Oil fouled plug and low compression

I searched the current forums and didn't see anything on oil fouled spark plugs (and the archive doesn't appear to have a search function anymore...)

My #4 spark plug is heavily fouled with oil and smoke comes out the respective exhaust pipe after the motor warms up.

Here are the results of a compression test:

#1: 95 psi
#2: 100 psi
#3: 89 psi
#4: 81 psi

I need to tune the whole thing up, but I figured the oil fouling was due to something a little more serious than valve clearance or weak plugs.

What steps do I need to take to determine what's causing the fuel getting into the cylinder? I know the head was replaced, but I have no idea if they used the old rings (the work was done before I bought the bike). There's no external oil leaks around the #3 or #4 cylinders.

Thanks for any tips!

Post edited by: russbernhardt, at: 2006/05/23 23:29

The search Function in the archives is at the top, right below where it says "KzRiders.com" at the top left.

You have seriously low compression, how many miles are on the bike?
Check valve clearance, as a lack of clearance can kill the compression.
Oil burning is either bad valve guides or bad rings/cylinder bore, the oil burning combined with the low compression leads me to suspect you are going to need new rings (at a minimum).

You could do a leakdown test and find out where your compression is going.

Post edited by: steell, at: 2006/05/23 23:50

I'll double check the archives, but I could swear I didn't see the search link (I've used it before...)

I'll adjust my valves and see if that helps the compression any (if at least to get the other cylinders in spec). From my understanding these are shim-under-buckets, right? Where's a good place online to pick up a shim kit?

The engine has at least 66K miles (I rode it for maybe 100 or so miles with a broken speedo cable, but 66k is about right).

The "new" head has about 7k on it, but again, I have no idea what was re-used. (I know the head was a recent addition when I bought the bike because it was really clean).

I'll probably end up just taking it in and letting the mechanic deal with it, but at the very least I can perform a tune-up.

And here I thought the bike was running great...this thing must really be quick when it's running properly!

KZ750 twin in good condition with a 8.5:1 compression ratio will have 160-170 psi of compression.

Your compression test was done with the engine warm and the throttle held wide open, right?

I just checked buykawasaki.com to make sure, and it shows the shims on top of the buckets.

I thought that was the case, but I wanted to make sure.

Post edited by: steell, at: 2006/05/24 00:48

Hm...no, I did the test cold and I couldn't hold the throttle open because of the crappy gauge I have and a broken starter button (I have to use a screwdriver to start my bike...I like to call it my "anti-theft device").

I guess I'd better re-take the test...although I do hear ticking sounds from the valves when the engine is running, so I'm sure the valves are way out of spec...

I wondered about that when you mentioned how much power it had with those low numbers

I have comparison tested several bikes, and there is a consistant 10-15 psi difference between testing warm and cold, but testing with the throttle closed is totally different, they were all over the map (comparing bike to bike), so testing with the throttle other than wide opem makes the numbers useless.

Russ, You will likely want to change your intake manifolds anyway, so remove the carburetors and repeat the compression test. The MOST likely reason for lower compression on a "new to you" bike is that either the rings are stickey from the bike sitting OR the valves have no clearance. CHECK VALVE CLEARANCES BEFORE REPEATING THE COMPRESSION TEST. I strongly suggest you adjust the valve clearances to bring them within spec before repeating yor compression tests. This will allow you to get a more realistic view of the condition of the ring seat. Once the clearances are adjusted, recheck. If you still have low compression, then put a teaspoon of Yamaha Ring Free down each cylinder and recheck. If the compression spikes up very significantly, the rings are not sealing. Let the Ring Free sit overnight and then recheck as the rings may just be bound up.

Verifying this stuff and not trying to work on other tuning stuff at this point will save you tons of time!

What you see as "oil fouling" may not be oil but just plain poor combustion caused by the bad compression which is very likely the valves needing some clearance. If they stick open, you will have the exact symptoms you describe.

Normal compression on a cop bike J engine is between 140-150 psi I beleive with about 10 psi difference between cylinders acceptable. You had best consult a manual to confirm as this is from memory. Also, your initial compression readings were most likely bogus from not holding the throttle open as you probably wouldn't get the engine running at all with such low compression.

I'll pull the carbs and adjust the valves before I do another compression test. It would be great if the valves are the only problem, but we'll see. How important is it to have the bike warm when doing the compression tests? Should I replace the carbs and run the bike to get it warm before retesting?

The bike does run (though if it doesn't start on the first try, it'll take a good 5-10 minutes to get it to start on the second try), so I can get it to warm up this time.

Would the poor combustion also result in smoke? If the rings aren't sealing well like you said, would that let oil through?

I only ask because I observed the following:

- Smoke coming from right side exhaust which is on #3 and #4

- Ticking sounds in the head sounding like loose valves or something

- #4 plug is black and mucky (I'll try to take a pic later today and post it)

- I lose about 1 qt of oil in a month (there is a small leak that I've been working on, but it's not leaking 1 qt a month's worth!)

From all this I figured I was burning oil, but I'll do the valves and recheck the compression and I can go from there.

Thanks for the tips. Certainly helps!

Like I said above, the temp is not critical, so you don't have to warm it up first, the compression will just be 10-15 psi lower than it would be if it was warm, that's been consistant across the six or seven bikes I have tested both warm and cold. But it is critical that the throttle be wide open (or carbs removed if you prefer).

I seldom bother to check a bike warm. I dislike pulling plugs when the bike is warm and the difference isn't very significant as Steve pointed out. It will be significant if you have the carbs installed and don't open the throttle.

Russ, in the past few weeks, I have had about a half dozen older Kawasakis darken my door where the owners have brought in their bike. ALL thought they had carb problems for the most part as their bikes were all pretty much hard to start and had plug fouling problems and other problems of the same ilk. ALL had poor compression in one or more cylinders. All had lack of valve clearance issues... bikes newly acquired or the clearances ignored. Once the valves were adjusted, compression was good and it was possible to start addressing other issues, like the carbs and such.

I used to put down in my trouble shooting list as the first step compression check but am really tending to think a new bike owner should just adjust valve clearances and then check compression. See... I am capable of learning even at MY advanced age hehe

Yeah, seems like everything gets blamed on carbs

My personal method is:

(1) check/adjust valves
(2) compression check
(3) ignition check
(4) insure fuel is getting to the carbs
(5) if everything else is right, then I start on the carbs.

wiredgeorge wrote:

I used to put down in my trouble shooting list as the first step compression check but am really tending to think a new bike owner should just adjust valve clearances and then check compression. See... I am capable of learning even at MY advanced age hehe

Hahah! Never too late, eh?

I totally missed steell's mentioning the irrelevance of motor temp, sorry! That is good news though as it means less work (i.e., warming the bike, pulling the carbs, adjusting the valves, replacing the carbs, warming the bike again, remove the carbs, test compression).

I'll have to work on it this afternoon and see what's up, though I doubt I'd actually get anything done (finals week in college, you see).

Thanks for the clarifications. I'll be sure to post results.