Topic: oil line question for custom oil tank... another oil breather hose spewing oil..

[samm_j2]

So....

I have a custom oil tank on my bike, 78 cb750f. It definitely is smaller than the stock oil tank. It is triangular in shape  and fills the lower half of the tringle in the frame. It has two connections at the top for hoses (breather and return) and two at the bottom (oil feed and drain). It has a hose running from the bottom of the tank to the oil feed, it has another hose running from the return to the top of the tank. The other connection at the top I am using as a breather. I have been just running the breather of the oil tank to atmosphere. The only problem is that if I fill the oil tank then it spits A LOT of oil out of this breather. It does this not when just sitting but when I take it around the block. It will spit it out and leave the tank about half way empty. This is how I have been running it as I was thinking maybe I just kept over filling it and the geometry of the tank wont allow it to be full or somethin.... It spits out so much oil that if the bike is on its side stand the oil piles to the left and leaves the feed above the oil remaining in the tank. So the bike can not idle on the kickstand else it starves. The lack of oil in the system has always concerned me so I have changed the oil A ALOT! I also do not ride the bike much, it has less than 500 miles. I am starting to think this is not normal though. Do I need to connect the breather from the oil tank to the nipple on the back of the transmission case? If I do this do I still need to have some sort of breather for the tank?? As of now I have a hose going from the transmission case to atmosphere, a hose from the cam cover to atmosphere. I have the breather hose from the oil tank running up high before going down to the ground/atmosphere.

info on the bike is I have rebuilt the entire motor, 836 Wiseco pistons and a cam and other goodies but not sure any of that is relevant to the oil breather DUMPING oil. The bike has about 130 psi on all 4 cylinders on my compression tester (not sure if it should be more? tester is OTC with some long ass tubes. I figure since they are all the same number it is a good sign). I have also done a leak down test and it is at 99%.

the bike runs very well and pulls very strong.

I have searched this forum and others trying to find a solution and cant seem to get a simple solution. Figured it was time to make a post.

any help would be appreciated. thanks.

[dusterdude]

I haven't looked at my 750 but my panhead has the vent on the engine and that hose runs to the top of the tank along with the return line.

Sent from my LM-X420 using Tapatalk

[69cb750]

The breather is 3" above the oil on an original tank.
You need at least 1" and 2" would be better.
Connect the tank breather to back of engine and oil will spit into engine rather then ground.

[754]

Yeah you are probably too small a tank, you can run vent up to a catch can  aka puke tank...
 It may not even come out if hose is like 8 or 10 inches long., and going up... right now its easy to come out, too easy.
 Put a restrictor in end of line 1/8 hole  be maybe ok.
 If it did hook up to tranny , pump will bring it back, but i think its just too easy for it to go out right now.

[Medyo Bastos]

Run the engine at idle; look in the filler hole; top off tank to 1/2 full at idle; anymore and you will wear it up your back. I’ve been riding cb750 choppers since I was 12. Custom oil tanks get filled differently. You can run an oil cooler and remote tank if you want more oil in your system, just be sure you fill it the same as above. You won’t pop your push in cap, and you won’t run oil up your back.


Sent from my iPhone using Tapatalk

[samm_j2]

Thanks for the replies everyone.

I am going to route the breather to the back of the transmission case and hope that things don't explode. I will probably also move the feed to the kick stand side of the bike so that it is as submerged as it can be when on the side stand.

If anyone has any other inputs I would greatly appreciate it!

thanks