KZ650 - New project, diagnosing engine issues...

Hello everybody - new member here, just picked up a KZ650 last week!

The previous owner was an electrician and got the bike as payment from a friend that he did some work for. Long story short, the guy played around with the carbs a bit and decided he didn't want to bother with a project bike after all.

I spotted his ad on craigslist, and went to check it out a few hours later. The bike seems pretty solid so I gave him a few bucks and threw it on the trailer.

I got it home and had it running within a half hour... not really sure what I did to fix it... it had air, fuel, and spark when I checked. After I gave it the once-over, I cranked it for a while (the bike had been sitting 4 years prior to the last guy getting it) and it fired up after a little coxing.

My first observations:

1) It only ran at full choke, but settled into idle nicely (about 800-1200RPM off the top of my head). Although when revved it felt like it was very rough.

2) After 10-20 minutes of running I was able to turn off the choke, but the idle shot all the way up to 4000RPM+.

3) It was smoking like crazy - especially at idle, but also at high RPM with the choke off... If there were any mice in my garage, they've been fumigated out by now . It seemed to me that it was smoke from running over-rich, although it had a little bit of that oil-burner smell going on too.

Beginning diagnosis:

First, I pulled the plugs and EVERY PLUG was covered in what appears to be motor oil... the spark plugs look brand new and on all four cylinders the ends are very dark brown/black and still wet when I got the plug out. Should have taken a picture, but I didn't think of it at the time.

My first reaction was that the rings/walls are worn and it's getting oil blow-by into the cylinders.

So this morning I went and grabbed a compression tester:

#1 - 158
#2 - 150
#3 - 158
#4 - 140

...those numbers don't look terribly bad to me?


So now I'm at a little bit of a loss. Assuming it is engine oil I'm finding on the plugs, how is it getting there? It seems strange that it's in all four cylinders.. can it be getting in through the valves? Bad timing? Worn valvetrain?

If the top end was worn that badly though, wouldn't I be getting worse compression numbers?


If anyone's got suggestions I'm all ears!

Thanks - Kevin

EDIT: I should note, it's a 1978 KZ650 B2(?) model I believe. It has approx 13,000 miles on the odometer and looks to be in pretty good shape - no external leaks of any kind and very little rust/pitting; appears to have been garaged most, if not all of it's life. Thanks again!

The oil could have been squirted into each cylinder by the PO and was letting it soak before attempting a first start. But of course, he was never able to start it. Your compression numbers are good enough. Although, 140 from lowest to 158 highest is a bit out of range. Should be no more than 14 psi between lowest and highest. Having said that, the rings may be stuck on on the lower cylinder and the compression may come up on that one after a bit of riding. Mine did. The oil could also be due to valve oil seals. But that usually burns away after a minute or two. As for the idle, I would take the carb rack off and give the pilot circuits a good cleaning. Once you reinstall the carbs, make sure they are seated in the boots correctly should confirm there are no cracks in the intake boots prior to installing them. If you still get high idle when you try it again, check for vacuum leaks. Would check the idle before putting the throttle cable back on. You can check for leaks by using either starting fluid, or carb cleaner or an unlit butane torch around the intake boots and look for any changes in the rpm's. You should have some type air cleaner installed when check everything out.

Nice find.
Do you have a repair or factory service manual that covers this year and model bike.
Compression looks good.
Can you upload pics of the plugs?
Sounds like a carb rebuild,idle circuit seems plugged.
Using your manual I'd start with checking valve lash,even thou compression is good you have 1 cylinder that is little weak.
Then go over the ignition followed buy 4 new plugs but, before you fire it up rebuild your carbs to factory specs for a good baseline.

Thanks guys!

I have a Clymer manual and 4 new plugs in the mail already

They should arrive sometime early next week along with a few oil filters and a new air filter. I was suspecting a carb rebuild even before I found the oil in the cylinders, so I'll get some of those kits on their way as well.

I'll throw the tank back on tomorrow and fire it up for a few minutes to get some pics of the plugs.

Going to have to read up on the ignition system.. not familiar with the older "points" type. The Dyna seems to be a pretty popular upgrade from what I'm seeing?

As for the carb boots - what's your opinions on a touch of black RTV on the mating surfaces when I reassemble? Seems like it might not hurt if that's a common weak point.

Cheers - Kevin

Here's a shot of the bike, just for kicks:



And as it sits now:



And lastly, I'm aiming for something along these lines:

thebikeshed.cc/2013/02/13/la-corona-3/

Thanks again!

A lite film of rvt wouddn't hurt and that is the only place on a small engine it should be.
But new carb and air box boot would be best.

.

Hopefully the previous owner stored it correctly and that explains why she starts AND smokes after a long sit. I would go through the carbs just so you know they are good, drain the tank and clean it real good before you start the bike after carb cleaning. That will take care of fuel delivery. Then start her up and see if anything changes. I would check the points to make sure they are worthy. I would not start messing with the ignition until you know fuel delivery is right. The point system will work to get the bugs worked out then go for the dyna for piece of mind. Since it is running you just have to tweek and verify all systems complete. I hope you do not have a ring/valve train problem. The carbs need to be right so you can diagnose other systems. Good Luck and have fun with it

If it only runs on choke then the carbs are dirty and plugged up from old gas. Take the carbs apart and clean them pay extra attention to the idle circuit passagways. Make sure all the small passagways are clear.
Do not use RTV on the manifolds use yamabond or something similiar. RTV will eventually break down and you end up with another leak.
If it runs only on full choke then a plug reading will be usless.
Nice bike after a little work you will have a nice looking ride.

Don't know what happened here but I clicked on submit and it posted more than one.

Cleaning the tank while I wait for the carb kits - thanks again everybody