Friesen

Member
Jun 27, 2007
12
0
I've been riding 2 strokes for 15 years and looking to make the switch to the 4 stroke.
Currently I'm looking at a 2005 or newer CRF450R. But, I'm concerned about the throttle response of the 4 stroke. You know... the 'bog'!
My 2 stroke throttle response is immediate! So there's my concern

Questions:
do all 4 strokes have this?
Does anyone know if the 2005 or 2006 CRF450 has this 'dreaded bog' issue?

Finally, is it fixable? if so, what mods are needed to get that 'snap' we all are looking for.

Thanks for your responses!
 

May 10, 2007
957
0
my bike has no bog. just warm it up or down shift. it will bog it it isnt warmed up though so make sure its nice and toasty. it doesnt help if starting in 3rd gear either though

if it still bogs get the carb rejetted
 

NM_KDX200

Member
Dec 29, 2002
441
0
My '04 YZ450F doesn't bog but then it was setup by my dealer who knows what he's doing (I ride with him almost every week). Where does the bog occur and when? On my bike, turn the throttle- it goes. My old KDX200 and KX bogged more.
 
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_JOE_

~SPONSOR~
May 10, 2007
4,697
3
My 06 crf 250 is supposed to be the king of bog. A JD jet kit, AP mod and timing set properly, and some pilot jetting work and the thing is instantly responsive. Some places such as Tokyo Mods will do it all for you. Go for it, the linear power delivery is great.
 

Friesen

Member
Jun 27, 2007
12
0
Thanks for the replies. Sounds like proper jetting and a boyseen AP is the answer to reduce the bog.

Has anyone had good results with the Power Now and Power Now Plus carb inserts?
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
Fine tune the ap circuit=no bog. Anything to make the ap circuit hold more or pump more,bad. JD's needles and secret o-ring on the ap adjuster excellent,diaphragm mod is questionable. My experience with the crf 450 has showed me the most powerful off road bike I have ever ridden,way to fast for closed course competition,but to each his own. And the crf,as usual for honda,the best built! Bog worse than a 2t,only when it had issues!
 

_JOE_

~SPONSOR~
May 10, 2007
4,697
3
Yeah, some FCR carbs have really rich accelerator pump circuits. Mine had a 50 leak jet. The leak jet controls how much fuel is allowed to return to the float bowl. I have tried a 70 and 90 so far. I seem to like the 70 best. No bog, but a smooth transition from bottom to mid. I also shaved the rivet on the diaphram. I use the fat o-ring from my JD kit. I have been impressed with the low to mid, but am going to try dropping the main a size in hope of some more revs. :ride: :cool:
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
Any fcr carb,yes they all have the same issues,07 and newer may be different!Get the jetting,timing and valves in spec and it is an indestructible machine(except for the snapped rods thing). Response is best felt with quality fuel,mtbe based fuels deliver! The 70 is what I settled on for a mid temp baseline,I believe the pilot went a couple smaller and the main one,needle 2nd from top.The popping and bogging gone,that bike can get up,unbelievable! The diaphragm mod,I do not know exactly where its going,increase the ap squirt and to what extent,the burst of raw fuel just clears the slide,its to help the off idle transition,not dump a half a bowl of raw fuel in and out to burn in the header!The ap adjuster,if you watch it,it floats,hesitates and sometimes does not squirt. The o ring mod takes care of that,if you wire it solid the arm bottoms out,that is where I thought grinding the diaphragm came from,but the o ring lets it stretch. Jd's multi taper needles seem the next ticket!
 

Ol'89r

LIFETIME SPONSOR
Jan 27, 2000
6,961
45
Friesen said:
So any bog can be fixed with say... JD jetting kit for proper jetting, even with the stock AP?

The stock AP works fine if it is adjusted properly. Many people adjust this to squirt too much fuel into the engine too soon. This floods the engine and causes a bog. Adjust the AP so that the slide opens a little bit before the AP squirts fuel. Most of the jets in your carb don't actually start to work until the slide opens a little.

Same problem with many of the aftermarket AP's. More is not always better.

Just my $ .02
 

_JOE_

~SPONSOR~
May 10, 2007
4,697
3
As I understand it, the rivet shaving must be done if wiring the arm, and increases the duration of the squirt. With a larger leak jet you shoot a leaner charge. In essence you are using the same amount of fuel over a longer duration. Mine runs really strong and the response and torque down low is imressive. As ol 89er said, the timing is also crutial.
 

Friesen

Member
Jun 27, 2007
12
0
I'm the poster of this question: Update.
I bought a 2006 CRF450R and have a FMF Q2 pipe on it.
the original owner left the jetting stock with the exception of turning the fuel screw out 1/2 turn.

No Bog and throttle response it dead on.
I'm very impressed! and pleased.

Thanks all!!
 

Spokes574

Member
Apr 27, 2001
171
0
I have a Y05 CRF450R.
I never had a bog issue on this bike.
But to improve throttle response two things helped.
Must adjust your Air Screw everytime there is a major
temperature or humidity change and
if you add a Boyesen accelerater carb cover that
improved throttle response on my bike also.

Also, replacing the carberator o-ring gaskets is a good
idea if the bike has a lot of hours. The o-rings are
cheap ~$15 max to do the entire carborator.

I also have the power now and the power plus.
To tell you the truth, it did not do much.
It feels like it has a tab bit more pull, but nothing significant.
If I could do it over, I would not have spent the $180.
A CAM or high compression piston is money much better spent than
the power now devices. I also eventually had done do I know
the impact of these mods.

Spokes574
Pleasanton, CA
 

RiDiNGCRF

Member
Jul 16, 2007
16
0
I ride mainly desert with my bike, so I just re-jetted her properly and there is never a bog, unless she's been sitting in the garage too long. But once she's warm, she's good to go. None the less, I think the throttle response of the thumper will actually surprise you.
- Heather
 

RiDiNGCRF

Member
Jul 16, 2007
16
0
Friesen said:
I'm the poster of this question: Update.
I bought a 2006 CRF450R and have a FMF Q2 pipe on it.
the original owner left the jetting stock with the exception of turning the fuel screw out 1/2 turn.

No Bog and throttle response it dead on.
I'm very impressed! and pleased.

Thanks all!!

Opps! I didn't read that far along! I'm glad you like the bike!
- Heather
 

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