Topic: Gas in oil- Troubleshooting

[Mr.Moose]

Hope someone has some input for me on a problem I've got on my recently purchased 1976 CB400F. I am a complete beginner on motorcycles, and have been reading in this forum, but have some questions.

Checking my oil, I realize the level is too high and the oil smells like gasoline. Red line in picture shows the level on the dipstick. From what I've been able to understand from this forum 3 thing have to fail at the same time for this to happen:

1. Petcock failing or left in "ON" position.
2. Floaters failing, or stuck.
3. Overflow tube is clogged. Cause this carb has an overflow tube doesn't it?

So, my questions:

Where do I start to find the source of the gas leakage? The bike was transported in a trailer for a 600km drive, can that cause gas to spill and find its way into the cylinders?

After getting the bike, I've run the engine, mostly idling, for about 10 minutes in total before checking the oil level. Can this have caused serious damage to the engine, and what would be the tell tale signs? I am a little worried not having any idea how serious this is.

I've included a picture of the oil. Does the color look right? Supposed to be changed this spring and run only 30 km (about 20 miles I think) since then. The oil does not light up when putting a match to it, so can it be something other than gasoline that makes the increase in volume? There is also a slight burnt smell from the oil, but very faint.

Can I now, change the oil, fill up the gas tank, let it sit and see if gasoline gets back in the oil? If I do this, do I then also need to change filter? Filter is also new.

Any input is very much appreciated! Thank you!

[SOHC Digger]

Change the oil and filter. Fuel will reduce the viscosity of the oil and will remain in your oil filter even if you change the oil. Change both.

Next, remove the fuel line from your petcock. Observe if it leaks when off.

Pull the bowls off your carbs and make sure the overflow tubes are clear.

Next, put everything back together and check for fuel coming out the overflows.

The high oil level might be the result of whoever did the last oil change putting too much oil in. Check your owner's manual and only put in the specified amount. The gasoline or burnt smell could be from compression leaking past your rings.

[seanbarney41]

SOHC diggers got you covered...I highly doubt you did any damage...

[Mr.Moose]

Thank you very much for the quick reply, SOHO Digger. Will follow your procedure!

To get the bowls off the carbs, do I need to remove the carbs, or is there some specialist tool so that I can reach? Seems like a tight spot.

When it's all put back together, do I the just leave the petcock on, and that should make fuel overflow? Wouldn't the floaters stop any overflow if they were working properly?

And, again: What would be the signs of damage to the engine caused by this? Affraid I've ruined something before even having the chance to ride it!

[Mr.Moose]

That's a relief to hear, seanbarney41! Thank you

[SOHC Digger]

Your best bet for getting these bowls off is a 1/4" drive ratchet with a 1/4" socket and a Philips bit, the kind you would put in a drill... Should give you both the clearance and leverage you need.

About the only sign of possible damage you will see is metallic flaking in your oil from bearing material being wiped out. But I agree with seanbarney41... I highly doubt you did any damage in that short amount of time.

Turning the petcock on and looking for fuel out the overflows is your way of seeing if the float needles are doing their job. If you get fuel out the overflows when everything is back together, I would replace all your float needles.

[Mr.Moose]

Super. Then I've got something to work with! So basically, for gas to get into the oil, the float needles need to be failing, if I understand you correctly, SOHO Digger. Cause it shouldnt flow past the carb into the engine even if the petcock is on, and the overflows are there just in case the needles fail? Hope this is a job that can be done by a beginner. I do have service and repair books for the bike, and will be going too shopping tomorrow.

Thank you very much! Will report back.

[SOHC Digger]

You got it. The petcock is there so you don't end up with a tank full of fuel on your garage floor if one of your float needles fail.

I do carb rebuilds too, so if you get to feeling you're in over your head, give me a shout and I'll walk you through it.

[Mr.Moose]

Thank you so much, SOHC Digger, really appreciate it. What did people do before the internet?!

Think I'll have the time to try and fix this tomorrow.

[SOHC Digger]

Thank you so much, SOHC Digger, really appreciate it. What did people do before the internet?!

Hell if I know. This is the best time to be a bike enthusiast...

[Mr.Moose]

Okay! Took me 2 days and 5 different stores to find a tool that would fit to get those bowls off, but finally got it. Got some more questions and some pictures:

First, drained oil, turned out it was only 3,7 liters (supposed to be 3,5) so why I read so high oil level (did it 3 times, only dipped the stick) I do not know. But, does the color and particles in the oil look normal for oil that has been sitting in the bike since this spring and run about 30km (20 ish miles)? There was some fuel smell, and it drained a much lighter liquid towards the end.

Petcock is working, bowls came off, overflow lines are open. Only thing I could see was some particles in the bottom of two bowls, and a gasket seemed to be loose in one (see red arrow). Could this be a problem?

First 5 times I started the bike it started right up and ran nicely. Now, as it did before the oil change as well, it does not want to idle properly and I have to fiddle alot with the choke and accelerator for it to not stop. Maybe this has nothing to do with gasoline in the oil at all?

I'm very happy for any kind of input or tips you guys wanna give!

[flybox1]

You will find working on the carbs is much easier if done OFF the bike.
Getting the airbox haves separated, bottom off first, then top off, makes getting the carbs in and out much easier.
Might take you all of 5 minutes, including the throttle cables.

That squashed oring is not good.
Id pull that jet and install a new OEM oring around it. 
It can allow gas to bypass the jet inlet, making rich running for that cyl.

Fill it back up with 3.5L of new and go ride.
Change it again after another 200K, to help flush it of any leftover particulate, and then resume regular maintenance, and more frequent riding 

[SOHC Digger]

Those carbs look VERY clean. My guess is that the PO probably never used the petcock and just left the fuel on. Then he had the overflow issue, which caused fuel to get in the oil, and he pulled the carbs and had then cleaned and rebuilt. Whoever installed the mains pinched that o-ring. The overflow problem was probably remedied with the carb rebuild.

I agree with flybox1. Fill the oil up properly, fix that o-ring, and ride the bike. Check your oil level often, and change the oil after another hundred miles or so.

[Mr.Moose]

You will find working on the carbs is much easier if done OFF the bike.

I guess it is... but I'm really a beginner at this, so removing the carbs feels a bit like attempting brain surgery or something where the consequences for permanent damage is high!

That squashed oring is not good.
Id pull that jet and install a new OEM oring around it. 

And  this is something you think I can try to fix myself? I don't risk to ruin something finely tuned in the carb when putting it back together? I've been told that any carburetor job on this bike is difficult stuff. And does it have to be OEM? Not sure I can find that here in Norway and have to order from abroad.

Those carbs look VERY clean. My guess is that the PO probably never used the petcock and just left the fuel on. Then he had the overflow issue, which caused fuel to get in the oil, and he pulled the carbs and had then cleaned and rebuilt. Whoever installed the mains pinched that o-ring. The overflow problem was probably remedied with the carb rebuild.

I agree with flybox1. Fill the oil up properly, fix that o-ring, and ride the bike. Check your oil level often, and change the oil after another hundred miles or so.

PO said bike was fixed some 10 years ago, stored dry and warm, and not ridden much since. But oil has been changed every season, but it doesn't exactly look fresh that oil, does it?

Again, thank you guys, very helpful this.

[Mr.Moose]

Okay. So, I've gotten my motorcycle licence and started riding my bike. I've ridden it maybe 50km (I think that is about 35 miles) since last oil change. The oil level is again high on the dip stick, smells like fuel, and has what looks like black soot in it. The spark plugs are black, but that might be because I'm not familiar with the choke yet, and have't ridden it enough. Symptoms when riding: loss of power when going on the throttle, and a little black (not a puff, but you can see some colour on the exhaust) smoke when revving the engine.  The overflow lines from the carburetor are open, and I've made sure the petcock is off when the engine is not running. Does anybody have any idea what might be going on? Can worn piston rings cause this?

[Trad]

If the plugs are black with dry soot and not oily you have a bit of a rich condition. Did you ever fix that pinched o-ring on the main jet?

If you're just putting around at idle speeds around town you aren't getting the plugs up to a self cleaning temperature. This is normal for these bikes. Try and go for a more spirited ride on the freeway for 20 minutes and see how the plugs look.

You also have air/fuel screws you can use to dial in your mixture.

You can also do a quick float level check via the "clear tube method" do a quick search for the basic how to. It's easy and pie and you can verify if you level is too high, possibly adding to the rich condition.

Have you been getting gas coming out of the overflow tubes?

Now to address your oil level issue. Make sure you are checking the level while the bike is warmed up on a level surface and only putting the dipstick in without threading it down.

Also, there can be residual oil in the system. You may not be draining it all out. I'm willing to bet you are not getting it all drained then refilling the specified amount, not accounting for the residual. Drain the oil when warm, kick the bike over a few times and get all the oil out of the filter housing.

Worn piston rings would be blue/grey smoke and your plugs would be oily, not sooty.

You have a minor problem here, don't stress out too much about catastrophic failure. haha.

[Mr.Moose]

You have a minor problem here, don't stress out too much about catastrophic failure. haha.

Haha! Trying not to! Smelling the dip stick and having nightmares about blowing up!

No, but, thank you for calming me down

Haven't prorperly ran it warm at all, 30 min city driving is the most I've done (partly because of having brake problems, another thread about that), so no idea how the bike behaves after running an hour.

Plugs are black with soot, yes, can't feel oil on them.

No gas from overflow tubes at all, I've been checking for that regularly.

Oil level is measured warm, on center stand, and not threading the dip stick down, still high. Pretty sure I drained it properly the last time, but I'll do it again to be sure.

"clear tube method" is a good idea, on the to do list now! And running rich, that can cause some fuel to get in to the crackcase and contaminate the oil so it smells like fuel?

I did change the o ring, but I didn't have the patience to order one (would take a couple of weeks) and I found one in a local shop. I pulled it out again now, and... it isn't a perfect fit. I measured the old one to be 1mm thick and 6 mm outer diameter, but googeling it now I found this http://www.sohc4.net/carb-o-ring/ that says: "Main Jet: 1.2mm cross-section x 3.5 mm ID". So I guess I got the size wrong. Is 3.5mm here the inner diameter?

[flybox1]

use only OEM o-rings or the properly sized VITON o-rings.
anything else will not withstand living in gas, or exposed to carb cleaner.
highly unlikely gas is in your oil when its not also pouring out your overflow tubes

[Mr.Moose]

yep, they were the viton kind, just bad fit, see if I can find a better one.

[Mr.Moose]

No luck finding a better fitting o-ring, so now I've ordered OEM jets, with the ring on them. Autumn has arrived here, so hope the new jets arrive before the snow does!  When pulling out the jet, there was no o-ring separating the jet and the needle set. The ring marked yellow on this picture, is that the one on the jet, or am I missing a ring? If I am missing it, does anybody know the correct size of this ring?

[flybox1]

No oring between the jet and emulsion tube.   
Just the one on the waist of the main jet.

[Mr.Moose]

Finally got new jets, and fitted them. Weather forecast says 5 days of sunshine untill autumn is here to stay, so hope I now can get som riding done!

But, more questions I hope you guys can help with:

My plugs are still black and sooty. Got some black smoke when accelerating. Indication of rich mixture, right?

But, I've also got loss of power when accelerating from idle, it dies momentarily, almost stalls, which is indication of a lean mixture. I've read that this can be due to too lean when idle, and too big jets making it too rich when under power... how do I best go about to check if this is the case?

And my oil has still got a pretty strong fuel smell to it. Checked the float hights, and to my understanding one might be a little low, while the others are ok. Is the clear tube method reliable?

[Redline it]

if you are just mentally gifted in common sense for where to start on bowl removal. Start on the outside remove #1 carb bowl,  remove the float and pilot jet and overflow tube, being careful not to accidentally hit the float pin towers, they're thin. then move to #4 the right side and repeat, move to #3, then #2. Assemble in reverse, #2 needs all the room it can get, don't tighten the screws but just hard pinch finger tight do it in cross steps, x pattern (unless you know it's not binding on anything.) If you have leaks then tighten screws just alittle more. after riding, check for any backing out.

[alacrity]

Thank you so much, SOHC Digger, really appreciate it. What did people do before the internet?!

Hell if I know. This is the best time to be a bike enthusiast...

Damn straight.