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Decompression Lever Adjustment

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Howdy All:

I recently posted a few times about the difficulty in starting my 2002 XR400R.

While reading through the service manual, I noticed it said that an improperly adjusted decomp lever may cause similar problems. It said there should be 3/16 to 5/16 of free play.

Well, I went out and checked mine, and it was more like 1 to 2" of free play. You had to pull the lever almost all the way up until it felt like it was doing anything, and that was at TDC. To be honest, I don't think there's enough room on the adjuster to tighten it to the specs listed in the manual

Could that be the problem? Is the decomp lever adjustment that important? I'm assuming the answer to both is YES. But if any of you have any similar experience, I'd appreciate hearing about it.

Valves to be adjusted this weekend...just waiting on the motion pro tool.

Thanks again for all your advice and help.

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If the decompression lever has too little freeplay it can open the exhaust valve and you will lose compression. Too much freeplay won't hurt anything or make it difficult to start. I don't think the lever has much feel to it compared to a brake or clutch lever. To properly adjust it you should watch the arm that the cable is connected to on top of the cylinder head. You can also remove the valve adjustment cap so you can see exactly what it is doing. You should watch the arm move as you pull the lever, I would be surprised if the lever moves 1-2 inches with no movement of the arm. You should also make this adjustment only after the valve clearance has been properly set.

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Actually, it's best to make sure the decomp lever has the required play "before" checking/setting the right exhaust valve and adjust if necessary. Then check/set the valve clearance and then recheck decomp lever freeplay afterwards.

You should do it that way because of the reason you give of the valve possibly being held slightly open by no play in the manual decomp system.

Oxbow, you need to make sure you're TDC on the "compression stroke" when you check/set lever freeplay. If you have 1"-2" of pull on the lever with engine setup right and can't adjust it out, then you have something wrong with the mechanism at the head or the cable is not stock and must be too long.

If the decompression lever has too little freeplay it can open the exhaust valve and you will lose compression. You should also make this adjustment only after the valve clearance has been properly set.

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Actually, it's best to make sure the decomp lever has the required play "before" checking/setting the right exhaust valve and adjust if necessary. Then check/set the valve clearance and then recheck decomp lever freeplay afterwards.

That's right, if the decompression freeplay is too tight it can be a problem when setting the valves. I should have mentioned that. After I read your post I went and looked in my manual and what I saw was kind of funny to me. Under the valve clearance section it tells you to set the decompression freeplay first. When you go to the decompression section it tells you to always adjust the valves first. If you go strictly by the book Honda just gives you the run around. However if you understand how both systems work together you can figure out why it's important to adjust in the manner you described.

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