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GS450L blowing oil/gas out of the crankcase vent - HELP

  • Thread starter Thread starter charford
  • Start date Start date
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charford

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Hi, I could really use some help on this one. I recently bought a 1981 Suzuki GS450 off a guy (it had probably sat for a year or so). The bike wasn't running but I was able to get it running after a couple hours in the shop. The bike literally looks and sounds like it is running perfectly, which really surprised me. I took in around the block and was astonished by how great everything sounded and felt. There bike fires up and runs instantly, sounds great at idle and has no engine miss or anything like that.

I was planning on thoroughly disassembling and cleaning the carb, but I was beginning to think I hit the jackpot and wouldn't even have to do that. Anyway, after running for a little bit an oil/gas mixture begins to rocket out of what I believe is the crankcase vent. The vent is an opening facing the rear of the bike that is on the very top of the engine. I believe it sits right above the cams and my understanding is that this is the crankcase vent which is meant to vent the air, but not spew some sort of oil/gas mixture all over. I also have heard that their is supposed to be a hose going from there to the air box; although it is for emissions and is not necessary (there is no hose on mine currently).

I wanted to find out what and how much was coming out of there so I attached a hose to the vent and ran it into a large water bottle to collect the fluids. I drove the bike approx 2 miles and I had filled up a half liter water bottle. This is clearly too much so I parked it and I am trying to figure out what to do next. I think there is gasoline in the mixture and I am wondering how the gasoline is getting into the engine when the engine is running so great. If there was a stuck float and gas was dumping into the engine, wouldn't the engine be running like crap? My first step is to take off the vent and see if everything is in order up there. I assume there is some type of air/water separator and I need to make sure that is still intact. Also I need to drain the crankcase to see how much gas is in there, and change the oil.

Basically I wanted to find out if anyone knows what is going on here. Is there supposed to be a hose off of that vent? Is it supposed to go to the airbox? Is there some sort of a return that just puts that oil back into the crankcase (if that is the case, maybe that much fluid coming out of the vent is normal)? What should I do next?

I had a friend that told me the floats are stuck on the carb, but I just don't see how any of the problems I am having add up to the carb at all. Unless I drain the crankcase and find alot of gas.

Thanks,

Chris
 
Check the oil level; if it's high, you may well have gas in the oil. Proper way to check the oil is to put the bike on the center stand and either check the sight glass or if your bike is equiped with a dipstick, measure the level without screwing the dipstick into the crankcase cover. There are two ways gas can enter the crankcase; flowing backwards down the vacuum line if the petcock has failed, or by overflowing floatbowls. The later issue will be worse if your petcock is remainging in the Prime position.

Good luck.
 
I have known bikes to bore wash & fill the crankcases with fuel its usually down to a combination of the fuel (vacum) tap not shutting off properly & stuck carb floats

Have you checked the oil level ?
Does the oil smell of fuel ?

Modern unleaded fuels go off in a matter of weeks & will "varnish" in the carbs gumming everything up !

Having said all that i've never known a bike to kick that amount of fuel out of the breather unless there is another problem, valves? rings?

Does it smoke at all while running ?
 
The oil level is normal, but I need to drain the crankcase to see what the oil looks like. On the dipstick the oil looks good but it smells like there is gas in there to me.

I haven't noticed any smoke when running. I won't be able to work on it again till tomorrow- so I will drain it and see what happens. I will give you an update as soon as I can with pictures. Thanks for the help thus far. Should I have the fuel turned on? or should I have it set to prime?

Chris
 
Fuel tap should be left in the on position :-D

The smell from the crankcase could either be fuel as discussed above or it could be from combustion which indicates a head gasket leak
 
I would change the oil and filter first and see what happens. You could also have a stuck valve and/or stuck rings from sitting so long. After the oil change run it awhile and see if it works it's way out.

A little trick you can try while the oil is drained out is spray PB Blaster or Marvel Mystery oil in the cylinders and let it sit for a few days. Keep applying the oil periodically.

I would also pull the carbs and clean them. Check valve clearance then check compression.
 
Alright guys I have an update for you.

Last night I changed the oil in the bike, as you all predicted there was a ton of fuel in the crankcase. I drained all that junk, and refilled the engine with 3 Quarts of 15W40 oil. I drove the bike about 5 miles to see if it would refill my water bottle setup. After about 5 miles I had not a drop come out of the crankcase vent. I brought the bike back to the shop and had about a teaspoon of fluid in the bottle, which I am sure was just condensation from shooting hot air into a bottle on a cold night.

I plan on draining the oil again tonight, and if I don't see any fuel in the crankcase my guess would be that I am in the clear. Does everyone concur? If there is no fuel, no overflow, no blowby, and the bike is running great- I would assume that I can skip the carb cleaning- Correct?

I also plan on doing a compression test tonight, just to make sure everything is square with the rings. I haven't gotten my clymer manual in the mail yet so does anyone know what compression I should be looking for?

Thanks,

Chris
 
Also, does that bike have an oil and fuel filter? If so does anyone know where they are?
 
Only fuel filter, unless the previous owner installed an aftermarket one, is the screen on the petcock (inside the tank). Oil filter is on the front of the engine, down between the pipes on the bottom.

If you have fuel in the oil it will likely happen again unless you eliminate the cause. Either the petcock is failing and letting gas run backwards down the vacuum line, or the float needles are allowing gas to over flow the float bowl - sometimes when the petcock has failed it allows gas to flow all the time thereby putting too much load on the needles. Number one reason for overflowing is debris in the carbs, maybe coming from the tank so check that for rust while you are at it.
 
Nessism said:
Only fuel filter, unless the previous owner installed an aftermarket one, is the screen on the petcock (inside the tank). Oil filter is on the front of the engine, down between the pipes on the bottom.

If you have fuel in the oil it will likely happen again unless you eliminate the cause. Either the petcock is failing and letting gas run backwards down the vacuum line, or the float needles are allowing gas to over flow the float bowl - sometimes when the petcock has failed it allows gas to flow all the time thereby putting too much load on the needles. Number one reason for overflowing is debris in the carbs, maybe coming from the tank so check that for rust while you are at it.
Click to expand...

I agree 100% :-D
 
I will try and check all that and get back to you guys, also I will have some pics tomorrow.

Thanks,

Chris
 
Quick update for you, and some pics. I just took the bike around the block- at about half throttle it begins to sputter and loses power. If you keep going to full throttle you can come out of it. Oil level looks ok, but it smelled of gas again (maybe that is because it had gas in it yesterday). I am going over right now to drain and inspect the oil. I have decided I am definitely going to take the carb off and clean everything, hopefully put new orings etc but I am currently not having any luck finding a rebuilt kit. I am not quite sure how to go about addressing the petcock problem. Is there any way to diagnose this, or should I just replace the petcock completely. A new one costs about $50 so I would rather only replace it if I have to. I have attached some pics, not bad for a $250 bike huh!

View attachment 3045
 
Turn the petcock lever to ON and pull off the fuel and vacuum line from the petcock. Attach a section of hose to each (put the fuel line section in a gas can). There should not be any gas flowing with the lever in the ON and Res positions, but gas should freely flow with the lever on Prime. Pull a vacuum on the vacuum line and check to see if gas flows when the petcock is in the ON and Res positions. The vacuum diaphragm in the petcock should not leak – if it does, make sure gas is not going to flow backwards into the engine.
 
Alright guys I have a big update for you.

I drained the oil again and it looks like it has gas in it again. I then removed the seat and fuel tank. I did a compression test and both cylinders had 135 psi which I assume is close to good. When I cranked the bike over for the test I noticed a slow drip of fuel started running out of the crankcase drainplug. At this point I had the tank off so this might have been just stuff that didn't drain before or from the filter.

I then unhooked the throttle, air box, and intake boots- and then slid the carb out. I took off the float bowls and they looked pretty clean to me. The gaskets looked intact as well as the floats. I haven't spend a ton of time with the carb yet but I flipped it over and moved the carbs and the needle valve (or whatever they are that the float pushes) seemed to have full range of motion. Then I took off the top of the carb and what I assume is the diaphram looked intact. I haven't gone any further yet because frankly I don't know what I am doing and my dad is going to come over and help me. I assume I should disassemble the whole carb and check/replace all the Orings.

I have not tested the petcock like you suggested yet but I set the tank up with a bucked underneath it and when I set the petcock to ON there is no drip coming out of it. When I set to prime of course there is a full stream. I need to get a piece of hose for the vacuum end so I can suck on it and see if it starts flowing. Also I checked over the intake boot. One of them looks like it could stand to be replaced, and both of the orings on the engine side are flush with the boot (aren't they supposed to be bulged out like an oring). Both of these oring look structurally intact (unlike the picture of a broken intake boot oring on cycleorings.com

What is your diagnosis's and what should I do next? I can take pictures of any of this if you want me to, just tell me what to take pictures of.

Thanks you guys don't know how much I appreciate this,

Chris
 
QUIT DINKING AROUND AND REPLACE THAT EFFING PETCOCK ALREADY!

Hope that was clear but not too rude... :-D

How much have you already spent on fresh oil to avoid replacing a $50 part that needs replacing on every GS? Buy a new one from Suzuki and forget about this problem for another 20 years.

PLEASE stop riding the bike until you do replace the petcock. You WILL damage the engine. And in case you were wondering, petcock rebuild kits usually don't work. Petcocks from eBay are also often disappointing.

Once you replace the petcock, you may need to clean out the float valves once again if the carbs overflow -- sometimes an old deteriorated petcock will dump little flakes and chunks of rubber into the carbs and make the float needles stick.

Also, the intake o-rings should definitely be replaced. They're not supposed to be flat and hardened.
 
Yeh, maybe a little rude, but to the point nonetheless. :-D

Where do you live, CharFord? Is there a Harbor Freight Tools store near you? They have a hand operated vacuum pump that will save you from swallowing whatever you would apply vacuum to orally. :arrow: You can get the MityVac system, or the US General simile, there. Great investment to save you a mouthful of fuel, or bleeding your brakes, the list goes on...

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=39522

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=92474
 
If the petcock is not leaking with the tank off it might be serviceable. You need to suck on the vacuum line to see if there is a leak - once you pull a vacuum it should hold - no bleed down. Of course be careful or you might get a mouthful of gas which won't be fun.
 
Calm down there bwringer, if I have learned anything from working on cars it is that you don't start replacing things until you have diagnosed the problem and ruled out all the options.

I just tested the petcock. In the prime position gas flows freely. In the on and res positions I sucked on the vacuum hose and gas flowed freely out of the gas line but not a single drop came down the vacuum hose. I sucked as hard as I could (until there was a full stream) and still nothing. Does this indicate that there is nothing wrong with the petcock or should I replace it anyways?

Chris
 
charford said:
I just tested the petcock. In the prime position gas flows freely. In the on and res positions I sucked on the vacuum hose and gas flowed freely out of the gas line but not a single drop came down the vacuum hose. I sucked as hard as I could (until there was a full stream) and still nothing. Does this indicate that there is nothing wrong with the petcock or should I replace it anyways?

Chris
Click to expand...


If there was any vacuum "bleed down" while sucking on the line I'd replace the petcock, otherwise, you can leave well enough alone.

In support of Brian’s urging, the fuel system is full of rubber parts that deteriorate with time. It’s one of those pay me now or pay me later sort of things. From my experience, for example, I wouldn’t bother even trying to get one of these old GS bikes back on the road (assuming it sat for a while) without doing a complete carb teardown and rebuild with new O-rings. There are endless posts in the Technical forum from people struggling in one way or another to get their bike to run right because of carb problems. Establishing a baseline where by you know for a certainty that the carbs are clean, and the intake boots are sealing, is a clear path forward.
 
Last edited:
Agreed. I just purchased all the carb orings, new intake boots w/ orings, and I went ahead and bought a new petcock because in the end you are right- it is only $50 so you might as well not even think about it. The carb actually looks pretty good and I am really starting to wonder if the intake boots are the problem here.

I should get all this stuff and have it done by thanksgiving- I guess if it is still having problems after that then I need to start thinking about head gaskets. Will update when I finish all this stuff.

Thanks
 
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