Smoke from under engine?

I'm having 2 problems (2 that I've found) with my 1982 XJ750J. The bike has been sitting for about 2 months.

1) After running (even at idle) for a couple minutes, smoke starts to come from under the bike near the oil pan/collector. I'm not sure if this is the exact location because I can't find where it comes from exactly.

There doesn't seem to be any leaks on the engine that I can find.

2) Whenever I blip the throttle to above 3k rpm, the rpms just stay there and don't come down. Sometimes they come down while riding. I don't think it's a stuck throttle cable since I can see the throttle shaft close on the carbs when the bike is not on.

I tried spraying WD-40 around the boots for intake and out of the carbs but I didn't see a change in the RPM so not sure if it's a vacuum leak either. Where else could there be a leak?

I plan on cleaning the carbs for the first time this weekend (I've only had the bike for 4 months) to see if there's a clogged jet.

 

Have you checked the oil level as you have recently got the bike? Are you sure it is smoke and not water vapour? Let the engine and exhaust get up to operating temperature as it has been sitting to see if it stops could be dampness in the exhaust collector. How far did you run the bike? Was the bike stored inside or outside?

 

Thanks for the response. Oil levels look good, I'm going to change it this weekend though.

How can I check if its water vapor vs smoke?

I ran the bike for about 2 miles (10 minutes ish) and a few minutes in the garage at idle. The bike was stored inside.

I'm not even sure if the smoke is coming from the exhaust or the engine, is there a way I can check that as well?

 

For the hanging throttle - have you done a running synch on the carbs lately?

 

I have not. I'm buying a carb synch tool as well to try that out. Just curious, how would an out of sync carbs affect this?

 

Water vapor will be white in color with very little to no odor and will dissipate much more quickly than oil smoke. Smoke will last longer, oil smoke will smell and generally is blue-ish. Smoke from an overly rich burning engine will be blacker in color and have a heavier gasoline like odor.
John

 

Thank you for the explanation.
Hmm it does not have a strong smell and it is white as far as I can tell. Should it eventually go away if it is water vapor?

I'm not sure how burned oil should smell.

 

If it is water a hot exhaust system will dry it out that's why it is better if the engine and exhaust are at operating temperature or fully warmed up.

Oil burning off happens when an engine has been rebuilt because the oil used to lubricate the cylinders is burned when the engine is started up. This is temporary. If a four stroke engine is always burning oil there is a problem with the oil control rings letting oil into the combustion chamber. This can also happen with worn valve stem oil seals. The most likely cause is water in the exhaust boiling off. Don't be concerned about oil at the moment. Let the engine run till it is hot to see if the steam l will call it disappears.

 

Got it, I'll let it idle for a couple minutes and see what happens. Out of curiosity, where would water have gotten into the exhaust system? It's been in the garage and it's air cooled.

 

Condensation when a hot exhaust is cooling down and there is water created during the combustion process. I would let it idle for half an hour. Exhaust systems rot from the inside out as combustion creates a situation where the metal can corrode although this takes a long time. Carbon dioxide and water are a by product of combustion in internal combustion engines.

 

there is a little hole on the bottom of the exhusst it is a drain see if yours is clogged up

 

Is it the small hole where the exhaust meets the collector? I can feel exhaust air coming out from there when the bike is running.

 

yes thats where water should drain. I would imagin the bike has to be on the centerstand for it to work correctly. if you feel exhaust coming out the holes are clear

 

Any oil that has seeped out of anywhere, like shift shaft, crank shaft seals, valve cover gasket, etc......will run down to the bottom side of the engine and the top of the exhaust.if it’s just sitting then when the engine is fired up, get hot, it will burn off, too.

 

Interesting. This is what I suspected as well. But I can't seem to see any oil leaks anywhere or an oil build up.

I saw that you can use baby powder to find oil leaks? Is that a good idea?

 

Sump plug washer any oil leakage from it? Or the oil filter or oil cooler housing O ring?

 

So update:

I pulled and cleaned the carbs (for the first time). It wasn't as complicated as I was aniticipating (except for when I installed the floats upside down the first time haha)

But one the jets in the carbs was wrong, instead of a #43 it had a #40. This could a cause of a lean mixture correct, causing the high rev issue? I have yet to tune since the gunsen is coming from Chacal.

Also, I bench synced the carbs and they were really out of sync. I have to do a proper tune with a gauge but I think you guys were right, they were very out of sync.

I am yet to run it for a while to see the smoke issue.

Thanks ya'll for helping a junior mechanic (20 years old)!

 

You’re getting there

nice to see someone a bit younger learning these, and more importantly— LISTENING to the advise given when asking questions.

Trust this— we have NO problem with ‘asking a million questions” when someone is willing pay attention to the answers

welcome

dfox

 

Dust burns with white smoke too.

 

Ran the bike and did a carb sync. I noticed this puddle which I think is water dropping from the exhaust. So I guess the smoke was from this.

As far as I could tell, there's no more smoke anymore!

I don't have a YICs tool yet so the carb sync didn't make sense but the bike does run better than before. How important is it to get the needles close to each other? Here is how far I could get them.

 

You should do a running sync even if you don't YICs tool. I have one that I used one time. After that I have done the running sync without it and I haven't noticed any difference. A lot of folks never use the YICs tool.

 

My sync stick is still in the plastic from when I got it 10 yrs or more ago.

gauge needles.......I’d try to get 1 and 2 balanced a little more, then bring those inline again with 3/4. If it’s impossible to get it any closer/smoother, then leaving it if it’s running really good now.

 

The YICS tool is not needed. You won't ever be in for emissions testing. A runningsynch wihout will be more than good enough for daily use.

 

I see. I wish I knew this before I bought one locally.

I can try getting it more balanced. I didn't have much luck the first time.

 

In the pic, I see the exhaust weep holes are doing their jobs. Was that water/moisture or was it gas? I am sure you can get that sync a little close for that #1 cylinder.

 

I think it was water. I smelled it and it didn't smell like gas.

Yep gonna try again sometime today to resync

 

I need advice on this one.

The bike sounds fine on the stand and in neutral. But when I ride, it turns off as I pull in the clutch and down shift coming into a stop. I can hear the rpms go low and eventually shut off unless I keep reving as I come to a stop to keep them up. Then it idles fine when stopped. The bike is definitely warmed up since this happens even after 15 minutes of riding.

I tried raising the idle, but that felt like it was doing the hanging idle thing again and just felt like it was over revving every time.

Is this a fuel mixture ratio issue? Or another carb sync?

 

1You might be turning the screw in too much at once— teeny tiny adjustments are what you try to do.

2. Conversely, what happens if you pull the enricher on in teeny tiny amounts?

 

1) Ah I see. Generally, the increasing the idle should help with this right?

2) By "pulling" do you mean using the choke? I haven't tried this, I only used the choke on warm up.

 

1. Well, if the idle is too low it can die. If it’s too high it can race. If you creep up on the speed you like, you have a better chance of getting where you like it than if you just crank the screw in a couple turns or farther out a couple turns. These are sensitive to small changes, so don’t make big changes at once.

2.when the bike is running and warmed up as you described; and the idle speed starts dropping and heads toward dying, as you described, what happens if you start pulling the enricher back on in teeny tiny amounts, as I described?

You have a lever on your left hand control for the enricher. As you PULL. The lever it tightens a cable which opens the enricher plungers. This allows extra fuel in. Normally it’s used to start a cold engine by pulling it pretty much all the way on. But, if you’re having this issue and adding a TINY bit (or couple tiny bits more) of enricher bring the RPM’s back up to where you want it, then you need to look at your carbs again since that’s an indicator of still-clogged passages.

 

1) That makes sense. Going to try it when it warms up outside.

2) Haven't messed with it enrichment while riding yet, but will do next time.

I did change the original jets which were #40 to #43 since the manual stated #43 for stock jets. This should make the mixture more rich right? Could this be affecting it?

 

Are you making sure that the engine is warm enough to ride without enrichment before pulling away?
A cold engine will die very easily, especially when coming to a stop.

 

Yes, as far as I can tell it's warmed up.

This even happens 10 minutes into riding when it should be pretty warm. I haven't had a chance to test it since it's getting to be really cold the next few days.