Bad Engine? -- Now with video! -- Update

I have been working on and off on my KZ750 for the last 10 years or so and just can't get the bike to idle. This past weekend I cheated and took the carbs off my bike and put them in my brother-in-laws bike ('80 KZ750H1 that I used to own) and the bike idle nicely with my carbs in place! So, it appears to be not carb related.
I just checked the carb boots, adjusted the valves, lubed the advancer, checked the cam-chain tensioner, did a compression test (cold with carbs off, all were ~120psi), carb sync (~20cm vacuum) and such. I have checked the coils and ignition coils and they have the proper resistance. I checked the cam-chain for wear a while ago and it was in spec. The bike has less than 20,000 miles on it and my brother-in-law and I have a UNI foam air filter, stock air box, stock jetting and a Vance and Hines 4 into 1.
I have yet to do the coil relay mod and I am planning to do it.
So, can it just be a bad motor? I would appreciate any thoughts. Ask for more information if you need it.

Post edited by: cafekz750, at: 2007/06/20 07:37

Post edited by: cafekz750, at: 2007/06/20 16:27

I doubt on a bad engine, no such thing unless the cylinders are like ovals and the camshafts have circular lobes. Follow your mind on coils.

I wouldnt think a bad motor, prob just some minor adj, could be as much as cam chain stretch which has moved the valve timing a bit, or something simple as a very minor vacum leak that you just havent located

i think you still might just plain have the valve timing screwed up.
how does it idle?
choppy like only on two cylinders?
have you done the water on pipes test?
do you have a auto or manual cam chain tensioner?
just because coil resistance is in spec don't mean they are getting power.
i found loose terminals on my right coil and it drove me batty till i found it.
keep us posted.

btw, please put your location in your signature line.
maybe there is a member close to you who might be able to offer some help.

Post edited by: kawsakiman, at: 2007/06/18 20:07

cafekz750 wrote:

...can't get the bike to idle... Ask for more information if you need it.

As suggested by kawasakiman, could you elaborate on inability to idle. For example, does it fluctuate or just die below a certain rpm and what is the current lowest rpm for stable running, etc.?

May help in diagnosing the problem.

I captured some video which I hope will be better than my description of what's happening with the bike.

1. The bike runs better when cold and becomes worse (won't idle) after it is warmed up.
2. The idle wanders around between 1200 and 2000 when the bike chooses to idle.
3. The bike runs worse when it is warmer outside.
4. I have to play with the throttle to keep it running at a light.
5. The bike doesn't sound like it is running on all 4 at idle. There is alot of chatter and a lumpiness to the bike.

The video is after a 40 mile ride and I am using the throttle to keep the bike idling. There is a bit of wander with the forced idle.

video of idle trouble
<object width="480" height="385"><param name="movie" value=" www.youtube.com/v/L4taqaZfK9k&hl=en_US&fs=1& "> www.youtube.com/v/L4taqaZfK9k&hl=en_US&fs=1& " type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="480" height="385">

Please ask away. Demand photos, more video and such! I would like to track this problem down. My wife has coined the bike "the holy grail" since I have for the past 10 years said, "I think I found the problem..."

Sounds like you got a wicked loose cam chain or a bad valve, way to much clearance on the shims...you need to find out what that rattle is soon...even if it dropped a cylinder or two it should not rattle like that...

1045

Way too cool. Engine diagnosis on a worldwide Kz site using a homemade video posted on Youtube.

Gotta say that the varied uses of today's Internet technology like this is pretty cool.

Cheers-Colin Firth-Ontario Canada

This spring I checked the valve clearence and only had to adjust one valve.
The specs for the engine are 0.003-0.007". The exhaust is 0.006" for all 4 and the intake are 0.004". I currently have a automatic cam-chain tensioner on the bike.
When I re-installed the tensioner after the valve work, I turned the engine over to make sure the tensioner was working correctly. Not to say that it could have stopped working after I started the bike.
The bike does seem to be running worse than it did when I first put it all back together. Would a person measure the cam-chain again? What about a manual tensioner like the one a Z1?
I would really like to find the problem.

Post edited by: cafekz750, at: 2007/06/20 09:52

The noise might not be that bad. Might just be because two cylinders are not firing. Go out to an old Chevy truck and pull a few of the plug wires off and see how it sounds. It will sound about the same. The bike sounded ok when you reved it up a bit. Can you get a video of the engine reving up to around 6000 or so. Video the engine, not the tach so we can hear it better. You can also get hold a hose up to your ear and stick the other end around various parts of the motor. You should be able to tell where the noise is coming from. Do this before you rev it up too much just incase it is a bad cam chain or bent valve.

I'm on the Very Very sloppy cam chain page. I think if it were a bad (broken) valve, it wouldn't rev so well! Just my $ 0.02 worth.

Does the cam chain tensioner have a lock bolt/screw? Is it functioning correctly? does the cam chain run over some form of metal/rubber guide inside the engine (like the kz900 does)? Could this be worn out or broken?

Good luck.