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?
Compression test on 99 xr400r
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They will work. The number will just be lower then normal.
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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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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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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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If your finger is long enough just stick it in the hole and kick. It should blow your finger off easily with the decomp disabled. It should still squeak air with the decomp properly adjusted. Make sure the decomp cable is adjusted correctly!!!!
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Yes, you need to lap the valve "seats" and "faces" . The seats are the rings pressed in to the head. The faces are the angled portion of the valve. It is important to make sure the lapped surface is within spec.......if it's too wide it significantly reduces the psi needed to perform. This requires special tools and knowledge.
Thank you! I lapped in new valves. I realized that one of the intake valves was slight bent and not closing fully. I lapped them in as best I could listening to the scoring. So far I can tell the difference in compression already without the cam in place and the spark plug hole closed. Before it still would turn at that point. I'm waiting on another plunger spring the other one had no spring to it. I hope as long as they open then seal back as good during operation it should improve.
Ok new valves lapped in, the feel of compression drastically increased. Without the decomp I can almost stand on the kickstarter, with it its easier. I tried the compression test again, it read 35 psi but I'm not sure if I did it correctly. After a spritz of starter fluid the bike crunk for a second. Couldn't get it to crank again! As difficult as it is to kick in finding it hard to believe the compression is that low?
What do you guys think? Any advice...
What do you guys think? Any advice...
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Well it's sounds like you repaired the compression problem. I will say that the plunger without the spring will give you very low compression so that was probably the main problem . Adjust the compression release correctly because it is very hard to start otherwise and you may break something. Now, you need spark that is properly timed and fresh fuel in a perfectly clean carb. It should start with all these components.
How do you adjust the pressure release? I tried pull starting it, it ran with me on the throttle a lil. It eventually died out after a min. I was sure to replace that plunger spring and timed it correctly! I'm baffled by the low compression reading especially since it crank
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