Author Topic: Smoke out of the crankcase breather (cb400f) (Read 5868 times)

Polio · « **on:** March 17, 2016, 03:07:17 AM »

Hello,
I've been using this bike for sometime now even tough I never quite managed to solve the rich mix problem (3 out of 4 plugs get still covered in black soot).

Now a few weeks ago I had some problems starting it and when I managed to get it going fuel was coming out of the exhaust,
I found out the airfilter was completely soaked, so I ordered a new one, but I also got the idea to disconnect the crankcase breather to see if that was the cause of the soaking.

After using the bike for a while I noticed smoke coming out of it, and I'm pretty positive is not just condensation because it doesn't disappear at any point and it's kinda influenced by the throttle.
I also found out that the gasket of the valve cover is broken in a few spots, and probably has been for some time but I didn't realize it because the oil and the smoke were being directed to the airbox.
What could be the cause of this?

Before realizing the airfilter was responsible for the fuel out of the exhaust I tried to clean the carbs and lower a bit the float level (really a fraction of an hair) on the 3 carbs that are still giving me soot on the spark plugs, and apparently they're running even richer than before (!?) shooting a regular puff of black smoke out everytime I rev it up, am I misunderstanding how float valves work?

flybox1 · « **Reply #1 on:** March 17, 2016, 09:42:39 AM »

Quote from: Polio on March 17, 2016, 03:07:17 AM

Hello,
I've been using this bike for sometime now even tough I never quite managed to solve the rich mix problem (3 out of 4 plugs get still covered in black soot). Tell us what of the 3000mi maintenance items you have or have not completed

Now a few weeks ago I had some problems starting it and when I managed to get it going fuel was coming out of the exhaust, more likely it is condensation which smells like burnt fuel
I found out the airfilter was completely soaked, so I ordered a new one, but I also got the idea to disconnect the crankcase breather to see if that was the cause of the soaking. not likely, the moisture and vapor are separated in the unit below the battery. vapor is recycled into the airbox, moisture collects and drains out the bottom. service teh separator unit and clear out the drain tube

After using the bike for a while I noticed smoke coming out of it, and I'm pretty positive is not just condensation because it doesn't disappear at any point and it's kinda influenced by the throttle.
I also found out that the gasket of the valve cover is broken in a few spots, probably will want to replace it at some point if it is leaking oil bad enough and probably has been for some time but I didn't realize it because the oil and the smoke were being directed to the airbox.
What could be the cause of this? Its normal crankcase vapor. return all the hoses to their intended separator, after you clean it

Before realizing the airfilter was responsible for the fuel out of the exhaust I tried to clean the carbs and lower a bit the float level (really a fraction of an hair) on the 3 carbs that are still giving me soot on the spark plugs, and apparently they're running even richer than before (!?) shooting a regular puff of black smoke out everytime I rev it up, am I misunderstanding how float valves work? please let us know what jet size and brand you have in the bike, did you clean the emulsion tube under the press in main jet? screw in pilot jet holes clean? what height did you set your floats at? if youve verified your fuel level using the clear tube method, exhaust type, air screw(mixture) setting

Polio · « **Reply #2 on:** March 17, 2016, 10:33:24 AM »

I've done most of the engine related maintenance around 1000 miles ago, valve clearance, oil change
(didn't replace the oil filer this time because the bolt is stuck, I'll look into that next oil change),
cam chain tension.

I'm positive the liquid coming out of the exhaust was fuel, because it would stop as soon as I removed the air filter and start again when placed it back.
I actually just replaced the airfilter with a new one and it's working much better, the mixture feels much better now and it's not making as much black smoke while revving the engine as before.
I'll try to check if the drain tube is clogged.

The jets are not oem honda but still the standard size, (can see them here http://forums.sohc4.net/index.php/topic,150035.msg1712117.html#msg1712117).
I cleaned jets and needles when I tried to change a bit the float level (set at 21mm) a couple of days ago,
I've read that the float should be set so that it's just slightly touching the valve spring, but I had to set it so that the pin is almost halfway trough its travel.
The exhaust is a marving reproduction.

flybox1 · « **Reply #3 on:** March 17, 2016, 10:46:43 AM »

Quote from: Polio on March 17, 2016, 10:33:24 AM

I've done most of the engine related maintenance around 1000 miles ago, valve clearance, oil change
(didn't replace the oil filer this time because the bolt is stuck, I'll look into that next oil change),
cam chain tension. Timing? Vacuum sync of the carbs?

I'm positive the liquid coming out of the exhaust was fuel, because it would stop as soon as I removed the air filter and start again when placed it back. it died because you leaned it out by taking the filter off. its condensation, not fuel. make a coin sized puddle and put a flame to it
I actually just replaced the airfilter with a new one and it's working much better, the mixture feels much better now and it's not making as much black smoke while revving the engine as before.
I'll try to check if the drain tube is clogged.

The jets are not oem honda but still the standard size, (can see them here http://forums.sohc4.net/index.php/topic,150035.msg1712117.html#msg1712117).
no mention of the emulsion tube under the main jet or the pilot jet holes/cleanliness...what are your air screws set at?
I cleaned jets and needles when I tried to change a bit the float level (set at 21mm) a couple of days ago.
I've read that the float should be set so that it's just slightly touching the valve spring, but I had to set it so that the pin is almost halfway trough its travel. float height is set when the float tang is resting against the float valve pin. you need to complete a clear tube test to see how well youve set the float height. i suspect its still incorrect here.
The exhaust is a marving reproduction. with aftermarket pipes, your jetting will need to be adjusted. stock jets will not work here.

flybox1 · « **Reply #4 on:** March 17, 2016, 10:58:54 AM »

I think the first thing you need to do is verify fuel level in your bowls is correct. adjust your floats as needed.
Then proceed with an idle plug chop with new plugs to have a look at idle mixture, adjust your air screw to accommodate, or, change jet sizes if it can properly be adjusted for a good mixture.
then, a vacuum sync.

flybox1 · « **Reply #5 on:** March 17, 2016, 11:03:03 AM »

For my 350F, i used aftermarket float valves and seats.
Because of the different internal spring pressure and pin length, i had to go from stock 21mm to 24mm on my float height to get the proper fuel level.
I suspect your fuel level is off because of the same reason.

Polio · « **Reply #6 on:** March 17, 2016, 11:20:01 AM »

I meant the leak would stop when the air filter was removed, not the bike, the engine was still running trough that.

I need to take the bike to a mech for a vacuum sync because I don't have a gauge, but the last time I did it the mech wasn't able to solve the rich mixture problem either.

I cleaned emulsion tubes the same moment I cleaned the jets, I cleaned pretty much everything inside the carbs,
the air screws are set 1 1/2 turns out, set by the mechanic that sync'd the carbs the last time.

The exhaust is one of the most common replica around of the original, and supposedly shouldn't need rejetting as far as I'm told.

Quote from: flybox1 on March 17, 2016, 10:58:54 AM

I think the first thing you need to do is verify fuel level in your bowls is correct. adjust your floats as needed.
Then proceed with an idle plug chop

I'll try checking the fuel level with the clear tube method, the line should be 3-4mm from the conjunction between the carb and the bowl right?

Quote from: flybox1 on March 17, 2016, 11:03:03 AM

For my 350F, i used aftermarket float valves and seats.

That could be the reason, I recently found a set of OEM float valve set.
Bit pricey but what the hell if that's the problem I should go with it.

flybox1 · « **Reply #7 on:** March 17, 2016, 11:32:30 AM »

you need to get the fuel level correct before attempting to adjust the air screw to get the mixture correct.
yes 3-4mm below the top of the bowl is ideal.
no need to change float valves....use what you have and adjust your float height get the fuel level correct.
the mm's you set the float height is irrelevant. correct fuel level is the goal.

Polio · « **Reply #8 on:** March 17, 2016, 11:43:07 AM »

I'll be sure to do that,
one thing I'm not sure about, to check the fuel level of the central carbs can I just use a longer tube and use the external carbs bowl as reference?

flybox1 · « **Reply #9 on:** March 17, 2016, 11:47:36 AM »

take the carbs off the bike and do it on the bench, then its easier and quicker to make small float adjustments, test. retest.
no need to take carbs off and on the bike so many times.
make a stand for the carbs so they are level, and rig up an aux fuel source, or put your tank just higher than the area you have your carbs on

Polio · « **Reply #10 on:** March 18, 2016, 01:13:51 PM »

I checked the fuel level in the bowls, it seems to be in spec honestly... maybe even a mm lower than 3-4mm,
so I don't think that's what's causing the bike to run rich.

flybox1 · « **Reply #11 on:** March 18, 2016, 02:50:48 PM »

Those look good, so, now, warm up the bike.
Remove your plugs and put in a NEW out of the box, set of NGK D8EA's , and get it idling again.
No revving, blipping of the throttle.
Set a box fan aimed at the front of the engine, and let it idle for 4-5 more minutes.
Pull the plugs back out, and line them up 1-2-3-4
Take a picture. We need to see the plugs at this angle and up close.

Polio · « **Reply #12 on:** March 19, 2016, 05:02:27 AM »

I have to say I expected a completely different result from this.
Here they are (order 1-2-3-4).
So this should indicate that something is wrong with the idle jets?
http://imgur.com/a/RVMZF (wouldn't let me post them here)

Also a pic to show just how much smoke is coming out of the breather.

Polio · « **Reply #13 on:** March 21, 2016, 08:58:13 AM »

I tried using the bike for a bit today, it feels jerky and I can feel both symptoms of lean carburation and rich carburation,
jerkyness (specially under 4k), black smoke when I open the throttle and overall poor acceleration.

Am I running with two carbs too lean and two too rich?

flybox1 · « **Reply #14 on:** March 21, 2016, 09:04:44 AM »

#1 is perfect.
#2 - RICH turn air screw OUT 1/2 turn
#3 - lean, turn air screw IN 1/4 turn
#4 - Rich, turn air screw OUT 1/2 turn

Put in a new set of plugs in cyls 2/3/4 and perform idle chop again.
Dont ride, dont blip the throttle. Just let it idle under a fan 4-5 minutes.
Pull the plugs and post pictures.
Paste your imgur link in the thread field, highlight it, and then hit the mona-lisa looking icon above the emojis

Tim2005 · « **Reply #15 on:** March 21, 2016, 09:53:46 AM »

What mileage has the motor done, and/or have you carried out a compression test?

flybox1 · « **Reply #16 on:** March 21, 2016, 10:15:16 AM »

OK...I went back and re-read this thread and your original thread.
if ALL mixture screws are/were turned out 1 1/2 turns you or your mechanic. (2 turns out is at the max of its tuning range)
AND, all your jets are NOT Keihins
AND, all your fuel levels are equal/correct
adjusting your air screws might be enough, but I suspect the aftermarket jets are inconsistent enough to give you your tuning issues.

You'll need new mains and screw-in pilots, and the mains will need OEM orings on them so as to not let unwanted fuel to pass.

Polio · « **Reply #17 on:** March 21, 2016, 10:46:29 AM »

Quote from: Tim2005 on March 21, 2016, 09:53:46 AM

What mileage has the motor done, and/or have you carried out a compression test?

25k miles, but I suspect it has been rolled back at some point, so it's hard to tell.
No I didn't, not with a psi gauge at least, I just tried to crank the engine with 1 plugs at at time.

Quote from: flybox1 on March 21, 2016, 09:04:44 AM

#1 is perfect.
#2 - RICH turn air screw OUT 1/2 turn
#3 - lean, turn air screw IN 1/4 turn
#4 - Rich, turn air screw OUT 1/2 turn

I had to use the previous set of plugs for the moment but it sounds much, much better already.
In 12-15 hours I'm gonna buy some more plugs to test it.

Quote from: flybox1 on March 21, 2016, 10:15:16 AM

You'll need new mains and screw-in pilots, and the mains will need OEM orings on them so as to not let unwanted fuel to pass.

I might have screwed up the fuel level the last time, probably lowered it by half a mm (on the 3 carbs that give rich/lean readings).
I suppose right now I'm mounting a set of keyster, and with aftermarket jets seems to be trying to win the lottery.
Is there a manufacturer you could suggest me? I saw somebody in this forum talking about jetrus.com

flybox1 · « **Reply #18 on:** March 21, 2016, 10:58:58 AM »

+1 for jetsrus.com
I shop there, first.

Polio · « **Reply #19 on:** March 22, 2016, 09:22:16 AM »

I went for a ride this morning to test the current air setting and to buy new plugs,
the bike was idling fine but still stumbling above 2-3k rpm.

I tough it would have been a good idea to reset the fuel level as it was before I touched it,
(only carbs N°2-3-4), but after the plug test I kinda regret doing it.

These are the plugs with the current air screw setting, and after having changed the fuel level.
I noticed the bike was idling higher than usual this time, closer to 1.8k rpm.

N°2
http://imgur.com/jbjSNlh

N°3
http://imgur.com/tL4uiWt

N°4
http://imgur.com/RgqVVQD

(still wouldn't let me post them directly for some reason)

flybox1 · « **Reply #20 on:** March 22, 2016, 05:49:34 PM »

all of those now are slightly lean. air screws in 1/8 turn.
turn your idle down with the idle set screw. If your idle set screw is all the way out, and it still idles high, your slide heights are too varied and not allowing them to close all the way.
start over with a bench sync after you set the sync screws at mid of their adjustment range.

Polio · « **Reply #21 on:** March 23, 2016, 11:04:21 AM »

Hell of a day,

Tried 1/8 in on the three air screw, and it was still too lean so I turned them in another 1/8 (1/4 totally) and it was still to lean,
the engine was still banging and making noises.

Sucked it up and tried to change the fuel level again, just a tiny sliver (turned 1/4 out the air screws before doing it).

Now they were a tiny bit richer, and I think I got the right setting on the fourth carburetor, the number 2 and 3 appear to be still too lean.
I'll have to buy another set of plugs tomorrow and start this damn carousel again.

On top of that I feel like the bike is running much worse now, no acceleration, jerky as hell, and when idling it seems to have regular "peaks".

Wish there was a reset button on these carbs.

flybox1 · « **Reply #22 on:** March 23, 2016, 11:48:03 AM »

I really would stop and wait to do any more fine adjustments until you get new Keihin main and pilot jets in there.
you're chasing your tail with these aftermarket jets.

Polio · « **Reply #23 on:** March 23, 2016, 12:21:14 PM »

I should get the set of NOS original honda jets I ordered in couple of days.
I found them from a local seller, buying them from jetrus would have costed just the same but would have taken a week or so.

Man, if you ever cross the Atlantic remember there's a guy that owes you beer here.

flybox1 · « **Reply #24 on:** March 23, 2016, 12:26:28 PM »

Excellent!

Good on you for getting the right stuff for your bike.
In the meantime....do whatever you can to ready those carbs (and the rest of the bike) for the new jets.
Clean, accurate bench sync, bowl fuel levels, etc.
Once running, all you should have to do is get the mixture screws dialed in and then a vacuum sync.

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Author Topic: Smoke out of the crankcase breather (cb400f) (Read 5868 times)