Suck, Bang, Blow?

Don't worry, we didn't forget about Squeeze. The KFX we've been working on did. KFX 400 If you remember last week, we found that the timing is right on and that the valves are within spec. But the bugger still won't start. And no, going out for ice cream then trying again when we get back doesn't work. We've tried it. Twice. So today we are moving on to a spark test and a compression test. While spark is normally the first thing you would check, this was a special case. Because it had started and ran for about ten minutes before it just stopped, we were concerned that the timing had jumped. And since we had the head off anyway, we figured it couldn't hurt to check the timing and the valve clearance. So if it seems like we're a little out of order, that's why. So to check the spark I got out my spark gap tester.  This tool is used to check the amount of power at the spark plug by measuring the length of the spark. It plugs into the spark plug wire boot (we talked about that on last week's Anatomy of an ATV about the ignition coil.) and clips on to the frame for ground. To check for spark, press the ignition button and watch for the spark to appear in the gap. A 20 mm spark is what the average spark on the KFX should be. We have more than 30 mm so we are good in that area. Spark Gap Tester Once we knew that we had plenty of spark, we were able to move on to test the compression. You will need a compression tester for this, as well as the right adapter to fit the spark plug hole. Compression Tester Set I have seen some homemade adaptors made out of an old spark plug but since most adaptors are available for $10 to $20, unless you absolutely have to have one right that second, it really doesn't seem worth it to make one. Luckily, I had the right adaptor. So I put the hose on the gauge and the adaptor on the hose. Assemble Compression Tester Then I carefully screwed the compression tester into the spark plug hole. Compression Tester in Head Now to run the test, I needed to make sure that engine was turning over fast enough. To do this I put some jumpers to another battery just to make sure. Jumper Cables So now I just cranked the engine over holding the throttle wide open. And you look for the needle to jump up to whatever the spec is from the user manual. As you can see, the gauge did not move at all so our compression was less than 25 psi. Compression Tester That’s not good. Now there are about three things that could cause the compression to be low. The valves could not be seating right but since these are brand new valves and seats, it's unlikely that is our problem. Or, the valves could be out of adjustment and the cam could be holding them open all the time; however, we checked the valve clearance last week and it was good. That leaves us with option number three, which is also most likely - the piston rings or cylinder wall is worn out. Well just what I wanted to have, another tear down post. But this is just one of the joys of ATV ownership. (I do love it)
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