Pulling in the decompression lever


11 replies to this topic
  • Todd98YZ400F

Posted December 07, 2004 - 07:21 PM

#1

I seem to have no problem pulling the decompression lever in then releasing it half way thru the kick to start my bike. Is that the right way to start it? Thanks.

  • Hick

Posted December 07, 2004 - 10:17 PM

#2

I seem to have no problem pulling the decompression lever in then releasing it half way thru the kick to start my bike. Is that the right way to start it? Thanks.



I would say no, but if it works for you what the heck. It may be possible to just miss TDC this way and perhaps hurt your knee or leg...

Most, like me, would say that the decomp is only pulled to nudge the kickstart lever just past that really hard spot, then you let go of the decomp, let the lever reset, and kick it from the top all the way through.


But I ain't arguing w/ what works for you. :cry:

  • Todd98YZ400F

Posted December 08, 2004 - 12:07 AM

#3

Yeah, you're right with starting at TDC as Yamaha even states on how to kick these bikes over. I think it's a safety reason as well as it can really jar your leg if you don't use (or forget to pull) the decompression lever? I'm not sure? It's all a timing issue and it's not that difficult once you get the hang of it. You're basically doing the same thing as auto decompression on the newer bikes, you're just involved now. I would really call this something like "semi-auto decompression starting". The decompression lever gives you auto decompression by you pulling it. Then you have to release it at about mid kick which is the manual, timing part by you. The momentum of your downward force starts the piston moving at a good enough pace to usually turn it over no matter where it's at in the cylinder. Especially when the engine is warm. These Yamaha engines are so well engineered they seem to start no matter where the piston is at. Unless you catch the piston at or just about at the bottom. Then you just pull the decompression lever all the way in and kick it thru to bring the piston up or to TDC itself then use the same method over again. I can actually sit on the seat of the bike without raising my butt up to kick it over with this method. You should try it and see how it works for you? It's so much easier and faster than going to TDC first, especially when the bike is cold and needs more than 1-2 kicks. Oh yeah, always wear your MC boot when kick starting a big bike like this, it's much easier. Even though I've been out in my garage starting my bike with my tennis shoes on with this method. :cry:

  • grayracer513

Posted December 08, 2004 - 07:22 PM

#4

The idea is to use the compression release to get you past TDC and part way down the power stroke. then release the lever, reset the kickstarter back to the top and give it a full kick all the way through. This give you a full turn and a half of the crank to build up speed and make it easier to get through the next compression stroke. Speed at the beginning of the kick does nothing; speed at the end gets it lit. So pushing the crank through smoothly, building speed as you go usually works better.

  • thumpinscott

Posted December 08, 2004 - 10:05 PM

#5

That's how I always did it before I did the cam swap. Pull it in and let it out as I was kicking, usually sitting. I tried the TDC thing but it never worked well for me. I never wound it up, I just kicked it using the same method. Now it's all better.

  • Todd98YZ400F

Posted December 08, 2004 - 10:43 PM

#6

I really want to do the cam swap so I don't have to teach my friends how to start it. I mainly got this bike so I could ride with my bike/quad-less friends. I have a Raptor 660 along with the YZ400F now.

It actually starts pretty easy doing the manual decompression once you get the hang of it. Bringing the piston to TDC is a hassle and kind of annoying if you keep missing it when trying to click it lightly. Pulling the decompression lever in and releasing it at mid kick is the easiest way to start these bikes.

Scott,

Was it a easy DIY job on the cam swap? How long does it take? I think I'm going to do that soon....

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  • Todd98YZ400F

Posted December 08, 2004 - 10:48 PM

#7

The idea is to use the compression release to get you past TDC and part way down the power stroke. then release the lever, reset the kickstarter back to the top and give it a full kick all the way through. This give you a full turn and a half of the crank to build up speed and make it easier to get through the next compression stroke. Speed at the beginning of the kick does nothing; speed at the end gets it lit. So pushing the crank through smoothly, building speed as you go usually works better.


I find these bikes start up with less than a full stroke (from TDC) even when cold. You can try this method after your bike warms up and maybe you'll see an advantage? After the bike warms up, I think you could have the piston travel 25% of TDC (starting 3/4s the way down) and it'll still start on the first kick with this method. I can't believe this decompression lever is only for making it easier to get to TDC. I don't even need or want the lever pulled in when I use the TDC method of starting because it seems I always miss it.

  • grayracer513

Posted December 09, 2004 - 02:07 PM

#8

My experience with decompression levers on big 4-stroke singles goes back to the days when they weighed 320+ pounds and had less than 4 inches of suspension at both ends. The way I described is how it was always done. I have noticed that a lot of 426's seem to have a favorite point to start from, but other than that, they aren't any different except for the vastly lighter crank assemblies used now. The lack of flywheel effect makes running through a complete compression stroke much more difficult than it used to be.

  • stainlessTT

Posted December 09, 2004 - 06:39 PM

#9

I have a 04' YZ450F and I NEVER use the decompression lever. It usally starts on the second or thrid kick.

Is it better for the engine or something?

  • spy

Posted December 09, 2004 - 06:45 PM

#10

Well you have auto-decompression. The 400s and 426s dont.

  • Butta

Posted December 09, 2004 - 07:37 PM

#11

I have a 04' YZ450F and I NEVER use the decompression lever. It usally starts on the second or thrid kick.

Is it better for the engine or something?


That's interesting....I've got a '98 YZ and a '98 WR and I NEVER use the electric start, either.....

:cry: :cry:

  • thumpinscott

Posted December 09, 2004 - 08:56 PM

#12

The cam swap is real easy if you are a little mechanically inclined.





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