KZ 750 H3 - Valves and Compression

(First of all, this is not REALLY my first post, I had a KZ400 cafe waaaaay back when and used to frequent this site...)

I just picked up a KZ750 LTD\H3 that sat indoors for the last 7 years. Typical "It ran when parked" story... I have come to doubt that, as there was a bad motor ground, and the wiring for the starter switch itself was bad.

Anyway, I have cleaned the carbs very well, the tank is clean, petcock works, and I fixed all the electrics.

There is 25k on it.

My cold compression is not good. I am reading 120-30-10-110. These are awful numbers, obviously. Of note is that the intake side pulls air hard, all about the same (judging with my hand) from all four.

I added 2-stroke oil to the cylinders and saw no change in compression. So, I should assume it is not rings, correct?

So, I ran the bike anyway. No awful noises, and I have gotten it to run, at least as well is to be expected. It would seem the 10PSI cylinder is not firing (stays cold... I wonder why :laugh:) - After getting the bike hot, there is still no change in compression. I was hoping the stuck valve(s) might free themselves.

I was thinking about dumping seafoam in the breather(s) above the exhaust cam. Worth a shot?

The real point is to ask what the PROPER way of fixing this is, or at least investigating what's wrong. I really am dreading dealing with a cam chain, buckets, shims, ugh...

What's the procedure and clearance for valves?

It sounds like a valve adjustment is in the cards for you. It sounds daunting, but it's not too difficult. There are numerous threads on how to adjust valves, so to keep it simple I will refer you to the search feature. Search the "KZ Information/Filebase" tabs at the top of the forum, I think some tips are there.

WBPDX wrote:

...what the PROPER way of fixing this is, or at least investigating what's wrong. I really am dreading dealing with a cam chain, buckets, shims....

Would first remove the valve cover and measure the valve clearances, to determine which of the under-bucket shims may need changing. The measuring of existing clearances is relatively quick and easy compared to the process of changing out shims.

If clearances are found within specs, the poor compression is likely attributable to something else, such as burnt or damaged valve and/or seat preventing closure, or a valve spring issue, or leaking head gasket, or piston/rings/bore.

As known, it's the actual "changing" of under-bucket shims that requires removing the cams to access. On the bright side, once adjusted, the clearances should remain in specs for quite a long time.

I concur with suggestions of OKC_Kent about reading up on the procedure. Especially about correct re-assembly, and how best to avoid stripping out threads in the cam bolt holes.

Good Luck!

WBPDX wrote:

...KZ750 LTD\H3 that sat indoors for the last 7 years...25k...120-30-10-110...intake side pulls air hard, all about the same (judging with my hand) from all four.
I added 2-stroke oil to the cylinders and saw no change in compression. So, I should assume it is not rings, correct?
So, I ran the bike anyway. No awful noises, and I have gotten it to run, at least as well is to be expected. It would seem the 10PSI cylinder is not firing...bike hot, there is still no change in compression. I was hoping the stuck valve(s) might free themselves. I was thinking about dumping seafoam in the breather(s) above the exhaust cam. Worth a shot?...

I would do a leakdown test (on every cylinder), which could prove very helpful in the diagnosis, by pointing to source of compression loss.

At relatively low 25K miles, valve clearances might never have been checked; but pistons/rings may be okay.

Some Seafoam in breather above exhaust cam shouldn't hurt anything (but doubt it will help much).

Am unfamiliar with mechanics of the breather apparatus, but wondering if there could be some fault in it causing the low compression where intake side pulls air hard, all about the same (judging with my hand) from all four.

Is 10psi cyl getting good quality plug spark?

Good Luck!

Actually, the 10PSI cylinder is getting the weakest spark. I might have seen some evidence of frame grounding, so I'll chase that down today as well. I'm sure I'll be tearing into the carbs once more before this is all over... And really, I can't imagine even changing the shims is worse than getting those effin' carbs in and out of there!

I'll measure the valve clearances this AM and report back.

Know what you mean about the carbs. Best thing I've done is buy new carb boots. Still not fun but trying to heat up the old ones to get them back on the carbs was a pain.

Yeah, new carb boots are in order if I get the compression figured out...

I have searched and searched, but I can't find:

- A procedure for checking or changing the valve shims for the FOURs.

- A source for the valve shims for the FOURs.

Everything seems to be for the Twins. Can anyone help me out? I just read through about 40 threads dating back to 2006.

WBPDX wrote:

...be tearing into the carbs once more before this is all over...can't imagine even changing the shims is worse than getting those effin' carbs in and out of there!....

Would defer further carb concerns until after addressing the compression issue and any ignition issue. The carbs may be okay, and even perfect carbs can't compensate for problems in the other components such as poor compression.

Drat! Z1E shows "Temporarily out of stock."
All the more reason to hold off on carbs.:lol:

Sometimes automobile parts stores such as AutoZone routinely loan test equipment. Maybe a leakdown tester could be borrowed. No harm in asking.

Good Luck!

try doing a search for 650's, same thing.

Thanks for the info. I have visited Z1E a few times when I lived in NY, I even wrote a paper for college about his business :laugh:

Anyway, the bike is running significantly better on PRI than ON, so maybe the petcock isn't working as well as I thought. The 'dead' cylinder comes on at high revs it seems; after holding it around 5k, the cold pipe warmed up. That got me thinking I may have a carb issue as well...

I rechecked compression after getting her nice and hot, and now returned:

120-60-45-110

Obviously the previously 'dead' cylinder came WAY up.

My plugs are reading lean on the 120 and 60 psi cylinders, so it looks like I'll be tearing into the carbs again anyway...

Is there another source for the shims other than Z1E?

Before you go wasting any more time on the carbs,,, they do not have anything to do with compression, my guess is valves out of adj, or the head gasket is blown,
you have got to get the compression issue fixed first, then work on the carbs to get them jetted correctly, anything you are doing now will have to be redone once the compression is up where it should be

Fair, but I do need to tear into them again, as the 120psi cylinder is lean. I know that the carbs and compression are unrelated. This isn't my first non-running-bike-project, or second, or 10th :laugh:

Also, I have a main jet that was wrecked on removal that I have ordered, and need to replace. I put the wrecked one back in the carbs to see if I could get it to idle.

I'll still check the valve clearances, I promise :laugh: