XR 250R Engine Rebuild

Elijah — Mon, 03 Aug 2026 21:47:53 GMT

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	I tuned the low speed by adjusting the air screw to get peak RPM, and then counting the turns open. It's currently at 1.5 turns which I think is about right. Too much more or less than that is a sign you need to adjust the pilot jet.		I tuned the low speed by adjusting the air screw to get peak RPM, and then counting the turns open. It's currently at 1.5 turns which I think is about right. Too much more or less than that is a sign you need to adjust the pilot jet.

	After riding it on a rocky section, I found it was getting too much fuel again. There was some running out the overflow as well. I got a carb kit and replaced the fuel needle, and set the float level at 18mm (measured from carb body where the gasket goes, to the float arm). It would still overflow a little when I shook the bike side to side so I lowered it to 19-20mm. This seems to be working well now.		After riding it on a rocky section, I found it was getting too much fuel again. There was some running out the overflow as well. I got a carb kit and replaced the fuel needle, and set the float level at 18mm (measured from carb body where the gasket goes, to the float arm). It would still overflow a little when I shook the bike side to side so I lowered it to 19-20mm. This seems to be working well now.

			[https://www.vintagebikebuilder.com/setting-mikuni-float-levels.html Good info on measuring float level for these carbs]

	==Starting==		==Starting==
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	Then I watched a couple videos on the subject and I understand now what they're all getting at. You get it up on compression, but rather than trying to push through it, use the decompression lever to easily get past the compression stroke. Now you can give it a kick pretty easily. The lever is geared such that at the bottom of that kick, you'll push it over the next compression stroke but now with the engine's momentum helping you. The stock XR had an auto decompression tab which probably made kicking simpler. That has been removed on this bike and the manual decompression lever is the only thing in play.		Then I watched a couple videos on the subject and I understand now what they're all getting at. You get it up on compression, but rather than trying to push through it, use the decompression lever to easily get past the compression stroke. Now you can give it a kick pretty easily. The lever is geared such that at the bottom of that kick, you'll push it over the next compression stroke but now with the engine's momentum helping you. The stock XR had an auto decompression tab which probably made kicking simpler. That has been removed on this bike and the manual decompression lever is the only thing in play.

			==Lighting==
			The stock headlight is Ok but could definitely be brighter. A high and low beam would be great too.

			Stock tail light is a running light, it doesn't have an individual brake light. That's technically not street legal so I'm adding a brake circuit to the rear brake. The rear master cylinder uses an M10x1.25 banjo style connection which you can get aftermarket switches for. It triggers off the hydraulic pressure when you step on the brake. The tail light is a standard two filament bulb, and the holder even has the second filament wired up. So, I will just connect the brake switch across the existing running light and the unused 2nd filament to get a brake light function.

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XR 250R Engine Rebuild