Cylinder compression test - failed ??? :(

Thanks Nebr_Rex. I did do it that the the first time. But I have the carbs off now so I'm guessing throttle is not an issue for now.

I tried renting a compression gauge from Autozone near my house it did not have a 12mm adapter and so it didn't work. Does anyone know some other place that may have this tool for loan? Or I may just have to buy it from someplace, use it and return it for a refund. But not too comfortable doing that.

A lot of the Auto Parts Stores will loan one. An Equipment/ Rental Store would have one in there tool section. Lots of places sell them, Pep Boys, Sears, etc.
Best to get a decent one, just so you can be more sure of the readings. HF one read 20psi low when I tried one, compared to two others I had. I just wanted the adapter in the kit, which did work fine, with my other gauge.

Here are some pictures that I took of my intake valves. 3 of the 4 looked fine but the valve lifter and the valve rod itself look pretty beat up. Any ideas on what's going on here? I still haven't had a chance to get a good compression tester but I was able to temporarily put the carbs back on without the throttle cables plugged in and was able to get the engine started with some starter fluid and the engine seemed to run file on idle. Of course, I'm still working on cleaning/tuning my carbs and replacing the stuck float valve.

In the top picture, it looks like something might be in the port right up on the valve seat. Looking at the picture, there is some sharp edges around what should be the base of the valve seat. There at the Yellow shaded areas.

Yes, there is a problem with one of the harbor freight compression testers. They put the check valve at the gauge end instead of at the spark-plug end.

You don't need a screw-in type. I usually use the hold-in type with the rubber tip. There is not enough pressure to push you off (because the 550's use smaller diameter spark plugs than most KZ's). With the motor cold I would expect numbers in the 120 to 140 range (on a good gauge). Hot will be much better. Most people forget to have the throttle at wide open during the test. As ed said, you want all 4 plugs out too so the starter won't have to work so hard.

If things changed after you did your hand move, then something went into the motor or something moved, that was already in there.

Try to fish it out. Opening the motor is a can of worms for a novice.


If you do anything with the valves, please check the valve train warning in my sig.

loudhvx wrote: ...people forget to have the throttle at wide open during the test....

The reason that's important is because the piston's downward "intake" stroke must be able to suck air into the cylinder through the intake port from the carb. The sucked-in air is then compressed as the piston rises on its compression stroke with both valves closed.

Holding the throttle wide open assures plenty of air to be sucked through the carb into the cylinder.

With throttle closed, the carb slide is down and blocking free flow of air through the carb bore.

Good Fortune!

Thank for the reply Lou. Where can I buy one of them non-screw type compression testers? Any recommendations on the model/type and a place to get 'em would be much appreciated.

I have the carbs off the engine now so I'm guessing open throttle is not a problem any longer. I just need to find some time and go fishing for a good compression gauge.

No eBay APP ID and/or Cert ID defined in Kunena configurationI think I've been using one of these for 25 years. I have a Sunpro, but I think Actron is the company that made them, or had them made.

I just placed an order for one from here. Thanks a ton!

No eBay APP ID and/or Cert ID defined in Kunena configuration

This the one I have now. Also very good.