My first project

[stevestrom]

Not necessarily; to get enough blow-by for smoke out the breather, generally all three rings on a piston need to be bad. To get oil into the combustion chamber, only one or two need to not be sealing right.

Another possibility is the 2nd ring is upside down. This is the ring that does the work of removing excess oil off the cylinder wall. Install it wrong, and it'll scrape oil into the combustion chamber.

Oh man, I hope that's not it! I would hate to have to tear it down to that stage again. Especially without having had the chance to ride it. Nothing like doing a job twice!

Here's hoping a few runs on the bike will clear it up and I don't have to tear it down again.

Also, when I pulled the plugs last time I ran it I had smoke coming out of the #1 plug hole (quite a bit!).

[stevestrom]

I am going to be doing a leak down test to find out where the oil is coming from.

Any chance that one of the valve seals could have popped off? I did put new ones on.

I was talking to a friend about it last night and he was with me the first couple of times that I started the bike after the rebuild and niether of us noticed any smoke at that time. Seems strange that it would develop as a problem.

[natemoen]

Anything is possible!

[stevestrom]

Ok, still haven't got the leak down test done (still need to make one). I had a couple of mechanic friends check the bike out and they both figure that its running rich and thats why its smoking. I can smell gas in the crankcase that is not leaking into there while its parked; I always shut the petcocks off. When I pull the carbs the intake boots are wet with gas and the plugs look like this. (cylinders 1-4 ; left to right)



So I pulled the carbs checked the needles and seats for damage and made sure that they sealed, made sure that the floats floated, set the float height to 23MM (they were at 20MM), and then wet set the floats just to be sure.

Put everything back together and I have the same problem, begins to smoke a little a few seconds after startup and then heavier if reved up. I made sure to note all of the jet sizes when I had the carbs apart and they are all stock jets.

I have no intake at the moment and went to a 4-1 header, I was expecting to be lean, not rich. Aside from going with smaller than stock jet does anyone have any ideas on what it could be?

[Ken Talbot]

Yup, something doesn't look quite right. After you checked and set the floats, did you perform a full sync and 'colortune by ear'? If not, that would be a good place to start. In theory, all four plugs should then be the same so you can see if it is still rich or lean overall, or whether the black is coming from burning oil.

[natemoen]

Also, if you are smelling gas in the crankcase get ride of that oil before you spin a bearing.

[foreda]

Tune

Make sure you have a fan on her when dialing in the carbs. This can be a pita. Also, if you used an aftermarket jet kit (don't remember reading this but!!) they can be different in size from the Mikuni Jets. DAMHIK!!

[81xsproject]

So, the first thing I did was go back and look to see if you used carb kits, but it doesn't sound like you did. You did say you replaced the mixture screws because the were rusty...? I thought they were brass? Anyways, where did you get them? How many turns out are they from seated? You said you wet set the floats after setting them to 23mm. Did you have to adjust them from your previously set 23mm when you wet set them. It's just my opinion, but I try to sway people away from wet setting the floats as it is more likely to result in a bad float height than it is to give you something better than a good 'dry-set.' Did you do a good bench sync before installing the carbs? A proper bench sync will not leave a lot of room for improvement by a vacuum sync. Sorry for all the questions you may hove previously covered, just trying to help dig up a rich issue.

[WMarshy]

A little OE... (operator experience)

I read something about someone doing a ring job and they had the gaps in all the rings aligned. They had problems with smoke after their rebuild and it was isolated to one cylinder IIRC. Any chance you did the same? I know the motor might not be broken in fully but you might consider a compression test to see if there is a significant difference between #1 and the rest (anyone know for sure if compression would suffer from this?)... A compression test should be done on a warm engine (but not necessary though) with the throttle wide open. If everything checks out there try getting your F/A mixture dialed in a little and drive the thing, its probably just trying to clear its lungs!! Any idea what your exhaust temps are running at? Maybe weak ignition in combination with over rich? Good luck and nice build!

[cywelchjr]

When I replaced my engine with one from the junkyard, which had been sitting for at LEAST 3 years, it smoked for about 2 weeks after putting it on the road. I went through about 1 1/2 quarts of oil, and then oil consumption dropped pretty much to nothing. I know go through about a cup of oil per oil change. Now, I don't hotrod the bike, and I try to take care of things and use a good quality oil (I've used the diesel rated stuff and it used oil with it, I actually am using Castol MC oil but YMMV) and ride pretty much daily, although it's really most of the time just far enough to get fully warmed up if the weather isn't too cold.

I also used a seal conditioner that has always worked well on me in autos, I just use half the container and treat it once a year. It's supposed to be the same stuff that is in the oil to keep seals from drying out, it just increases the amount for one oil change per year. Seems to have worked well for me so far.

[stevestrom]

So, the first thing I did was go back and look to see if you used carb kits, but it doesn't sound like you did. You did say you replaced the mixture screws because the were rusty...? I thought they were brass? Anyways, where did you get them? How many turns out are they from seated? You said you wet set the floats after setting them to 23mm. Did you have to adjust them from your previously set 23mm when you wet set them. It's just my opinion, but I try to sway people away from wet setting the floats as it is more likely to result in a bad float height than it is to give you something better than a good 'dry-set.' Did you do a good bench sync before installing the carbs? A proper bench sync will not leave a lot of room for improvement by a vacuum sync. Sorry for all the questions you may hove previously covered, just trying to help dig up a rich issue.

The springs around the mixture screws fell to pieces when I took them out they were rusted so badly, not the mixture screws themselves. I did not have to readjust the floats from the 23mm setting when I wet tested them. I may have screwed up the bench sync when I first did it. I re-adjusted it tonight and I'll try it again when I get the carbs back on. Hopefully finetuning the bench sync a little more will solve my problem.
Thanks for the help!

[stevestrom]

Also, if you are smelling gas in the crankcase get ride of that oil before you spin a bearing.

I'll make sure I do!

[stevestrom]

I read something about someone doing a ring job and they had the gaps in all the rings aligned. They had problems with smoke after their rebuild and it was isolated to one cylinder IIRC. Any chance you did the same? I know the motor might not be broken in fully but you might consider a compression test to see if there is a significant difference between #1 and the rest (anyone know for sure if compression would suffer from this?)... A compression test should be done on a warm engine (but not necessary though) with the throttle wide open. If everything checks out there try getting your F/A mixture dialed in a little and drive the thing, its probably just trying to clear its lungs!! Any idea what your exhaust temps are running at? Maybe weak ignition in combination with over rich? Good luck and nice build!

Alright, still haven't got around to building a leakdown tester and I don't think I have to now. I borrowed a compression tester from a friend and did a test this evening. I tested the bike cold since it's snowing outside and I didn't want to run it in the garage (also, it has no carbs on it at the moment).

These are the numbers that I got:

Cyl#1 - 100
Cyl#2 - 95
Cyl#3 - 85
Cyl#4 - 103

Do these seem low for an engine where the rings may not be seated yet? Keep in mind that the engine was cold (below freezing) and has not been started in a week or so.

I put some oil into each cylinder and these are the results of the 'wet' tests:

Cyl#1 - 160
Cyl#2 - 175
Cyl#3 - 165
Cyl#4 - 170

So from this I assume that my valves are not the problem but my rings are. I think at this point I am just going to try to fix the rich issue so that I can do a proper break in without washing the cylinders with gas. After the break in period I'll revisit the compression test with a warm engine and see what my numbers are.

Impressions?

[crazy steve]

Well, that definitely shows that the rings aren't sealed yet, so yeah, you need to break-in the motor before you'll get an 'accurate' number.

The good news is all cylinders are within 10% of each other. But I'm curious; did you do anything with the valves? Regrind them, or at least lap them to the seats? Your numbers still seem low even after 'oiling'; I tested a '79 motor with the carbs removed and got compression numbers in the 190 to 205 psi range (without putting any oil in the cylinders). I know the early motors have slightly higher compression and that may account for the difference, but you might also be getting a bit of leakage past the valves.

I've a pair of SG motors (same cams/compression ratio as your XJ), I'll try running tests on them today without carbs and see what I get...

[stevestrom]

Well, that definitely shows that the rings aren't sealed yet, so yeah, you need to break-in the motor before you'll get an 'accurate' number.

The good news is all cylinders are within 10% of each other. But I'm curious; did you do anything with the valves? Regrind them, or at least lap them to the seats? Your numbers still seem low even after 'oiling'; I tested a '79 motor with the carbs removed and got compression numbers in the 190 to 205 psi range (without putting any oil in the cylinders). I know the early motors have slightly higher compression and that may account for the difference, but you might also be getting a bit of leakage past the valves.

I've a pair of SG motors (same cams/compression ratio as your XJ), I'll try running tests on them today without carbs and see what I get...

I just cleaned up the deposits on the valves and seats. I tested the valves for leakage with the head off and they seemed fine so I didn't bother with lapping the valves. Trying to do this on the cheap and I didn't know at that point if the bike would even start!

The numbers you are getting on your engines seems really high, I have little experience with this stuff but from what I have read these engines should be around the 150psi mark when warm. Don't the numbers go up as the pistons expand in the cylinder? I wonder how high your numbers would climb with a hot motor and a little oil?