Oil in the air box.

[GS750GUY]

I went out to the garage yesterday to move my 78 GS750EC out to the driveway and I put the bike on its side kickstand which I don't normally do. I usually put it back on its center stand so the bike is level during warm ups.

This time however I did not do that and I just used the side kickstand to support the bike since it would be a half hour or so before I was ready to ride.

When I went back outside after 30 minutes or so, I noticed what appeared to be oil laying on top of the crank case on the left side just under the carbs and running down the side of the engine side cover and dripping on the driveway. I first thought it was gasoline from maybe a drippy carb bowl but upon inspection it was too thick and slick and had no gas smell.

I took a clean old white T-shirt rag and wiped the under side of the float bowl and came up with nothing. But I then wiped the underside of the air box right where the side covers fit the airbox and came up with some nice yellow fresh clean oil stains on the rag.

I put the bike back on its center stand and pulled the side covers off the air box and found laying on the bottom of the airbox some shallow pools of oil. Evidently this time when I put the bike on its side kick stand and the bike leans to the left this oil will move to the left side, seep out around the bottom of the airbox side cover, and drip out onto the top of the engine crank case and run down the side of the engine cover and drip on the driveway.

There are no signs of oil drips on the floor of the garage and I usually always park the bike on its center stand which explains why I have not noticed these oil signs before and explains why none has dripped to the floor. The bottom of the air box is actually a little lower than the side covers and if place on its center stand the oil would never run out around the side covers and drip down on the engine.

The bike has just 14,000 miles on it and the air filter has 3000 on it. Could this oil be showing up in the airbox because the air filter may be dirty and need to be cleaned? I think the manual says to clean the air filter at 3000. Would this have anything to do with oil pooling inside my airbox?

As always, I appreciate your wisdom.

GS750GUY

[Nessism]

It's not due to the air filter.

Oil in the airbox could be due to blowby gasses fogging oil out of the engine through the breather, or maybe your carbs are leaking into the crankcase via the vacuum port of the petcock. Does the engine use a lot of oil? Also you might want to check the oil level to see how full it looks and go from there.

[GS750GUY]

It's not due to the air filter.

Oil in the airbox could be due to blowby gasses fogging oil out of the engine through the breather, or maybe your carbs are leaking into the crankcase via the vacuum port of the petcock. Does the engine use a lot of oil? Also you might want to check the oil level to see how full it looks and go from there.

Thanks for your response Nessism!
The day I noticed this, I checked the oil level sight glass while on the center stand and to my surprise could not even see the top line of the oil. When I started adding oil to the engine...only then did I begin to see the oil level begin to rise in the sight glass. I think I added approximately 1/2 a quart or so to bring it up to the proper level. I'm estimating I lost this 1/2 quart over the span of 1000 miles or so.
Typically, I check my oil quite frequently but the sight glass on my bike is kind of cloudy from age and is a little difficult to read.
It seems to me during last years riding season I did not have to add any oil at all.
Could I have done any damage running 1/2 a quart low?
Also, how would I check to see if the carbs are leaking into the crankcase by way of the vacuum port on the petcock?

GS750GUY

[chef1366]

The oil will smell like gas.
This is probably caused by oil blowby from the piston rings.

[GS750GUY]

The oil will smell like gas.
This is probably caused by oil blowby from the piston rings.

Could this be the case on a bike with only 14,000 miles on it?

GS750Guy

[DanTheMan]

Could this be the case on a bike with only 14,000 miles on it?

GS750Guy

Could be you've got a stuck piston ring, or your valve guide seals are hardened and allowing a lot of blowby past. How long did the bike sit without being used? The pistons sitting in one spot for a number of years can cause the rings to conform to that section of the cylinder. That or your valve guide seals would be the most likely spot for blowby to happen.
Your bike is 31 years old, and so it's had a lot of non-run time to only have 14,000 miles on it. My bike has about the same amount of blowby as yours, it consumes a quart of oil about evry 1500 miles, a little more the harder I run it, but I know my valve guide seals are toasted from a x-country trip to and from CA a couple of years ago. For now, I just add oil, probably fix it this winter when I can't ride it.
Check your air filter, clean it when it's dirty. I change oil every 1500 miles, oil and filter every 3000 miles, works well for me.

[GS750GUY]

Could be you've got a stuck piston ring, or your valve guide seals are hardened and allowing a lot of blowby past. How long did the bike sit without being used? The pistons sitting in one spot for a number of years can cause the rings to conform to that section of the cylinder. That or your valve guide seals would be the most likely spot for blowby to happen.
Your bike is 31 years old, and so it's had a lot of non-run time to only have 14,000 miles on it. My bike has about the same amount of blowby as yours, it consumes a quart of oil about evry 1500 miles, a little more the harder I run it, but I know my valve guide seals are toasted from a x-country trip to and from CA a couple of years ago. For now, I just add oil, probably fix it this winter when I can't ride it.
Check your air filter, clean it when it's dirty. I change oil every 1500 miles, oil and filter every 3000 miles, works well for me.

Thanks for your input DanTheMan!

It sat outside exposed to the elements for 4 or 5 years with half a tank of gas in it. When I got the bike it had only 11,000 miles on it and I put 3,000 on it since I restored it. I didn't do anything to the engine except replace a few valve shims, replace the points and condensors, tune it, change the oil, replace the valve cover gasket, rebuild and sync the carbs and clean the gas tank.
Like you, I change the oil every 1500 miles.
I would think that if the engine were having these kinds of problems I would have noticed this symptom right off the bat when I put my latest 3000 miles on the bike. But I didn't notice this oil situation until just recently.

So, do you mean if I just keep an eye on my oil level and keep the air filter clean I can go ahead and ride it?? Although I can do it....I'm not too crazy about doing a ring and valve guide seal job this winter.

GS750GUY

[dpep]

A half quart of oil every 1000 miles on an older bike is no big deal. Keep an eye on the level and enjoy the bike for a while.

[GS750GUY]

A half quart of oil every 1000 miles on an older bike is no big deal. Keep an eye on the level and enjoy the bike for a while.

Thanks for your help dpep! It's going to be 70 degrees and sunny here on Saturday and I plan to do just that!
GS750GUY

[DanTheMan]

Thanks for your help dpep! It's going to be 70 degrees and sunny here on Saturday and I plan to do just that!
GS750GUY

.
My Rx exactly, that's why I haven't torn mine down again (blew the head gasket not long after that CA trip). I can live with dumping a half qt in occasionally

[nhgsguy]

You can do a leak down test and see where the problem is.

[GS750GUY]

You can do a leak down test and see where the problem is.

Thanks for the advice nhgsguy. How do you do a leak down test?
GS750GUY

[GS750GUY]

It's not due to the air filter.

Oil in the airbox could be due to blowby gasses fogging oil out of the engine through the breather, or maybe your carbs are leaking into the crankcase via the vacuum port of the petcock. Does the engine use a lot of oil? Also you might want to check the oil level to see how full it looks and go from there.

Hello....I'm back again regarding my oil consumption situation.

Since I began this thread I've been watching my oil consumption closely and making sure my oil level is always topped off in the sight glass before heading out for a ride. The last few short rides (20 to 30 miles or so) I have not had to add any oil at all to the crankcase and things have seemed to be pretty normal with the exception to ocassional dribbles of fuel that I have been finding on the floor when I push the bike out of the garage. (This problem I have been addressing on another thread).

A few days ago I made sure the oil level was topped off, (level with the Full line in the sight glass), and went out for about a 25 to 30 mile ride and then parked the bike in its final resting place in the garage for the winter. I went out today to pull the battery and begin preping the bike for winter when I happened to notice the oil level in the sight glass was reading half way between the Full and Low line. I thought "My gosh!! I can't believe the oil level dropped that much in just a short 25 to 30 mile ride. I had a partial bottle of oil handy and I thought for curiosity I would fill the crankcase back up to the Full line to see how many ounces of fuel the engine used in that short ride. To my surprise it took 6 ounces of oil to fill back up to the Full line.

Then it suddenly occured to me: I remembered and highlighted in red the above statement by Nessism regarding the vacuum port on the petcock and his question about using a lot of oil.

My thought is: could what Nessism mentions above about my petcock vacuum port possibly be the cause of my high oil consumption??

Last time I went for a ride I did notice some light smoking mostly from my right exhaust pipe when I first started the bike that seemed to subside to be nearly unnoticable by the time the bike warmed up.

Again, I appreciate your mechanical wisdom!

GS750GUY

[DimitriT]

The sight glass oil level only gives a few ounces of range.

It's common for the oil level to read lower or higher after the motor
is run. Where does the oil hide? Or where does the oil appear from?

I'm guessing the top end. The cavities containing the tappets are
about the volume I would expect. So if something is keeping that
oil from draining down to the pan it will "disappear" from view. My
guess is that the oil in those cavities drain back down past the
oil pump and if the pump is stopped such that the flow is obstructed
the oil will stay up there. I've never tested this out, though.

BTW, I also get a little drop of oil under the bike after running. Has
anyone on a chain bike thought about putting that oil to use by
redirecting it to drip on the chain?

[Nessism]

To check the petcock, pull off the vacuum line and see if gas comes out, or better yet, replace the vacuum line with clear tubing and run the bike to see if it fills with gas.
You might alwo want to run the bike around with the breather line into a catch can of some sort to see if you are blowing oil out the breather. 6 oz. of oil is a crazy amount of consumption. What do the plugs look like? They would be pitch black and there would be a trail of blue smoke in order to burn that much oil.