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Removing Decompression Assembly

X Project

X Project

Super Veteran
traxxas-modifier said:
im reposting here what bro haen posted in some topics:

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IF NOT REMOVED :
Advantage : easy to start whether using electric or kick start
the kick start wont 'bounce' back when u kick it

Disadvantage : because its working mechanism relies on engine rpm to throw it out of contact with the pin on the cam, sometimes when the rpm hits 1500-2000 its activated and makes ur engine lose compression, try this at gear 3 to gear 4 change, because the gear 4 ratio is soooo different, the rpm drops suddenly and makes this mechanism active and u get loss in performance.

IF REMOVED :
Advantage : no more compression loss of course
no 'sudden performance drop'

Disadvantage : depends on ur cam profile, it need a stronger force to kick start ur engine, if the cam lift is very high (higher compression), you might need stronger battery to start the engine using electric starter.

IN GENERAL,
decompression assy is just a feature with its plus and minus side, so it wont hurt ur engine if you remove it or not remove it.
It's your choice, do u want max performance, or ease of start ?

technically, decomp assy should be activated only on rpm under 1500.. but u know.. sometimes something happen...

yes, thats why gear 4 dropped soooo much....

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Click to expand...
Actually, the lift or profile/specification of the cam has nothing to do w/ the compression issue of the engine... Maybe you had this the other way around bro... The higher the lift, the lighter and easier it is to crank the engine, especially if it has big valves, trust me... That's why the compression ratio as well as the quench is being altered or piston is moved closer to the head... The reason why it's hard for the cam to complete a full cycle ATDC is because, mechanically, the Valve Spring became much stiffer and sometimes leads to coil bind if cam has a real high lift and has not been taken into consideration and this refers to mechanical issue not w/ compression... And the simplest answer regarding the disadvantage is a no brainer at all, the decompression assy is removed so the compression is high, as simple as that... Tnx
 
JamesCore

JamesCore

Super Veteran
regarding to the electric starter, we have to use higher kind of battery. what models of battery we can use if we took off the decompression assembly?...
 
H

haen

Super Veteran
@X-Project : exactly what i mean.. higher lift causes more air fuel to enter combustion chamber.. more potential energy to burn.. CMIIW.. thanks for saying that in understandable way.. LoL..
 
JamesCore

JamesCore

Super Veteran
X Project said:
[quote="X Project":3qzpxax7]Go for the usual brands w/ 9amps 12v
Click to expand...
Stock is 5amps 12v[/quote:3qzpxax7]

thanks x project. what if my engine is still stock and i removed the decompression assembly do i have to change my battery?
 
john-locke

john-locke

Veteran
i have a kit 180cc malossi and it is very hard for the electric starter . many poeples burn the electric starter with this malossi . For me impossible to remove this decompression . i kill it .
 
S

syfull

New Member
im using yypang racing cam now,it doesnt use the decompression assy now..and this sometimes cause my bike to "kick back" my leg when i try to start it..is this ok?
 
depedal

depedal

Super Veteran
will the removed decomp lever/assembly still work if used with stock cam? i need to replace my rcam with stock cam for a while. if used with stock cam, is the performance with regards to power/torque is lower/poor compared to when the decomp assembly is still intact?


tia
 
athlon

athlon

New Member
depedal said:
will the removed decomp lever/assembly still work if used with stock cam? i need to replace my rcam with stock cam for a while. if used with stock cam, is the performance with regards to power/torque is lower/poor compared to when the decomp assembly is still intact?


tia

it is can up the performance if we remove the decomp in stock camshaft???
Click to expand...
 
EinVer

EinVer

Super Veteran
we just removed the decomp assy pin this afternoon on my T135
i liked how it performs now, better response on low rev
and no sudden power loss

but after a few testing, a problem arises. the decomp assy is ticking
and its very irritating
ill have to bring it back to my mechanic tomorrow

@ traxxas - do we have to remove the cylinder head just to remove the remaining decomp assy?
i can't seem to find the page on the service manual where it says about decompression assembly.
 
6sic6

6sic6

Super Veteran
sir einver, you need also to remove the moving part..... so there will be no ticking some anymore..... you can use grinder to remove it....
 
EinVer

EinVer

Super Veteran
6sic6 said:
sir einver, you need also to remove the moving part..... so there will be no ticking some anymore..... you can use grinder to remove it....
Click to expand...
is there any other option than using a grinder?
i dont think yamaha service shops have those kind of tools
and i like the idea that i can still change it back to stock form... just in case... :)

the way i see it, we need to remove the cylinder head to remove the sprocket together with the decomp assy,
but then again, im not that familiar mechanical parts
so i really woudln't know
 
6sic6

6sic6

Super Veteran
you don't need to remove the head sir just unscrew the sprocket at the side.... you can't remove the moving part unless you use grinder because it was fixed like rivet....
 
EinVer

EinVer

Super Veteran
thanks for clarifying that 6sic6

i guess we'll just return the decomp assy pin as i really didn't see any grinding tool there
(unless it was hidden hehe)
i'll leave it until my next tune up.

for those who are curious, removing the decomp assy really did help with the performance on low rpm
no hiccups or sudden power loss, even if you run with just 1500 to 2000 rpm
(i have a tacho, that's why i can tell)

downside are:
- electric start obviously have a hard time making a first turn on the engine
but i think it can be fixed with a bigger capacity battery, or installing some capacitors to help on the battery
- kick start kicks you back, for me its tolerable since i once used a motorcycle with the same behaviour on the kick start
but for those who got used to the soft, easy kick start... you wouldn't like it

btw, my ride has an all stock engine / mechanical parts
 
Abbie S Hir

Abbie S Hir

New Member
hey paps out there..im a newbie here and new in using a sniper...i have just observed that the engine of my r edition that i just bought last month have an annoying sound on the engine..is that common or not?thanks...abbie from ilocos..
 
boldstardex

boldstardex

Moderator
Staff member
Abbie S Hir said:
hey paps out there..im a newbie here and new in using a sniper...i have just observed that the engine of my r edition that i just bought last month have an annoying sound on the engine..is that common or not?thanks...abbie from ilocos..
Click to expand...
have it checked to your mechanic sir
 
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