Excessive head pressure. Breather Restriction

[sdaigle240]

65 cb305 basket case.

When i shut the engine off, the breather tube off the head hisses air out for 10-15 seconds.

if you try to blow back into the tube, its like filling a balloon. it gets harder to blow and when you release all that air comes back out the tube. the tube itself is clear.

Oil is passing by my points seal - admittedly Ive yet to replace it.

Oil is passing out my tach cable. the o ring is fine, and that parts seals. the oil is going up the housing and then leaking from where the cable housing meets the threaded head of the cable.

Clearly i have a problem i need to address before i go making things worse. Are there any suspect things i can be investigating prior to a complete tear down? My first hope was that i clogged the breather nipple with junk while the engine was upside down for a few weeks but that doesn't appear to be the case.
and i just got this thing back together after the upside down shift drum bracket from the previous owner. oh well.

As always, thank you so much for your input, all.

-Steve

[G-Man]

Steve

Any smoke coming out?

If air is coming out it cannot be blocked.....

As that is the breather, if you are trying to blow air into it then you are blowing into an otherwise sealed space.....

Is air blowing out when the engine is running? Try putting your finger over the hose.

How is the compression for each of the cylinders? How long has the engine been standing? You may have stuck rings.

G

[sdaigle240]

G, thank you.

There is no smoke coming out the breather.

I poorly assumed its like a car with a timing chain where the crank case and valve cover are open to each other and you have a breather on the case and a breather on the valve cover. I was next going to look for a breather on the case. Sounds that I'm completely off. If it has only one opening that makes sense for what's happening when I blow in the tube. Oops.

I will get it back together to test the breather while running. I'd be surprised if it wasn't passing air while in operation but will check.

Can only sem to find my leakdown check at the moment as I just moved but I know this is critical and need to be checked before going to far. Will report back on compression numbers.

I bought the bike about 5 years ago and suspect it sat a good bit longer before hand. I just got it running. Someone else was also mentioning to me that the compression ring could be leaking while the oil rings still doing its job... Allowing excessive blow by to make its way up to the head. I guess well see what the compression says.

[sdaigle240]

ok...

while running the tube pushes out a little air. not much.

when you shut the engine off and the tube hisses, its actually inhaling air not exhausting it. the tube that was on there was too small so it further highlighted the hiss and restricted flow. with the new tube on there the hiss only lasts 2/3rds as long when shut off. its a very obvious noise and my dream doesnt make this noise if i recall correctly.

Perhaps false alarm. could be the points seal is just plain bad and the garbage tach cable just plain leaks. will be replacing both and checking the compression. thanks.

[sdaigle240]

Replaced the points seal, havent borrowed a compression tester yet. the bike runs strong though.

I still have oil leaking out the tach cable. New cable, new o ring, ive got the washer in the correct spot and it still leaks. it does not leak past the o ring. its leaking internally, up the inside of the cable and then out the threads.

[PhilD]

Had a similar problem recently, solved when I realised I had put the cable oil seal in the wrong way round DOH ! Control side should of course face down towards tacho drive. Worth a quick check. Standard 7x14x4mm rotary seals work well if you need a replacement.
PhilD

[sdaigle240]

thank you phil i will have a look.