2003 Crf450 weak Motor ?

[LABYZOUNE]

Hi, i hope someone here can help me.
I have a 03 crf450. I have tried newer stock bikes from friend (2006 YZF450, 2007 and 2009 CRF450 and 2008 and 2009 sxf450) and now i found that my 03 crf450 motor seems weak down low compare to the newer bike.
I have new piston and rings, a hot cam stage1, an fmf powercore silencer, new clutch, all valve are good.
All of these have help a littlle but my motor still not has strong.
I don't have any other 2003 crf450 here that i can compare to mine.
Any Idea ?
Thanks guy

 

[_JOE_]

Carb tuning.

 

[High Lord Gomer]

I put a higher compression piston in my 03 to help give it more low end. It also didn't hurt that Rich/Eric did a "little" tweaking to it, as well. :)

 

[LABYZOUNE]

The bike is jetted correctly. I have tried some jetting but it was better with the stock one.

 

[Matt90GT]

well you are about 5-10hp down on a new bike. The 05 year Honda really stepped up the motor game to over 50hp stock.

I would suggest to first look at your gearing. They did a change either 04 or 05 to the 13/48. I personally run the 14/52. Just makes it a different bike. Feels like you are on the pipe all the time. Everyone that rides my bike feels the same way. FYI this is the gearing windham has run for years outdoors.

second, step up to the newer 12.1:1 piston or better a 12.5:1 piston.

They address the jetting. There should be no noticeable bog or hesitation. You maybe 1 tooth off on the cam timing also. Just thinking of things. Your jetting for response will be all about the accelerator pump AP circuit.

Lastly, run a different exhaust. Nothing but good things about the MRD pipes.

 

[High Lord Gomer]

The gearing change they made in 04 was to go from 13/50 to 13/48. They did that because the 04 motor had so much more bottom that it could pull the taller gearing. If you did that to your 03 it would make it feel even worse. Going the way Matt did would help.

 

[LABYZOUNE]

Thanks guy for the help.
The piston is a stock honda from 2004 crf450.
It is suppose to have higher compression than the 2003 if i'm correct.
I'm pretty sure that the timming is ok because i have tried to go one tooth up on the cam but the bike becomes relly hard to kick...

 

[LABYZOUNE]

Anymore idea ? :-)

 

[whenfoxforks-ruled]

Did you alter/check the ap squirt? The wire up solid works, they sell aftermarket ap adjusters, changing the leak jet will help the engine come to life off bottom. JD is the man to hook you up with the desirable jets and maybe a new needle?

 

[Matt90GT]

I love how people just assume and guess at the timing of the motor. Really shows the duct tape mentality of wrenching on bikes that some have. Gosh it is not wonder the used 4 stroke market is riddled with horror stories!

CHECK THE CAM TIMING for gosh sake!

Pull the fill cap on the left side of the motor, line up the mark in the threads to the second hash mark. That is your TDC timing mark. Then look at the cam sprocket, the hash mark there should be EXactly on the arrow of the cam tower. PRETTY SIMPLE!

Next check your valve clearances and on the 02-06 cams the decompression clearance. Get a manual if you need help/specs.

After that, it is going to be about intake/carb/exhaust. What jets do you have in the carb? what setting on the needle clip? what settings for the fuel screw? What elevation. More than likely you will be modifying the AP circuit on the bike:

http://www.squadpage.com/pandora/Professor RedBeard450 How-To AP Mod.pdf

Do those mods with a #90 leak jet. that will modify up your AP circuit to working great for the bike.

 

[LABYZOUNE]

I love how people just assume and guess at the timing of the motor. Really shows the duct tape mentality of wrenching on bikes that some have. Gosh it is not wonder the used 4 stroke market is riddled with horror stories!

CHECK THE CAM TIMING for gosh sake!

Pull the fill cap on the left side of the motor, line up the mark in the threads to the second hash mark. That is your TDC timing mark. Then look at the cam sprocket, the hash mark there should be EXactly on the arrow of the cam tower. PRETTY SIMPLE!

Next check your valve clearances and on the 02-06 cams the decompression clearance. Get a manual if you need help/specs.

After that, it is going to be about intake/carb/exhaust. What jets do you have in the carb? what setting on the needle clip? what settings for the fuel screw? What elevation. More than likely you will be modifying the AP circuit on the bike:

http://www.squadpage.com/pandora/Professor RedBeard450 How-To AP Mod.pdf

Do those mods with a #90 leak jet. that will modify up your AP circuit to working great for the bike.

I have have check the timing , and the valve clearance, i think i was clear about that... But thanks alot for the AP mod link :-)

 

[LABYZOUNE]

Just an update about my problem:
I have install a powerbomb header (sx model) and it really wake up the motor. now i have very good bottom and midrange power. The have lost a little on top but it doesn't bother me .

 

[Rich Rohrich]

So you fixed the jetting by putting on a different pipe. I've always found that changing jets was a bit simpler and cheaper. ;)

 

[LABYZOUNE]

So you fixed the jetting by putting on a different pipe. I've always found that changing jets was a bit simpler and cheaper. ;)

hé hé hé ! no i have tried different jetting but it didn't help.
The pipe really help with the bottom end.

 

[Rich Rohrich]

hé hé hé ! no i have tried different jetting but it didn't help.
The pipe really help with the bottom end.

If you say so. ;)

Glad you found a solution.

 

[_JOE_]

Just an update about my problem:
I have install a powerbomb header (sx model) and it really wake up the motor. now i have very good bottom and midrange power. The have lost a little on top but it doesn't bother me .

Nah, it still needs jetted. He just shifted the problem area. :)

 

[_JOE_]

People comment more on those 1000+ dollar exhaust systems than they do on 4 dollar jets though..............

Even if the bike sputters and pops and won't rev out. :whoa:

 

[TRexRacing]

Man my '03 CRF never seemed down on power.Not stock,not with the Thunder Alley slip on and JD jet kit.Haven't found a hill yet I could climb from a dead stop.And I look.

 

[LABYZOUNE]

I don't say that it didnt had power , but compare to newer bike it was alittle "weak" down low.
I bought the complete system for 400$ can from 2nd-gear on ebay , brand new.
It's still more expensive than jet but hey since nobody here believe that i have tried a lot of jetting so...

 

[whenfoxforks-ruled]

I was unaware of any top end changes in the crf 450 ever, that made any drastic change to the power. Changed the exhaust flange angle a couple times, compression, decompression, crank center back/lower, made the valves smaller, and the ap adjuster, finally, just before efi? Most of their changes wrapped around the frame, or making the power hit slower/more usable? Most used ones, and some new ones, just need a properly performed engine rebuild and jetted. They ARE TOO fast for closed course competition.

 

[TRexRacing]

The '03 had a different cam than the '02.Biased for a booming bottom end-mid with a decent top end.There were complaints about the '02 being too rev happy.There's no such thing.Mine just rips from just off idle to way up there.I upped the compression to 12.5:1 and gained a bit.