Author Topic: exhaust smoke leaking past valve seal?  (Read 546 times)

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Offline setdog

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exhaust smoke leaking past valve seal?
« on: May 07, 2013, 01:08:49 PM »
75 cb750

So...after a brief ride today, I noticed a bit of smoke, smelled like exhaust, coming up from around
The air box area.  I don't have a hose on the breather vent in the head, so I've decided the smoke is
Coming from the vent, and not from the air box as I initially thought.

Assuming I'm correct and the smoke is coming from the head vent, this leads me to
believe my valve seals are shot.

~40 year old valve seals...what are the odds there are performing as they should and the
The problem lies elsewhere?

Like rings?

The words tear down...are starting...no...must not let...arghhh...they're getting bigger and bigger
And starting to flash.

« Last Edit: May 07, 2013, 01:14:54 PM by setdog »
My toolbox consists mainly of hammers.

76 CB 200T. (sold)
75 CB 750 K5. (sold)
74 CB 750 K4. (current rider)
73 CB 750 K3. (build)

https://www.youtube.com/user/setdog100

Offline flybox1

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Re: exhaust smoke leaking past valve seal?
« Reply #1 on: May 07, 2013, 01:23:24 PM »
thats the vent from the valve cover. vapor is normal.
the hose should attach to the filter unit between the rear fender and case, under your battery.
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline setdog

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Re: exhaust smoke leaking past valve seal?
« Reply #2 on: May 07, 2013, 01:28:34 PM »
thats the vent from the valve cover. vapor is normal.
the hose should attach to the filter unit between the rear fender and case, under your battery.

I hope its vapor...i tried sniffing it... but that proved to be highly inconclusive. not very scientific...Ill get a hose on it asap. 
My toolbox consists mainly of hammers.

76 CB 200T. (sold)
75 CB 750 K5. (sold)
74 CB 750 K4. (current rider)
73 CB 750 K3. (build)

https://www.youtube.com/user/setdog100

Offline flybox1

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Re: exhaust smoke leaking past valve seal?
« Reply #3 on: May 07, 2013, 01:37:02 PM »
dont sniff that stuff  :o
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"