headshot347

Member
Oct 14, 2006
103
0
Ya so i just got my CRF250R and i'm new to the four strokes. Been ridin 2 strokes all my life and now had to get me a four stroke bcus the track i ride at will only allow 4 strokes. now that i got one i don't know what the decompression lever is for. what does it do and why?
 

Jas_RM250

Member
Aug 7, 2006
16
0
Decompression lever releases a bit of compression for easier starting.

correct me if I'm wrong guys, but I'm sure I read that somewhere...never rode 4stroke (just 2stroke) but am a frequent mx mag reader...
 

mafols

Sponsoring Member
Nov 24, 2001
269
1
I think what you are referring to is a "Hot Start" lever. The decompression mechanism is centrifugal and is located inside the valve cover connected to the end of the cam....now you are probably more confused..... :coocoo:
 

RS1441

Member
Jun 18, 2006
54
0
I have the 06 crf250 and if you mean what i am thinking it is a hot start a little leaver above your clutch if you mean that then the name is pretty self explanatory if your not talking about that then i have no clue :P
 

mafols

Sponsoring Member
Nov 24, 2001
269
1
The decompression lever on an XR...for example is a lever on the handle bar that is pulled in to make starting the engine easier. The engine is stroked to top dead center with the kick lever. Pull in the lever, it opens an exhaust valve, and then gently push the kick lever a little to bring the engine just past top dead center, release the lever and kick. So basically you are opening a valve so you don't have to try and kick through the compression stroke...which in the case of an XR650R...really comes in handy. :)

On the CRF models the decompressor is "automatic" so to speak. At the end of the cam shaft is a little "thinga-ma-jig" that works like a manual lever. You'll see two half-moon shaped weigths with springs attached. When the cam is rotated slowly...as in the case of kick starting or E-starting with the X model....a little cam hits the exhaust valve rocker arm to open the valves during the compression stroke. When the engine fires up the centrifugal force of the cam shaft spinning fast overcomes the tension of the little springs and the mechanism is disengaged. :cool:

The "Hot Start" lever opens a little spring loaded plunger valve made into the carb. that allows cool ( ambient) air to be sucked in....making the engine easier to start when it is hot.

Hope that helps.... :cool:
 
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OldTimer

Member
Feb 3, 2005
475
0
Used to have a '93 Suzuki DR 650 w/decompression lever. Never could get her cranked when I used the lever. Now my right knee is shot from kickin' that beotch.
BTW - My 2-stroke '75 Suzuki TM 400 has a decompression lever as did many two strokes of the era. Guys used to use them when they slowed down to let the motor coast or something. Sounded like the "Jake brake" on a semi.
 

OldTimer

Member
Feb 3, 2005
475
0
Well... maybe :think:
Seems to me that it's there to relieve compression, but if you don't have compression then it won't start.
I obviously don't get it. That's why I hobble around like an old cowboy.
 
B

biglou

It's to pull only to inch the piston past TDC, then release it, kick, repeat until start. I know, I know, "where was I 13 years ago?" lol!
 

OldTimer

Member
Feb 3, 2005
475
0
biglou said:
It's to pull only to inch the piston past TDC, then release it, kick, repeat until start.
But you can ease it past TDC with a little steady pressure. You still have to kick through the compression stroke to crank the thing, no? :think:
I'm under the impression that the new fangled "auto decompression" is designed to lessen the compression during starting, no? :think:
 
B

biglou

I've only got my YZ426 experience to go by here. There was no way I could kick through the compression stroke on that bike in one swift kick. If I let my foot rest on it with steady pressure, it would bleed past the rings and it would rotate past TDC, but often very quickly, rotating to BDC. The key was to put it as little past TDC as possible, and it would fire. If you went too far, it wasn't worth kicking hard, just bring it around again and try to inch it past.

I can't explain how all the dynamics work here, but I just know I had a great "feel" for what was happening. Hence, I never had any trouble starting the beast. Well, there was that one time the spark plug was loose...
 

The Redrider

Member
Jun 14, 2019
238
32
Ya so i just got my CRF250R and i'm new to the four strokes. Been ridin 2 strokes all my life and now had to get me a four stroke bcus the track i ride at will only allow 4 strokes. now that i got one i don't know what the decompression lever is for. what does it do and why?
Ancient post. You purchased a four stroke because the track you rode at wont allow 2 strokes? I would say forget that dump, and go find another track....
 
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