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General Category >> Rubber Side Down! >> Decompression lever=Jake brake?
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Message started by Robawf on 08/08/16 at 21:47:45

Title: Decompression lever=Jake brake?
Post by Robawf on 08/08/16 at 21:47:45

Being I have a hand operated decompression lever, will it function similar to a Jake brake on large semi truck?
I.E. slowing the bike on a downhill grade, or will it cause adverse effects.

Title: Re: Decompression lever=Jake brake?
Post by verslagen1 on 08/08/16 at 21:57:34

No, it opens the exhaust valve killing any engine braking you have.

Title: Re: Decompression lever=Jake brake?
Post by batman on 08/08/16 at 21:59:31

not a good idea to even try!You could cause damage. Just close your throttle or for really steep hills down shift and close your throttle ,it will give you all the compression braking you'll need to maintain a constant speed.

Title: Re: Decompression lever=Jake brake?
Post by Kris01 on 08/09/16 at 16:35:56

With a closed throttle my bike slows down just fine all by itself. You shouldn't need anything more until you have to hit the brakes.

Title: Re: Decompression lever=Jake brake?
Post by Ruttly on 08/09/16 at 19:42:36

It's for starting purposes , not for slowing the engine , Period !
Not a Jake Brake not a diesel !
Yes it releases compression but it's not a 2 stroke !
For starting only !

Title: Re: Decompression lever=Jake brake?
Post by Dave on 08/10/16 at 05:30:19

The decompression lever moves a cam - which then prevents the rocker arm from following the cam profile all the way down, and as a result the valves are held off the seats slightly....which allows the compression stroke air to just go out the exhaust.

This system is designed for start up, and as long as the valve is help open the engine speed will not be any faster than the electric starter motor can spin the engine. The stock system only holds the decompression solenoid open for a very short period of time....maybe one or two engine revolutions. Using the manual decompression lever at engine operating speeds most likely would not be good for the cams and rockers......instead of the rocker following the cam profile as it normally does - the rocker would lose contact with the cam....then as the cam came back around it would "hit" or "slap" the rocker pretty hard.

And as others have stated - you would actually lose the compression braking, as the exhaust valves would be open slightly and air could move in/out of the exhaust pretty easily. Old hit/miss engines used this system to control engine speed - the exhaust valve was held open by a governor, and the engine could freewheel until the speed was slow enough that the governor released the exhaust valve.

Title: Re: Decompression lever=Jake brake?
Post by Serowbot on 08/10/16 at 07:13:39

That would be... un-jake braking... ;D
Let's call it coasting... :-?