Crf 450 running bad in neutral on the stand

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#1
Crf 450 running like crap.....Please Help!!!

It all started when i got back from the sand dunes. It runs, but dies, missess, and stalls out passed half throttle. If i get on it quick, it dies. I took the carb apart thinking maybe some sand was lodged in there, but there was nothing. Then today i went out, started it, let it warm up, then when id give it some gas, if it didnt die it would miss, pop, and shoot flames out the tailpipe,also the headpipe glowed red, like it was about to melt. Like i said it just started happening right when i got back from the dunes, it always ran good up until now. What could it be??? timing?? tps?? running to rich???

Please help, i cant ride until its fixed!!!
 

Studboy

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#2
Check your valve clearances. Also, maybe you overheated or overreved the bike at the dunes???? I have seen a lot of guys seize their thumpers at the dunes here, but mostly 250Fs.
 
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#3
It's always difficult to tell by E-mail.., but when you tell it's running hot/"pops"/won't rev when gassed, Im almost sure it's running lean!
It takes an awful lot of gas to drown a 4stroke when you're idling, and then crack the trottle. Check accelerator pump/needle location/any leak by carb. mounting. Also make sure the HOT START slide is able to fall right back in closed position.
 
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#4
Sounds real lean. Check everything the previous guy said.
Last week I installed a flywheel weight. I started it up right after the install to go for quick spin around the neighborhood. It was running like crap, sounded weird, idling real low, sputtering, cracking, popping, stalling and such. I rode it for about 10 mins like this before I got worried. I thought maybe somehow I screwed something up installing the flywheel weight. Well after tinkering with it for about 5 mins, I realized I left the choke pulled out! I felt like a dumbazz, but I had a big grin on my face though when I realized it wasn't serious!
Anyhow, it might be something stupid like that, so check all hoses, filters, and such.
 
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#5
It sort of sounds like your accelerator pump ain't working. That's easy enough to verify if you can take the carb off, a stream of fuel should squirt out of a small brass nozzle at the bell towards the front when you lift the slide.

I do know that if I were to disable the accelerator pump on a perfectly running bike you would probably think all manner of things were going wrong, point being it does make a big difference. So I would check that first, if that is working I'd drain the fuel and replace with some fresh gas.

Hope this helps.
 

SFO

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#6
Hicks the man.
Hick, BTW, that piston kit you boosted me went to the eternal home of yz-f goodness RR.
I still owe you though...
Wanna check out the Dallas SM this weekend?
 
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#7
I did pull the carb off and the accelerator pump works fine! I dont think it is the jetting, because it ran perfert before.. I never touched anything, it just all of the sudden started happening. And it also has a new fresh tank of gas in it..
 
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#9
good call with the woodruff key, i did install a flywheel weight. i will check that out tonight!!!
 
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#10
Originally posted by SFO
Hick, BTW, that piston kit you boosted me went to the eternal home of yz-f goodness RR.
I still owe you though...
Wanna check out the Dallas SM this weekend?
I'm glad somebody got some use out of it SFO, I'd almost forgotten about that.


Thanks for the offer but I'm busy helping out with the family business all month, zero free time. I can't even go riding. At least I have my health. :-)


XR, if it isn't a fuel issue then it must be ignition. It almost sounds like the timing isn't advancing with higher rpms. Just more pure speculation, hope it is helpful.
 

Rich Rohrich

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#11
Originally posted by Hick

I'm glad somebody got some use out of it SFO, I'd almost forgotten about that.
Hick - I'll make sure it finds a good home in something sick and fun. :thumb:
 
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#12
Thanks for all your help guys, but i still cannot get this thing to run right. It just pisses me off. I have had this bike for about 2 months now, and up till now i have been very pleased with it. I have only got about 15 rides on it due to having to go to school during the week, and work on the weekends. I dont have very much time to ride, let alone work on my bike. That is why i bought a new bike. Now im back to the days of my xr284, i would ride on saturday, then work on her sunday. Now i know why honda doesent give out a warranty!!! I have never seen anything that was brand new brake down after two months of riding!! I probably will never buy another crf
 
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#14
completely went through the carb: jetting, accelerator pump, hot start, etc... Woodruff key, gas, spark plug,.

What else should i check? Valves?? tps?? ignition??
 

DougRoost

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#15
Valves. Have heard of CRFs eating valves with just a little dirt getting past the air filter. At least if it's a new one it shouldn't have the airbox sealing problems of the '02s, but any sand that may have gotten in there would wreak havoc.

Yet another reason I returned to the world of 2 strokes...