Compression starting.

15 replies to this topic
  • BrandonW

Posted October 16, 2002 - 07:32 AM


I have recently figured out how to compression start my bike, but before I go gung-ho with it, I'd like to know if it is something that I should avoid.

When I stall the bike, if I still have some momentum, or a downhill is near, I found that I can leave it in gear, pull in my decompression lever, and crack the throttle a skosh, and the bike wicks to life.

Searched, but did not see anything good or bad regarding this.

No problems or stay away?


  • mike_dean

Posted October 16, 2002 - 07:48 AM


I've done that several times with my 426 and no problems.

  • Dodger

Posted October 16, 2002 - 07:50 AM


I'm not a racer, so I'll usually take the time to do stop and do the drill.....................

With that said, damn near every time I "stall" my bike, it usually pushes my buttons in a way that I wack her back to life just as you's been discussed before. Some say you can hit your valves with the piston by participating in these types of activities, but as I remember the consensus was that there is no problem bump starting the beast.

How's that for a completely Non-Definitive answer :)..........


Dodger :D :D


Posted October 16, 2002 - 07:51 AM


You are not going to hurt it by bump starting it. We have been doing it for years without any problems....Now the closet mechanics will come out again and say...Oh no you'll bend a valve....BS

Roost on Bro....

Bonzai :)

  • cnacc

Posted October 16, 2002 - 10:48 AM


I started doing it at the local track so I wouldn't get run over, I have had no problems, so I keep doing it??? :)

  • x2smoker

Posted October 16, 2002 - 11:22 AM


On days I ride with my 11 year-old, I bump start about every mile. I just wait until I find a downhill and kill the engine and wait. Then when I see him coming, I can just roll down and keep on a goin'. I have found it necessary to shut off the engine instead of letting it idle because on hot days, the coolant will boil.

What I do is hold the comp release, shift into 2nd or 3rd, roll down, release the clutch, and very soon after, release the comp release. I've done it dozens of times and believe that it will not cause any ill effects to your engine.

In a couple of short years, my now 13 year old will be kicking my arse on the trails and then I'll need to teach him how to bump start his thumper after frequently waiting for me (if he lets me ride with him :)).

  • cnacc

Posted October 16, 2002 - 12:54 PM


x2smoker, just don't teach him all of your tricks all at once. That way you can keep the upper hand. That’s what my old man did, and it works pretty well. LOL :)

  • neWRiver

Posted October 16, 2002 - 01:58 PM


I started doing it at the local track so I wouldn't get run over, I have had no problems, so I keep doing it???

Either that or get run over. :D

Seriously, like x2smoker I do it all the time. If I'm going to stop along the trail I will try to do it where I can leave myself even a little bit of a down slope. Bumping is so much easier than kicking. Also, I do stall my bike from time to time and if the bike is still moving at all, a quick stab at the clutch and decomp lever always works for me. :)

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  • blue_beast_wins

Posted October 16, 2002 - 11:41 PM


YAMAKAZE, as a practicing mechanic rather than a try hard i agree, try welding a three inch bar (your lever) to a valve and see if you can bend it with one finger,maybe you can try wearing a superman costume.


Posted October 17, 2002 - 03:07 AM


Huh???? Did I miss something here??

Bonzai :)

  • AZWR426

Posted October 17, 2002 - 03:49 AM


What about the new 450? Will the new auto-decompression bikes compression start like a 2 smoke or do they have a compression release lever too? (Never thought I'd like a mechanical aspect of a two stroke again.)

  • Chaindrive

Posted October 17, 2002 - 07:13 AM


With e-start, who cares if it will bump-start?! :) I'm sure it will, my big-pig DR650 does.

  • bman

Posted October 17, 2002 - 12:56 PM


I have ridden the YZ 450. Yes it is very easy to bump start. I would think the WR will be the same or better. Or you just press the button. I am always using the compression release for bump starting. Nothing like locking up the rear wheel and kiling the motor on a narly rutted downhill. Pull that baby in that baby let the clutch out and like majic you are running and again in control. Not that I have ever been out of control.

  • blue_beast_wins

Posted October 17, 2002 - 06:46 PM


I think so, i did agree with you it isn't gunna hurt, does any body really think a plastick decomp lever with one finger applying pressure to it when you bump start your motor is enough to bend a valve when the piston touches it?? i think not. A camshaft in the wrong position however, well yes.


Posted October 18, 2002 - 02:39 AM


Ok... All the decomp lever does is causes the rocker to gently push down only on a corner of one of the Tappets breaking the seal by less than .002 alowing the trapped air/gases to escape while not interfering with the normal operation of the rocker arm. It doesn't push down like some have described so that the valve is exposed to the possibility of being smashed by the piston. The .002 space isn't even enough to make the valve break the plane of the upper surface of the valve seat.

I wasn't making remarks about your mechanical abilities, just that the "Shade Tree" mechanics out there seem to always come out with some far fetch sense of reality gained from some Drunk Front, BS session they attended at one time or another.

Bonzai :)

  • blue_beast_wins

Posted October 18, 2002 - 10:10 PM


i agree, no offence or any thing, some people hear or read something third or forth Hand and take it as gospel, no doubt going by some of your previous posts you know what you are talking about.


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