Oil Burning and Inconsistent Idle

Hello!

I bought an 83 XJ750 Midnight Maxim last year right before winter. I owned one back in the late 80s and always loved it, so when I found this nearly pristine bike on sale a couple of blocks from my home, I decided to pick it up.

Unfortunately, I'm experiencing a couple of problems that are making wonder if I should sell it. I've already put another $500 into this bike, but I can't seem to get the idle to sit at a consistent level, and now I've found this spot where it's burning oil.

First is the inconsistent idle. I had the carbs rebuilt and sync'd and I still have this problem. When it's cold it'll idle at about 1200rpm (where the shop set it after the rebuild), but when it gets warm, it'll jump up to as much as 3500 and fluctuate between 1200-3500rpm -- spending most of the time between 2500-3500rpm. Once it a while it'll fall all the way back to 1200 and just sit there, but most of the time time it likes 3000-3500

Just to see what it would do, I left it running in the driveway for about 40 minutes:

0-10 min: 1200rpm (consistently)
20-35 min: 2500rpm (consistently)
35-40 min: 3500rpm (consistently)

No fluctuations like when I drive it around town. So if I leave it alone it seems to be more consistent than if I'm riding it.

I was hoping the rebuilt carbs would have fixed all this, but it acts exactly the same as before the rebuild.

OIL:

After 40 minutes I noticed oil smoke. I knew something was wrong before that since I could tell I was breathing in something noxious after the 45 minute rides to the shop and back, but I couldn't see where it was coming from. Well, it's coming from here:



I tried to look this up in my Haynes and Yamaha manuals, but I don't know what this is. I'm assuming it just needs a new seal, but I don't know what seal to order since I don't know what this is. Can anyone help me?

Thanks everyone! I appreciate any help you can offer. I love this bike and really want to keep it, so I'm hoping I can get these two issues resolved.

 

Personally I wouldn't have left an air cooled machine running on the spot that long without a good fan, perhaps the oil got too warm & thin and that made it leak? To be honest the oil looks like it could be coming from inside the ignition cover (the round one above oil held on by 4 screws) :?

Welcome by the way, please check the brake links in my signature before you ride again, we like you alive

 

Thanks for the response. I wouldn't doubt that the leak was made worse by the long idle, but my throat was raw from breathing in something on the way to and from the shop, so I'm sure the problem existed in some form before I did that.

I just ran my finger around the ignition cover and there's no real sign of any oil, so I don't think it's coming from there.

But then I did something even dumber than leaving it idle for 40 minutes: I broke that little bolt:



Metal fatigue. I don't know if you can see it, but there's a bit of oil welling up inside there.

Thanks for the heads up on the breaks

 

Ahh, not good. But chances are that's where the leak was coming from anyway as it was already cracked so you would've had to try and remove the bolt either way.

You should be able to get the rest of it out still if you're careful not to let the allen key slip, and I'm pretty sure member & supporting vendor "Chacal" (XJ4Ever) will have the bolt & o-ring you need...

 

Awesome. Thanks!

 

I would take the ignition cover off and just check inside towards the bottom.

Thats a common place for oil to leak out of when gas mixes with the oil and makes it thin, which i think the idling while stationary could have possibly warmed up the oil and thinned it out enough to do just the same.

 

Worth checking just in case, but in this instance I think the leak was probably caused by the damaged bolt (if you look at the lower part of the broken off head, it looks to have oil drawn up into a crack by capillary action.

I wouldn't start the engine until the bolt is fixed since the whole of the engine's pressurised oil supply depends on a good seal there by the way, and leave it in place till you're ready to replace it since it's likely oil will want to leave via the hole, quickly...

EDIT-: Chacal's profile, can PM or email him from there http://www.xjbikes.com/Your_Account/profile=chacal.html

 

Yes, we do have that oil galley plug and the o-ring that goes on it.

However, wazimoto's advice is also good, pull of the the oil pump cover and see if there is oil in the cavity (there should not be any, at all). If there is, you have additional issues to deal with............

 

Ignition cover Len

It's 4.30 AM here, you should be fully awake by now over there lol

EDIT-: it is Sunday though so I'll let you off haha :lol:

 

Thanks everyone. I'll take a look inside the ignition cover just to be safe.

Chacal: I've sent you a PM about ordering these parts

Anyone have any thoughts on the inconsistent idle issue? I saw a different post on the subject that discussed a vacuum issue that was thought to maybe cause such behavior, but the thread seemed to quickly head into carb sync'ing once it was realized that the YICS tool was bad. It seemed like some of the comments were heading in the right direction to address my problem, but never quite got there.

Again, thanks for everyone's help.