Compression test on 99 xr400r - Honda ATV Forum
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post #1 of 19 (permalink) Old 07-09-2019, 06:16 AM Thread Starter
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Compression test on 99 xr400r

I recently had a new piston, sleeve, and gaskets replaced on my xr400r with the decomp lever. I used my compression tester on it and its not showing a reading! I was told at home compression testers won't work with the decomp lever. Is this true?
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post #2 of 19 (permalink) Old 07-09-2019, 09:39 AM
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They will work. The number will just be lower then normal.

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post #3 of 19 (permalink) Old 07-09-2019, 01:44 PM Thread Starter
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Thanks! Mine isn't reading anything and I'm confident the rings, piston and sleeve are in correctly.
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post #4 of 19 (permalink) Old 07-09-2019, 03:09 PM
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Valves adjusted right? If they are to tight you wont get any compression. Also could be a blown headgasket.
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post #5 of 19 (permalink) Old 07-09-2019, 03:13 PM
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A friend of mine had the same problem years ago with the same bike. He forgot to install the spring loaded plunger for the decompression mechanism. Once installed it fired right up.
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post #6 of 19 (permalink) Old 07-09-2019, 04:33 PM Thread Starter
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I have the intake set at .1 and exhaust at .12... All gaskets were replaced. How will I know if they're too tight. I made sure the .1 gauge slid in and the .12 couldn't in the intake to make sure they weren't too loose
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post #7 of 19 (permalink) Old 07-09-2019, 04:35 PM Thread Starter
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I made sure that plunger and spring were in there. The plunger didn't have as much spring back like the one in my trx400 but it was there and appeared ok
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post #8 of 19 (permalink) Old 07-09-2019, 06:31 PM
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I look for a steady drag when adjusting the valves. You want to make sure you can fit the feeler gauge back in but tightly with good drag the whole slide out. Sounds like you got them right for sure. Or atleast not to tight. Did you get the head decked? They warp easily. Which could result in an instantly blown headgasket.

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post #9 of 19 (permalink) Old 07-10-2019, 01:08 AM Thread Starter
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No I didn't. Is that having them shaved? I just don't see why it's showing no compression at all on the gauge but I can feel air pressure from the exhaust pipe. Could oil level effect the compression?
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post #10 of 19 (permalink) Old 07-10-2019, 03:35 AM
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Maybe your compression tester is not sealing in the spark plug hole? Or maybe your gauge died? Or maybe the schrader valve in the end of the fitting is stuck open?
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