Topic: cb500 white smoke back through airbox!

[buckett]

Howdy!

Hope everyone's having a cool day.
I have a cb500, all stock except aftermarket 4 into 1 exhaust, that I've been ticking off maintenance procedures on, so far I have
 - adjusted valves
 - adjusted camchain
 - set point gap
 - set point timing with strobe
 - carb synched
 - new air filter

also of interest is that I'm 90% sure it is running lean as it has a 4 into 1 non stock and runs a little hot and pops and spits a little especially when decelerating in gear (not that I really know how hot it should be) and runs better on a warmer day.

Since the bike has been run it has always blown some white smoke back through the airbox at idle when it is reasonably hot after about 15 min of riding. This happens at idle, it isn't huge amounts but definitely not normal. It isn't coming from the cam cover breather tube (as I don't have it on at the moment). The smoke drifts up from under the seat and doesn't smell much like anything! It stops immediately when engine is cut and starts instantly when it is started again (only if already hot). pretty sure it isn't water as the bike is consistently kept garaged and surely would have all evaporated by now!

Is this just a symptom of leanness or does it indicate something more???

I do have a compression tester that I haven't utilised so maybe that will help?

thank you in advance to anyone who has some input!

EDIT: important detail is that previous owner had camshaft backward and the bike running with it like that, ie. right side on left, left side on right, and I had to flip it over to the correct way (noticed as tacho was dead!)

[dave500]

id re check the ignition timing first,sounds like inlet valves are leaking slightly?

[buckett]

I did the timing yesterday and lined up the mark to within 1mm (almost fully adjusted the plate around one way) but maybe the engine wasn't hot enough? didn't do it cold but was a bit lazy waiting for it to warm up. will recheck for sure

cool beans thanks dave

[HondaMan]

Check your compression, for sure. If one cylinder is/was lower than the others by more than 10 PSI, and then the carbs were vacuum balanced on top of that, then that cylinder will spit back into the intake tract on every revolution.

The pipe will not affect your jetting significantly until 6000+ RPM, but the air filter can: what type of filter did you install? For the jetting issue at high RPM, try adjusting the jet needle's clip (move the needle a notch up), but NOT until you've verified the compression, or it will just cause confusion.

If the intake valve(s) is leaking, this will cause the symptoms you describe. This leak can come from a crudded-up valve, a burned valve, or a worn-out valve guide that doesn't let the valve seal quickly when the cam closes it. If you suspect dirty valves or worn guides, then increase the valve lash clearance to .004" to .005" and run that way for a while to see if things start to improve. If you suspect cruddy valve faces (often caused from sitting for long periods of time, as the valve sat open to moist air over time), then you can try an old trick, which helps clean them: first, remove the airbox (so you can access the openings of the carbs) and run the engine for a good long time to heat it up (30 minutes or more). Then, with it running, squirt in some water to one cylinder at a time, holding the engine at 2000-3000 RPM as steadily as you can. It only takes one or two squirts, less than 1/2 ounce total water, to shock the valve face and make it release the bits that might be stuck to it. Easy to say: hard to do! I've used a detergent bottle (small one) to squirt the water, still is hard to get it in. Don't make it real big squirts, as this can hydraulically lock the cylinder, instantly killing the engine:that can be real hard on the pistons, even rods. Some folks have done it with a squirt gun, but this isn't much water so it doesn't always work out very well.

If all else fails, get a top end gasket kit and pull off the head, and take a look: leaking valves will appear clean around their edges where the gases are moving back & forth (instead of one direction), which slowly washes off the carbon coating.

[buckett]

Air filter is stock OEM honda.

Could this be some residual damage from the P.O. having the camshaft installed the wrong way?! (probably should have included this in the original details)

will get on to timing and compression checks asap too.

thank you , thanks, thank you !!!!

[dave500]

wrong way?please explain!if it was"180 THE WRONG WAY"itll be ok,but if it was mistimed a few teeth and its had a valve hit a piston one might be slightly bent?

[buckett]

wrong way?please explain!if it was"180 THE WRONG WAY"itll be ok,but if it was mistimed a few teeth and its had a valve hit a piston one might be slightly bent?

yup 180 so it should be ok then?


http://forums.sohc4.net/index.php?topic=118147.msg1334886#msg1334886

[dave500]

yep,even without taking the cam out just rotate the engine a further 360 degrees back to the 1/4 timing tdc mark,the cam will now be at its proper timing spot,YOU CANNOT HAVE THESE CAMS 180 OUT FULL STOP!!you cant have any cam 180 out,they spin at half crank speed,so for every 360 crank the cam does 180,time and set your cam by the book,,now rotate your crank 360 back to the 1/4 timing tdc mark and look at the cam slot,its now facing backwards,,WHOA!!my cams 180 out???


i just read that link to your older post,,,no no no,not that sort of 180 #$%*ing out man!!im talking timed incorrectly not put in arse about for #$%*s sake!!no #$%*ing wonder you have #$%* going on,go and shoot the po.

i now call a bent valve?

[buckett]

yep,even without taking the cam out just rotate the engine a further 360 degrees back to the 1/4 timing tdc mark,the cam will now be at its proper timing spot,YOU CANNOT HAVE THESE CAMS 180 OUT FULL STOP!!you cant have any cam 180 out,they spin at half crank speed,so for every 360 crank the cam does 180,time and set your cam by the book,,now rotate your crank 360 back to the 1/4 timing tdc mark and look at the cam slot,its now facing backwards,,WHOA!!my cams 180 out???


i just read that link to your older post,,,no no no,not that sort of 180 #$%*ing out man!!im talking timed incorrectly not put in arse about for #$%*s sake!!no #$%*ing wonder you have #$%* going on,go and shoot the po.

i now call a bent valve?

Oh ok.

I flipped that over to the right wau when I posted the previous thread!!! I'm about 95% sure I've got everything the right way now otherwise it would be pretty obvious by the sound I assume??

So that valve damage seems like the likely culprit considering. mmm

nightmare bike but jeeez I'm learning a lot

[dave500]

run a compression test and see what you find,if ones much lower than the rest the heads coming off i think?

[buckett]

Ok

so compression appears to be 115psi +/- 5 psi on all four.

this is low overall but a good sign that none of them are different no? an intake valve leak as Hondaman describes would mean lower compression on one right?

also I think my reading might be a little low overall because.... well how do you get the compression tester tight into the spark plug holes with a hot engine???

thanks for your help so far guys

[dave500]

use a screw in one.

[Deltarider]

cb500 white smoke back through airbox!

Habemus papam?

[bryanj]

If you have no tube on the top cover breather outlet(normaly hangs down behind engine) any vapour, which would probably be white could easily appear from under the seat

[buckett]

use a screw in one.

haha yeah yeah but I mean do you just turn the tube until it won't go anymore (not very tight at all)?

edit: ooooh I am a special child. adapter in first, then tube, then guage derrr. will retest tomorrow

If you have no tube on the top cover breather outlet(normaly hangs down behind engine) any vapour, which would probably be white could easily appear from under the seat

got down on hands and knees and had a reall good look and pretty sure it wasn't from the breather but I'll attach my new tube tomorrow and see how it goes, thanks for the suggestion!

[buckett]

cb500 white smoke back through airbox!

Habemus papam?

had to google this. very clever hahah

[70CB750]

haha yeah yeah but I mean do you just turn the tube until it won't go anymore (not very tight at all)?

I used silicon plumbers tape to seal the thread on a tester, but you can just slip an o-ring on the adapter and tighten it down.

[buckett]

SO turns out the breather tube was it, put it on and routed it and all clear.

I took all the care in the world to visually verify as I suspected this but DAMN IT. pretty silly of me I'm really sorry if anyone feels like I've wasted their time, thank you very much for everyone's help!

[bryanj]

No waste at all mate just more for the aging grey cells to remember, now who am i?