smoke screen at higher RPMs

Hey guys,
I recently got my hands on a 1980 KZ 750LTD H1, It runs pretty well, however when I get her up into the higher RPMs (around 8-8.5k) theres some exaust smoke and if she goes anywhere near the red (9k) there is usually a pop followed by a smoke cloud that would make James Bond's Aston Martin's smokescreen jealous.

The oil seems to be coming from some connector that has two hose connectors and a breather on it that sits right above the airbox. At the higher RPMs the oil is leaking from the breather into the airbox which I assume is making my smokescreen. The oil leak is pretty bad after taking it up that high, however if I let the bike cool down and clean up any leaked oil it will run fine afterwards.

Im going to test the compression sometime this week to see how its running.

Also it is idling pretty high and I know the carb's need to be synced (also getting done this week) I don't know if this would have anything to do with it but just trying to give as much info as possible.

The bike runs quite well around town at speeds less than 80, but I'm hesitant to get her on the freeway with this problem.

Any help/thoughts/ideas would be appreciated, I'm new to working on bikes but I'm trying to learn (so bear with me if my terminology/knowledge is'nt perfect)!

I just went outside and noticed the number 1 exhaust was running cool (able to be touched) so at this point I'm thinking I need a valve job, any other thoughts?

Is you oil level too high?

I think the compression test is a great idea.If you come in low, try adding some oil into the cylinder and retest.If you compression goes up then the rings in that cylinder are likely bad.

the oil level is def. not too high, there seems to be the leak at the high end rpms and a gradual leak, so keeping the oil level high is a futile attempt at best right now

ill post the compression numbers and results as soon as i get it done, is there any chance that the carbs being so out of sync could have anything to do with it?

Always.

I think you have a great blueprint laid out to find that problem.

You seem to have two problems... one cylnder isn't firing and the emissions control system is malfunctioning somehow...

The cylinder not firing? This problem should be addressed first, in my opinion. Since you seem to have jumped on the bike without doing any tune up, keep in mind the problem might be compression, ignition or fuel. START by checking the compression for each cylinder. Remember to keep the throttle open while you check. You would probably do well to repeat the compession check with a teaspoon of oil down the plug cylinder and record readings for both tests. The oil test will indicate whether the problem is rings or cylinder bore rounding or by inference, valves. Once this is done, check valve clearances; especially where any compression reading was low. DO NOT SKIP THIS STEP.

Next, if you have not fixed the mis-firing cylinder problem by the valve adjustment, start checking the ignition by swapping the #1 and #4 plug wires which are connected to the SAME COIL as they fire at the same time. If the problem MOVES to the #4 cylinder, then the plug wire, plug cap or spark plug are the issue. If the problem stays on #1, the problem may be fuel related. We can go into that if you get this far...

Once you have the plugs all firing, and have already checked compression dry and with the oil, we can look at the smoke issue. If the smoke is coming from the emissions stuff, not sure where it would be picking oil up... I would guess that the crankcase vent is blowing oil up... the vent would like be routed into your airbox and the excess oil is dripping or burning on something hot. The normal reasons for blow-by (oil coming out crank breather) is:

1 oil overfill
2 ring or piston lan cracked
3 ring not installed correctly
4 rings or cylinder bores badly worn

Like I mentioned already, once you have all the cylinders firing, chase the smoke issue...

Ok, here's what I've managed to get done today:
Ran a compression test, the engine was warm but probably could have been ran longer (idled it about 10 mins):
numbers were (in cylinder order): 95 80 70 95

I don't know too much about compression, but i'm pretty sure these aren't good.

Ran again with a few drops of oil and each cylinder went up to between 120-140

I'm not really familiar with valve stuff so I'm going to wait until Monday and have on of my friends who is a mechanical engineer help me out. My Clymer should also be in by then.

I know the carbs def need a good cleaning as they got covered with oil when I got that smoke screen action. And I know they are out of sync so I'm not sure if this could be a contributing factor to the low compression but I'm just trying to give all available info.

I did manage to replace a leaky petcock valve today though with the Suzuki replacement from Z1 (which is the most successful work i've done a bike thus far lol)

Those numbers are pretty low, I hear engines won't run when they are much below 100psi.

I think maybe you did not have the throttle wide open when you did this test?

The oil you are putting into the cylinders is sealing the rings, worn, causing the compression to increase. If the compression did not increase, it means leaky valves. Your engine is creating blowby past the worn rings into the air cleaner box and is sucked into the engine. Unplug the hose from the crankcase and see if the oil smoke decreases. As long as you have the cylinders off, do the valves and oil seals too. chris3

I was holding the throttle open, the engine hadn't been ran in a day or two when I did this and I only let it run for about 10 mins so that could be part of the reason.

The rings obviously have some issues, ill probably get some ring kits and get in there when one of my buddies can help me, how hard is this to do by the way? Where is a good site to buy ring kits?

We're also going to check out the valve clearances, this could be a multi pronged problem with the compression, I'm guessing we'll find some valves that need adjustment and if I'm thinking right this might solve some problems and then if I have the rings done hopefully she'll be running much better.

The valve adjustments should be done on Monday so Ill post the results then. Any advice in the meantime?

Also, its hard to judge the smoke because its only when I'm riding and at high RPMs, even if I rev it high just sitting there, no smoke. The engine seems to be running very strong in the lower RPMs (below 8.5k) despite the low compression

Post edited by: k0pper, at: 2007/07/28 09:57

A misfiring cylinder will put extra pressure into the crankcase past the rings, causing extra blow-by. Valves that don't quite close will cause low compression, causing misfire, causing fuel to wash-down the cylinder, causing the rings to leak. Sitting in a garage for six months will cause low compression until you ride the piss out of it and reseat the rings. Wired is steering you right. Solve one problem, then retest, etc. Make it run right, not just okay, and the blowby may well disappear, taking away your bug-sprayer feature.

You have a smog (EGR) valve located under the tank.
When the get old they quit working.

Do like me and every one else does...

Remove the valve and both big hoses.
Follow the small vacuum hose to the carbs and
remove it. Put a rubber cap in is place.

Remove the big hose from the bottom of the EGR
valve where it goes into the air box. Plug the
hole.

Run a hose from the left valve cover over to
the right valve cover.

Drain the oil and return it to proper level.

Now go ride it....BIG DIFFERENCE...

Bob