some place.  my bike smoked a bit as well when i first got it.  it had sat for a few years, outside in the elements.  i got it running and toiled away on it for months riding and tuning, over and over again.  it's now a reliable bike that runs great.  have patience. 

[Greencb350f]

chris, ride it and tune it, ride it and tune it.  that's my advice if it's a bike that sat for a long time and you recently acquired it.   

get a honda shop manual and the owners manual.  here's the shop manual.  i can't seem to locate the owners manual http://manuals.sohc4.net/cb350/service_manual/SM350400_1.pdf  http://manuals.sohc4.net/cb350/service_manual/SM350400_2.pdf

perform the 3000 mile maintenance schedule.  valve adjust, cam chain, points, timing.  make sure your float heights are correct using the clear tube method.  make sure you have no air leaks in carb boots.  carnivorous chicken and tt mentioned previously to do this work and possibly you'll have success in re-seating stuck rings.  change your oil as well.  wet clutch compatible oil.  be patient with this work.  it will take time, trial and error. 

don't worry about vacuum sync right now.  that will be last once you get everything else right and if your leaks settle down.

good luck.  some of the more experienced forum members will chime in with help on more complicated items.  if you are holding on to hope til the bitter end perform this work and see if it gets you some place.  my bike smoked a bit as well when i first got it.  it had sat for a few years, outside in the elements.  i got it running and toiled away on it for months riding and tuning, over and over again.  it's now a reliable bike that runs great.  have patience.

Thanks for the help! Are you into Evinrude boat motors?

Chris

[Greencb350f]

I bought my bike back in 2000 after my CL350 ate the timing chain and cam ate into the head. When I bought the cb350f it would run but didn't have enough power to pull out. I gave up on it. Girlfriend said this year why don't you get that running.  So I just so happened to find a parts bike and bought it.  Put the motor on my bike and now I'm here. I probably should mention the oil filter was on wrong when I changed it. The guy had the spring and bushing flip flopped.  So I don't know how long it was run like that.  Would that starve the engine for oil?  It sounded good when I got it running but lately I have noticed the lower end sounds clunky at a idle. I wonder if the rods are knocking on the crank.  The clutch was stuck too, little rust pitts were holding it from moving. Got it free.


I have since put my old engine on the parts bike just too see if I could get it running and check the compression to see what was going on with that engine.  It only has 8,000 miles on it. And it was a pain to get running it didn't want to start. One coil seemed to not work on my bike, after running the engine for a wile the other coil seemed to fail too. So maybe that was the problem 17yrs ago.  But it runs now and even has the power to pull out. The compression on it is 120-125  little better than my smoking breather engine. I would think 120 isn't that good but then again I don't know what they should be.

[TwoTired]

Yes it smells of burnt oil.  I did a compression test  a couple of weeks ago when I got out running and it was 120's and 115's.

How do you do a leak down test?

Depending on the type of compression tester you used, those numbers are encouraging.  Car/truck comp testers gice lower than desired numbers when used on small engines, as they alter the compression ratio.


A leak down tester works with a compressor to supply a regulated amount of air into the engine cylinder (gauge one), when the piston is at the beginning of it's power stroke.
Gauge two reports the actual pressure maintained within the cylinder.

Leakages can me hear in the crankcase, exhaust, or intake, to note where the pressure is being lost.

Will this work for what i need?  https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F132011656301

Yes

Wouldn't the engine smoke out the exhaust too if the rings were shot?

Yes, it could.


A vacuum gauge sync tool measures the vacuum drawn by each cylinder through the carb.  An engine "should" draw the same for each cylinder.  If not, the slides can be positionally adjusted so that each cylinder can work to its optimum.

Your compression test showed that all cylinders are not equal.  Therefore, the carb slides will be adjusted differently to meet each cylinders demands.

The carb sync slide positions will only be exactly equal, if each cylinder is mechanically identical with all the others.  Rare that this occurs in old used/abused engines.

Cheers,

[TwoTired]

It sounded good when I got it running but lately I have noticed the lower end sounds clunky at a idle. I wonder if the rods are knocking on the crank. 

If the four cylinders do not provide even power power pulses at idle, the trans gears alternate contact face contact with the small change in crankrotational speed.   I call this gear clack.  If you don't know what to listen for, this could be interpreted as a rod or other engine knock.  These engines will gear clack at idle if the carbs are out of sync, among other reasons.

One thing to note is if the "clunky" changes when clutch pulled in.  Or if the "clunky" persists under trans operating loads.

Cheers,

[Greencb350f]

Yes it smells of burnt oil.  I did a compression test  a couple of weeks ago when I got out running and it was 120's and 115's.

How do you do a leak down test?

Depending on the type of compression tester you used, those numbers are encouraging.  Car/truck comp testers gice lower than desired numbers when used on small engines, as they alter the compression ratio.

I did not know there were differing kind. I just have one from a auto parts store.

Chris

[Greencb350f]

It sounded good when I got it running but lately I have noticed the lower end sounds clunky at a idle. I wonder if the rods are knocking on the crank. 

If the four cylinders do not provide even power power pulses at idle, the trans gears alternate contact face contact with the small change in crankrotational speed.   I call this gear clack.  If you don't know what to listen for, this could be interpreted as a rod or other engine knock.  These engines will gear clack at idle if the carbs are out of sync, among other reasons.

One thing to note is if the "clunky" changes when clutch pulled in.  Or if the "clunky" persists under trans operating loads.

Cheers,

Interesting! I'm pretty sure the clunky noise gets much less when the clutch lever is pulled in.  But I don't think it goes away completely until you rev it up to about 2grand.

[TwoTired]

Rod knock gets worse under drive train load.

"Gear Klack" goes away under drive train load.

I did not know there were differing kind. I just have one from a auto parts store.

The smaller the engine displacement, the more a larger engine tester will report lower compression results.  It matters where the check valve is in the apparatus.  If near the spark plug hole, little effect.  If at the gauge indicator, the entire volume of the connecting tube from cylinder to gauge, adds to the combustion chamber volume, altering the compression ratio, which is piston swept area volume to cylinder head volume.  Make the head volume larger and the compression ratio is reduced, equaling lower than accurate readings.

Small engine testers will have very narrow tubing to the gauge and/or the check valve right at the spark plug hole, so as not to alter the compression ratio too much.

I posted the math for this on this forum a few years ago.  Its in the FAQ.
http://forums.sohc4.net/index.php/topic,369.msg476032.html#msg476032

Cheers,

[Greencb350f]

Rod knock gets worse under drive train load.

"Gear Klack" goes away under drive train load.

I did not know there were differing kind. I just have one from a auto parts store.

The smaller the engine displacement, the more a larger engine tester will report lower compression results.  It matters where the check valve is in the apparatus.  If near the spark plug hole, little effect.  If at the gauge indicator, the entire volume of the connecting tube from cylinder to gauge, adds to the combustion chamber volume, altering the compression ratio, which is piston swept area volume to cylinder head volume.  Make the head volume larger and the compression ratio is reduced, equaling lower than accurate readings.

Small engine testers will have very narrow tubing to the gauge and/or the check valve right at the spark plug hole, so as not to alter the compression ratio too much.

I posted the math for this on this forum a few years ago.  Its in the FAQ.
http://forums.sohc4.net/index.php/topic,369.msg476032.html#msg476032

Cheers,

Mine has the check valve at the gauge. I opened the throttle all the way and cranked till the gauge  stopped moving,  maybe I did that wrong as well.
Under drive train load the clunking goes away.

I am loving all the information!  Thanks

Chris

[evinrude7]

chris, ride it and tune it, ride it and tune it.  that's my advice if it's a bike that sat for a long time and you recently acquired it.   

get a honda shop manual and the owners manual.  here's the shop manual.  i can't seem to locate the owners manual http://manuals.sohc4.net/cb350/service_manual/SM350400_1.pdf  http://manuals.sohc4.net/cb350/service_manual/SM350400_2.pdf

perform the 3000 mile maintenance schedule.  valve adjust, cam chain, points, timing.  make sure your float heights are correct using the clear tube method.  make sure you have no air leaks in carb boots.  carnivorous chicken and tt mentioned previously to do this work and possibly you'll have success in re-seating stuck rings.  change your oil as well.  wet clutch compatible oil.  be patient with this work.  it will take time, trial and error. 

don't worry about vacuum sync right now.  that will be last once you get everything else right and if your leaks settle down.

good luck.  some of the more experienced forum members will chime in with help on more complicated items.  if you are holding on to hope til the bitter end perform this work and see if it gets you some place.  my bike smoked a bit as well when i first got it.  it had sat for a few years, outside in the elements.  i got it running and toiled away on it for months riding and tuning, over and over again.  it's now a reliable bike that runs great.  have patience.

Thanks for the help! Are you into Evinrude boat motors?

Chris

no, it was a nickname one of my old drummers came up with back in 95.  many bands and years ago.  don't know why he chose that but it stuck.   

Rod knock gets worse under drive train load.

"Gear Klack" goes away under drive train load.

I did not know there were differing kind. I just have one from a auto parts store.

The smaller the engine displacement, the more a larger engine tester will report lower compression results.  It matters where the check valve is in the apparatus.  If near the spark plug hole, little effect.  If at the gauge indicator, the entire volume of the connecting tube from cylinder to gauge, adds to the combustion chamber volume, altering the compression ratio, which is piston swept area volume to cylinder head volume.  Make the head volume larger and the compression ratio is reduced, equaling lower than accurate readings.

Small engine testers will have very narrow tubing to the gauge and/or the check valve right at the spark plug hole, so as not to alter the compression ratio too much.

I posted the math for this on this forum a few years ago.  Its in the FAQ.
http://forums.sohc4.net/index.php/topic,369.msg476032.html#msg476032

Cheers,

tt, i wonder if he is describing loose cam chain that's noisey at idle.

[TwoTired]

tt, i wonder if he is describing loose cam chain that's noisey at idle.

I think those are usually described as ticking in the cylinder block, rather than a knock from down low.

But, then again printed descriptions of sounds can easily vary in precision.

Cheers,

[Greencb350f]

tt, i wonder if he is describing loose cam chain that's noisey at idle.

I think those are usually described as ticking in the cylinder block, rather than a knock from down low.

But, then again printed descriptions of sounds can easily vary in precision.

Cheers,

I've heard the cam chain noise when I tried to tighten it,  definitely a different noise.  I think he is right about gear klack.

Would K&L be a good carb kit as opposed to a junky eBay kit?

[TwoTired]

You normally just clean the brass bits.  You only need new rubber bits.

Aftermarket kits have poor quality control, leading to variances in part dimensions.  Original brass has a proven track record of working well when clean.
If you must replace, find Keihin parts.

Cheers,

[Greencb350f]

You normally just clean the brass bits.  You only need new rubber bits.

Aftermarket kits have poor quality control, leading to variances in part dimensions.  Original brass has a proven track record of working well when clean.
If you must replace, find Keihin parts.

Cheers,

Where do you get new O-rings for the Keihin parts? What's the best method to clean the brass?

Chris