75 850 MK3 oiltank/breather

I am sure it has been answered before, but I cant seem to stop oil from leaking from the oil tank where the filler is.
I have tried changing the seal in the filler cap, checked the return hose clamp and the breather hose tube to the filler tower.
I have one of the sump plug breather valve setups, but this doesnt seem to have made any difference. I have a vague memory of a thread about connecting the breather to the oil tank vent outlet in the bulge forward of the filler, is this a good idea? any musings will be gratefully recieved!

I have to attach a reed breather to my MK111 return plumbings . Have a Mikes XS type . Stock. Ideas ?

Are you sure you're not overfilling the tank? Oil level checking should be performed after the engine's been running a bit, not before.

Not overfilling, I have oil cooler fitted which gives extra capacity so no to that...

Are you sure your tank breather pipe is clear?

Fast Eddie said:

Are you sure your tank breather pipe is clear?

Click to expand...

BINGO!

Probably a dauber wasp nest or a beetle bug up in there.

The Engine Breather goes to the oil tank and the Tank Breather gets vented to the atmosphere. If you have pressure build up in the oil tank then the oil tank breather is blocked and its lifting the oil cap. If you are sure the oil tank breather is clear make the oil cap tighter. Dont be afraid to use pump pliers on it to get a good seal. The turn til it clicks in place is simply not enough to stop oil from seeping out

When my breather clogged up there was so much pressure that it blew the hose off my oil filter bracket. Try running your bike for a couple of minutes and then quickly remove the oil tank cap. If it feels like it was under pressure ( I actually heard a pop) Eddie is probably steering you in the right direction.

Pete

Problem solved!
my own stupid fault... when I installed the beautiful sump plug breather valve and had to put in an adapter to change the hose diameter to the standard breather hose connection to the oil tank, I did not pay enough attention, probably cos I wanted to go for ride...
Anyway upon examination, I had not quite the right size and although hose clamps snugged up, there was a little crease...
anyway, new adapter thingy and a good blast and not a drop!
Thanks for all the suggestions..
Cheers

If you have the original emulsified oil separator in the oil tank vent line - clean it out, they fill and block for pastime, or just route the oil hose directly to the union that enters the air box and leave out the separator - I have been running like that for years and with the correct oil level you will not have a problem.

I was rummaging through my spares and found 2 oil separators, and cleaned and assembled 1 good complete one out of the pair.
However I have 35mm flatslide Keihin setup, so no where for oil to go...
ATM the vent hose is running down to back of chain guard with the vague hope that it will lube the chain...

You should put a smaller version of your air filter pods on that hose and let it rest on it's larger brothers. Venting that hose to the chain guard is not a good idea. You could lube the back tire as well as the chain.

I think you are right and I am gonna redo it....

I modified my separator by removing the bottom fitting and installing a barbed fitting. I then attached a hose going down the the ground. I use this as a drain for condensation. The center fitting still goes to the air box, this captures the vapors. You should be able to put a hole and grommet in the back of your air filter and connect this to the center fitting. I found that the original routing with the small hose from the bottom fitting of the separator that went to the intake manifold barbs made it problematic to get a consistent idle.
Without the drain the vapors and condensation would get pulled into the air box and contaminate my air filter. I ran it like this all last season. I never had any oil come out of the drain and my air filter stayed clean. The only caveat would be that I also installed a Comstock sump reed valve at the same time and that could have had a positive affect on the system.

Pete

On the Keihin FCR flatslide setup there is a random swiveling pipe, in the parts diagram its labeled "air vent"
Question. Could I hook up the oil tank vent to that via original oil seperator?
Will it cause the carbs to be contaminated with oil? or will such a small amount bleed through as to be irrelevant?
As there is no balance pipe in manifold I cant link to that as in original.
The FCR's are working beautifully and I dont want to mess them up, , but i dont have a great deal of experience or knowledge of their mysteries