DOHC 1980 cb750

[Wickedfast17]

As stated in the title i have a 1980 cb750 with dual cams, i recently purchased the bike with unknown miles and have very little knowledge of these bikes. It has pod filters and was tuned for them, the left side breather hose had a plug in it which is something i will fix but i am having a few other issues id like to figure out. First is the oil absolutely blowing out of the right side breather at high rpms and high speeds, maybe there is a possibility the engines werent made to go this fast but the oil loss there is a huge issue. I do also have a bit of oil coming out of seals hand maybe a tiny drip in the base gasket i will need to fix but i wouldnt think any of that would be related to the oil blowing oht of the breather. Another issue im having is with the transmission, i had it jump out of 3rd at about 6k rpms yesterday multiple times and every gear shifting up i can feel odd vibrations almost like if the syncros were out in a manual car. also if anyone knows of a good aftermarket clutch that would be a huge help as most of the places i would normally order from dont carry anything for street bikes. Thanks

 

[brettp]

Have you checked your oil level per the manual? It might be over filled, hence the pressure pushing it out the breather. I don't know if this could be the case, and would like to hear from others, if it is possible your oil pump not working could have the same symptom.
Whatever the problem is with the transmission, start with the clutch. Open it up and take a look. Go from there.
I don't know anything about aftermarket clutches for these bikes, sorry I can't offer advice on that one.

 

[Wickedfast17]

Have you checked your oil level per the manual? It might be over filled, hence the pressure pushing it out the breather. I don't know if this could be the case, and would like to hear from others, if it is possible your oil pump not working could have the same symptom.
Whatever the problem is with the transmission, start with the clutch. Open it up and take a look. Go from there.
I don't know anything about aftermarket clutches for these bikes, sorry I can't offer advice on that one.

I am unsure of the directions in the owners manual for checking oil, i read in a forum somewhere while trying to find the cause a week or two ago to warm it up and take it for a ride first, something about the oil sitting somewhere else in the engine, i then clean the dipstick and lightly set it in the hole and remove it without threading it in as you would for any bike. It was just a tad over full when i got it and I thought enough had come out now as when i had last checked it was in the middle of the ribbed area on the dip stick however after a 40 mile ride at an average of 120mph my toes were drenched and checked the level and was somehow at the top of the ribs on the dipstick. I will have to look into how to properly check the oil i guess. Never put too much thought into the process, just do it like my race bikes.

 

[Wickedfast17]

Also i know some bikes came with oil tanks, was that just the pre79 sohc engines or would my 1980 dohc cb750c have come factory with one?

 

[brettp]

I don't think there is a tank on the DOHC bikes. I've never seen one on mine, anyway. If you are still full you need to empty some. Shooting oil all over your shoes is one thing. Shooting it all over the road is bad for anybody behind you.

 

[Nylundarn]

There is no oil thank on the DOHC, you are meassuring the oil the right way. When I did a oil change following the service manual the level came out a little bit low, so I just kept riding and adding until it covered the whole ribbed area.

Regarding the breather hoses, I read that they should never be plugged completely. Instead install small breather hose filters.