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Discussion Starter · #1 ·
:confused: Hello - newbee here. Here is what is puzzling me.... About my KZ1000.... Please read the post in it's entirety, as I know that it is a bit confusing...

A little background... I have a 1981 KZ550 LTD, and a 1979 KZ1000 ST.

I got the KZ1000 a month or so ago, cleaned out the carbs, Synchronized them, adjusted the idle screws, decarbonized, etc, etc... The bike runs EXCELLENT ( knocking on wood). 0 - 60 MPH is about 5 seconds ( and perhaps the limiting factor is the rider - me), but 0-60 pretty consistently 5 to 6 seconds. This, based on what I read, is pretty much inline with specs ( is it not?) A valve clearance check I have not yet done....

The bike starts INSTANTLY - cold ( with choke) and warm. I mean, the instant that my finger hits that starter button - VROOM... Also, starts with the FIRST KICK ( again, cold with choke, or warm). It idles smootly, and does not die. If I start riding it right away when cold, I get a little 'popping' until it warms up... No smoke, etc.

OK - now here is what is making me insane... I did a compression check yesterday ( engine warm, throttle held WIDE OPEN and all spark plugs removed) and got 105 110 105 105 compression.... WHAT THE $!*#[email protected]$???

I poured about a teaspoon or so oil directly in the spark plug hole, and did a compression reading ( on once cylinder) again - it jumped to 140 psi... ( previously 105). This normally means worn out rings or carbon build up...

OK - now after this long winded post, here are my questions...

1. Is 105 not too low of a compression???? I belive it is

2. Should I not have some major hard starting issues with compression this low?
3. Should the bike not be sluggish and rough running with this compression?

I am somewhat puzzled... what I see on the compression gague does not coincide with how it is running... Oh, I double checked the compression with a diffent gauge, and obtained the same results... first gague is the "screw in" type, the other is the hold down type... :confused: :confused:
 

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105 seems a bit low. It's possible your comp gage simply reads low. I would suggest doing a compression test on your automobile, if your auto reads much higher, you probably need a re-ring on your KZ.

My GPz1100 reads about 140 psi, and my GS1100 reads about 125 psi
 

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Discussion Starter · #5 ·
Thanks.... The same gauge, when testing the compression on my other bike ( the KZ 550_, reads 180 psi, across all 4.

What I can NOT explain, is, with compression this low, why does it start instantly ( both electric and kick start) and run so good !!! I would expect to have a poor running, smoking, sluggish, hard starting bike with that compression - but it is completely not the case !!! so what gives?
 

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I guess this is the point that someone is supposed to say "Why ask why". :lol: It is low and below specs but I'd say just enjoy it while it last and make the most of it. At the same time I wouldn't plan any cross country trips on it if I were you and to expect to have to do some engine work in the future.
 

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Discussion Starter · #7 ·
Yes :) Sort of a "bummer", but I am on the same page. My masochistic side wants to tear it down and put some new rings in... then the "voice" of common sense kicks in, and asks me WHAT do you hope to gain ????? This is more of a fun bike, and I do not use it for commuting... as long as it runs good, and starts easy, I will keep it as is... of course, it will always bug me to no end, not knowing WHY !!! I will REPEAT ( for the 3rd time !) my compression reading tonight...
 

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You answered your own question :)

You haven't checked/adjusted the valves yet.

Your numbers indicate tight valves, not worn rings. When you do a wet test with worn rings the compression will jump up a bunch, I mean to 170-200 psi. And that's with a dry reading of less than 100.
 

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GHOSTRIDER
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You answered your own question :)

You haven't checked/adjusted the valves yet.

Your numbers indicate tight valves, not worn rings. When you do a wet test with worn rings the compression will jump up a bunch, I mean to 170-200 psi. And that's with a dry reading of less than 100.
+1! You need to check valve clearences. Its routine maintainance on the big fours!
 

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Discussion Starter · #12 ·
Steel - this is the sort of thing I was hoping to hear ( about the numbers indicating tight valves, and not worn rings...). It makes sense, if the compression is to jump to 170-200 psi ( instead of the jump to 140 or so that I saw).... can hardly wait to check / shim....
 

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GHOSTRIDER
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Steel - this is the sort of thing I was hoping to hear ( about the numbers indicating tight valves, and not worn rings...). It makes sense, if the compression is to jump to 170-200 psi ( instead of the jump to 140 or so that I saw).... can hardly wait to check / shim....
Aint no thing! Keep us updated!
 

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Discussion Starter · #14 ·
The RESULTS ARE IN !!!

OK - the results are in....( doing a valve clearance check)...

I could not sleep last night, as all night, kept waiting for the morning to check the valve clearances on the KZ1000 to test the theory of the unexplained low compression.....

Finally, at 5 AM, I could no longer take it - so got out of bed and went at it. I had anticipated some tight valves, but the results proved otherwise. In fact every single one was within spec. ( see below)

Intake:
1. 0.05
2. 0.15
3. 0.11
4. 0.08

Exhaust:
1. 0.15
2. 0.11
3. 0.11
4. 0.10

I checked the cam timing and all seems to be right as well... I put the bike back together, and will be stopping at the Yamaha dealer to buy some Ring Free - don't think it would hurt ( done the sea foam already).

At the end of the day, like someone said.... as long as it runs good, and starts INSTANTLY as it currently does, I will leave good enough alone... unless someone else has some other theories that I can test :)

Thank you all for your help.
 

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Leave it aloan.The comps are a little low. but was the cranking speed fast enough?This can make a huge difference to the readings.I would now adjust the valves to close to the same specs( #1 intake is a bit tight compared to the others & i would reset #2,3,4 exhaust valves to .15 also) Try the ring treatment that you mentioned & ride it two up for a day & go up some big hills to load the engine & get those rings working in the bore.Then do another comp check.Ill bet my lefty that it will be up,& the bike will be going like a cut cat.Keep me posted.Wayno 1500 drifter.
 

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I noticed when I took my car to the Mercedes store recently that they do all the testing with the battery hooked to a charger. I am thinking this is to keep everything at a steady state, so no variation due to low voltage.
 
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