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Crawling68

Decomp Lever?

23 posts in this topic

Forgive my lack of knowledge, but where is the decompression lever supposed to be mounted. Is it forward to be used with the index finger, or back to be used with the thumb, or is it just preference?

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The OEM installation mounts it with the clamp inboard of the clutch perch, above the clutch lever , facing forward. That way, it's easier to use both levers together, like when starting in gear, bump starting, etc.

Facing it rearward, or downward for use with your thumb introduces the risk of sticking yourself with it.

The best place of all to mount it is in the trash. Install the exhaust cam from a YZ450 and ditch the whole manual system. :thumbsup:

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I had a trusted local shop put a 03 cam in the wifes 250f and it made a world of difference.It now starts easier and it's nice not having to do the decomprssion ritual you have to go through to get the bike started. Well worth the $160.00 for the cam and install. :thumbsup:

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That sounds good, but whats the difference?

You will be able to just kick start it like a 2stroke. No finding TDC, pulling the decopression lever and kick a little further, let off the lever and kick.

Basically I believe the new cam holds the exhaust valves open for a tad longer so you won't need the decopression lever.

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The grinds are very similar in and of themselves. In a YZ426, the power curve becomes longer and flatter, without the sudden surge in the lower mid range; just a hard steady pull. In a WR, as far as I know, the effect is some what the same compared to a WR426 cam, but the timing is different between the two.

The way the auto decompression works is that at speeds below idle, a flyweight is retracted by a spring, which, by rotating a shaft in the center of the cam, extends a pin that sticks out next to the left exhaust cam lobe. This pin is positioned so that as the engine starts to come up on the compression stroke, the pin pushes down on the left exhaust valve lifter and moves it off the seat, relieving compression pressure. At about 60 degrees before TDC, the pin rotates off the lifter, the valve closes, and the engine develops enough compression to start (about 110 pounds, instead of nearly 200). So in truth, the device is a compression reducer, not a release.

Once the engine starts, the flyweight overcomes the spring, retracts the pin, and the unit ceases to have any effect on things.

It's important before you make the swap that you decide on whether to go with a WR450 cam, or the more aggressive YZ timing, because the fact that the decompression pin needs to be correctly timed prevents simply re-timing the cams between the two specs.

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I am new to my WR450 and am trying to laern as much as possible. What is this decompression lever you guys speak of and what is this starting ritual? I only push the on/off button, Hold in Clutch and Kick. Also does the bike need to be in gear to start?? I'm kind new to the manual cluth ordeal.

Would this lack of knowledge explain why last night trying to start, the kickstarter just stayed down and didn't return adn will not NOT return on it's own?

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The kick start should definitely come back on its own!!

As far as the decompression lever, As far as I know, the lever they are talking about is for hot starts only. After riding for a little while it helps to pull the hot start lever then kick start it.

I too thought it was a decompression lever. Maybe I am a little confused and they are considered the same thing. :ride:

I also learned that on a cold start, there was always an "old Yamaha Trick"

which is to give two shots of the gas before attempting to start the bike. Then kick it over.

I tried this and wallah!!. The new WR started right up . Before I was trying to kick or electric start the thing and it was taking it good old time. Not any more.

Give it a try. You'll be amazed at the results

Lit_dueler :thumbsup:

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I am new to my WR450 and am trying to laern as much as possible. What is this decompression lever you guys speak of and what is this starting ritual? I only push the on/off button, Hold in Clutch and Kick. Also does the bike need to be in gear to start?? I'm kind new to the manual cluth ordeal.

Would this lack of knowledge explain why last night trying to start, the kickstarter just stayed down and didn't return adn will not NOT return on it's own?

The WR450 doesn't have/need a decomp lever as per the explanation grayracer513 made above. Your kickstart problems have nothing to do with the decomp lever.

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There is no decomp lever on a WR450

98-02 400's and 426's had them on the left bar, and you need them to start hence the "starting routine"

03- on have a different exhaust Camshaft that allows you to start the bike without the manual decomp

the HS on older models 98 and 99 for sure, not sure about newer, had the HS button (air valve) mounted on the carb. Later they moved the HS to the bar and used a lever.

USE the HS when you stall or crash a hot bike. It allows air into the carb and makes RE-starting easier.

if your kickstart does not return, you probably have a broken spring.

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how do you "Give it 2 shots of gas".

I think the return spring on teh kickstart just failed.

When the bike is NOT running, simply rotate the throttle 2X quickly. The idea behind this is that, after the bike haas been sitting, there usually is no gas in the carb. By giving it a couple quick shots before attempoting to start the bike, it put gas directly into the carb. Which aids in starting.

I know that with my WR, I was a little suprised at how long it took to start, without giving it gas. The guy I bought it from told me not to give it any gas.

However, he was right on one thing, DON'T give it gas at the same time your trying to start the bike. This WILL flood it!!!

Give it a try and let me know what you think

Lit_dueler :thumbsup:

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So changing out the cam is best left to a shop i assume. Is there anything else involved, or is it just swapping out the cam.

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The decompression lever on the wr 400 is to open one of the exhaust valves, there fore releasing compresion in the cylinder to allow the piston to pass top dead center for starting. The engine has very high compression and simply kicking the bike like a 2smoke is not possible unless the 450 cam is added. The decompression lever doesn't have anything to do with hotstart, there is a seperate unit for hot starts located on the left side of the bike mounted to the frame by the choke. Now bear in mind I am speaking of my 98 wr 400 I do not know about the new 450.

PS your kickstarter should return on it's own!!!!!

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So i can just put the WR450 cam in and leave the WR timing right?

You got it! :thumbsup:

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So get the WR450 cam, install it in the same exact way as the one i have now, make sure the valves are shimmed in spec and call it good huh, i think i can do it. Does anybody have the part number for the 450 cam.

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So get the WR450 cam, install it in the same exact way as the one i have now, make sure the valves are shimmed in spec and call it good huh, i think i can do it. Does anybody have the part number for the 450 cam.

The part number is on the instructions :thumbsup: Just make sure to install it with the same number of links between the dots on the cams as the picture shows.

http://s18.photobucket.com/albums/b122/byggd/?action=view&current=450cam_Page_1.jpg&refPage=20&imgAnch=imgAnch22

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