1979 xs750 - Oil Problems

[PDXWarrior]

Hey Everyone,

I have a friend that rides a '79 xs750 special and we recently ran into a bit of a problem. When he first got the bike, it ran great, no issues and everything seemed to function well.

We've done a little chopping on the bike to bob it out, but still no problems. We haven't done any engine mods, etc. The problem started some time ago, and he relates it to the following:

He had the bike in neutral and went to let the clutch out. Somehow, the bike apparently was in gear or "went into gear" and the bike lurched forward a bit and then stalled. No biggie, completely expect it to do so. The "oil" light came on, which again, you'd expect.

He started the bike up again, and it started fine and seemed fine, but the oil light refused to go off. He later checked the oil window on the side and noticed he didn't see any oil, figuring it was low he went ahead and added some. Then added little more.

We think he added too much, because he ended up filling the window, oops. So we drained the oil and got it back to where it should be.

Now for the problem. When riding (usually at higher rpms, but sometimes in lower rpms) the bike will push oil out the crank case breather. This results in a huge mess as it runs over the top of the crank case and then off the left side of the engine, onto the foot peg and exhaust.

It does stop after a while, but then when you check the oil window later, it's too low again (not showing). Seems like it's building some sort of back pressure.

We've read where this could be related to rings, but if that were the case, we should be burning oil and the bike burns clean. The only time it 'smokes' is when using the choke, but again - you'd expect that.

Our current thought is that the oil pump is either not working or is plugged. We are planning on tearing this down sometime in the next week or so, but would really like to hear any other suggestions you may have.

All thoughts are welcome and encouraged! My apologies for such a lengthy first post, but too much information is better than not enough

Thanks -

pdxwarrior

[rpgoerlich]

Still sounds like it has too much oil in the crankcase.
Put it on the side stand and see if the oil level drops below the window. New oil is pretty clear and if it's above the window it's hard to see it.

The oil light doubles as a brake/tail light indicator when it burns out. You might have a bad connection to the tail light or maybe a bad fuse block connection.

http://www.yamaha-triples.org is a good resource for the Triples.

[PDXWarrior]

Please allow me to ask a stupid question... should the oil be measured when the bike is standing level or when it's on the side stand?

Additionally, it doesn't "lean" as much as it used to, we dropped the back down a good two inches or so, causing the bike to be pretty up and down even when on the side stand compared to it's original position.

It does seem to stop once the oil is "down" and we've considered maybe it was "too much" but we are concerned since we're planning a big ride in a few months. Want to make sure this is 'trip ready'!

By the way, interesting comment about it doubling as a brake/tail light indicator. We did switch out the rear lights, wonder if that could have something to do with it. But strangely, the light wasn't on even after switching the lights. Not that I recall - will have to double check that with him.

[soccer4m]

oil

Hi,,,put the bike on the centerstand for oil checking, or keep it level when off the stand otherwise it will be way off. Also, I have the same exact bike and the xs750 site has tons of info on it. THe second gear usually goes bad, but its an easy one hour fix if it happens to you.....I love the bike, lots of torque, great at high speed and a cool sound.........Use 10/40 every 2500 miles and the bike will last forever,,,also put a fuel filter inline to the carbs to keep out any crud as ever a little will screw up the carbs. Regards, Mike in S.DIego

[PDXWarrior]

Checking the wiring should be a good simple place to start, along with oil levels.

Since this bike doesn't have a dipstick and instead just the viewing window, is there any other way to check the level of the oil? Preferably without measuring "what you put in"

Also, is there a way to confirm that the oil pump is working or that oil is actually cycling through the motor, ie. not plugged up?

-pdxwarrior

[cywelchjr]

Just make sure the bike it level side to side when checking. The oil should be between the two lines beside the little window when the bike is sitting as if it was on the center stand. If you put it where it says, even with it leaning a little bit, it will be way over filled, and will do exactly as you describe.

The is true even on the new yamaha's, including the ones that don't even have a center stand.

[fredintoon]

- - - Since this bike doesn't have a dipstick and instead just the viewing window, is there any other way to check the level of the oil? Preferably without measuring "what you put in"
Also, is there a way to confirm that the oil pump is working or that oil is actually cycling through the motor, ie. not plugged up? - - -

Hi Scott,
because my bike has a sidecar it's automatically held upright so the oil porthole always reads right. The downside is that I can't see the oil porthole without using a mirror on a stick.
You can't fix a dipstick onto the oil filler cap neither because it would rub against the clutch.
What I did was to straighten out a ~4" hose clamp and cut the worm drive off then bend the strip into a T-shape.
This makes a handy dipstick that'll fit in your pocket to use when the engine ain't running.
And you'll know the oil pump ain't working PDQ because the engine will seize up when it quits.