By Joe Gresh
If you’ve been keeping up with us here at ExhaustNotes you’ll know I had a lot of trouble getting Zed, my 1975 Kawasaki Z1 900, running correctly.
In between rebuilding the carbs and tinkering with most everything I could think of it dawned on me that maybe the engine was just tired. After all, it wouldn’t be unusual for a 50-year-old, air-cooled engine to wear out after 46,000 miles.
I used to have a nice compression tester that was at least 40 years old. In the big move west I can’t seem to find it. Maybe it got tossed after one of the many floods that inundated our house in the Florida Keys. I forget the brand but it had a flex hose and several adaptors for different size spark plugs.
I don’t need a pro-level compression tester as I’m not in the mechanical business anymore. This cheap, cheerful Yonligonju (say it three times fast!) Chinese kit on Amazon looked like the goods for less than 20 dollars.
The Yonligonju comes with a nice, blow molded plastic case that keeps all the little bits in order.
It amazes me how China can build such a nice kit for so little money. Including the quick release flex hose, this kit comes with adaptors to fit 5 different spark plug sizes.
In addition, the set came with two of the rubber bung type connectors. To use these, you just hold the compression tester tightly in the spark plug hole. It speeds things up on a multi cylinder engine. This works well enough if you’ve got enough hands for the job.
My Yonligonju worked well, showing 80-ish psi on all four Kawasaki cylinders. This isn’t great compression but the cylinder pressures were nearly even and Zed might have done better if the engine wasn’t cold. My Kawasaki manual claims 85 psi as the lower limit and Zed may get there warm. What do you want after 46,000 miles?
Besides compression, what you’re looking for with a compression tester is one cylinder being much lower than the others. This indicates a problem in the cylinder. The actual psi number is less important. Unless they are all really low…
Anyway, the Yonligonju gauge proved compression wasn’t the reason my Kawasaki was fouling plugs. See the latest Zed update for the full story.
The compression gauge held the reading without bleeding off for the few minutes it took me to look at it. There’s a pressure release valve on the side of the gauge that also worked as it should.
This isn’t a kit that will see a lot of usage. If you’re like me, a home-shop tinkerer, the thing will do the job for not much money. Hell, just taking your bike to a motorcycle shop once to test the compression would cost five times what the tool cost.
I think people rebuild old motorcycle engines more than is needed. Two-strokes especially get the piston, ring and bore because it’s so easy to do. Most likely the bike would have run fine the way it was.
For classic bikes that don’t see everyday use it’s enough that the engine runs well. There’s no need for a ton of compression with today’s crappy fuel anyway. I’m guessing the Yonligonju will last a while sitting in my toolbox waiting for another engine to test.
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Thanks for the continuing education Joe. If my Tiger ever starts showing its age I’ll have the ExhaustNotes archives to refer to for help.
That’s a nifty article.
I am wondering what’s your next step in chasing down the fouling issue.?
Do all four of your plugs look the same?
Are they fouled with soot or oil?
80 lbs across the board might seem ok
But it’s less than the 85 minimum kawi specifies.
So I wonder if low ish compression can complicate a good clean burn .
What are u using for gas?
Inquiring,
There’s a story one here about the issues. I forget the title but the Cliff’s notes version is I installed bad aftermarket parts which set me off on a wild goose chase.
Zed is running pretty well now.
Did those “bad aftermarket parts” come from China , by any chance ?
Everything comes from China.
Can you provide a link to the “whole story”
It’s under Zed’s not Dead in resurrections.
It would be a lot more accurate if you did it correctly
Warm engine, throttle wide open, valves adjusted to spec
Joe, how does the zed feel with only 80psi? Also, unless the tester has a schrader valve at the end of the hose (closest to the spark plug hole), the hose volume adds to the cylinder volume thus lowering the compression reading. Your valve is up at the gauge so this will lower your reading. How much I can’t say.
Marcus,
It seems to run fine. Pulls hard on acceleration, revs out through the gears. Gets 50mpg. With 86 octane the low compression doesn’t seem to be a problem.
I’m tempted to pull it apart, give the bores a light hone and put in new rings but I’d probably mess it up for little gain.
A bore scope may show you need or maybe don’t need a hone but my technique is this.. if I don’t feel like tearing down the engine, I don’t check it and simply imagine the hone is just fine. If at some point you need to take the engine apart by all means address the cylinders. But thanks for your answer.