Input needed!

[Cr250rider04]

hey guys. i just rebuilt my topend on my 04 cr250. I just got done taking it easy on it for break in. ( heat cycles.) I notice today when i started to rip on it wide open in the high rpms it kinda sound like a ping or tap or tick. kinda like marbles. what could cause this? coudl it just be the power valve? it runs great pulls strong just get a noise in the high rs. please let me know what you think. I wont be able to sleep with this on my mind

[VAL]

Is it when you have a load on it or even when you rev it in nuetral?
If under load only, it could be detonation.
Did you change to a higher compression arrangement. Piston work or modified gaskets?
Did you do anything with the stator or timing?
Did you have problems before you did the top end with the plug fouling and put in a hotter plug?

[Cr250rider04]

Originally Posted by VAL

Is it when you have a load on it or even when you rev it in nuetral?
If under load only, it could be detonation.
Did you change to a higher compression arrangement. Piston work or modified gaskets?
Did you do anything with the stator or timing?
Did you have problems before you did the top end with the plug fouling and put in a hotter plug?

Its only under load. when rebuilt i just used a wiseco prolite piston and cometic gasket kit. no mods done to the gaskets or head. I checked the plug and it was a light brown. Im running benol at 36:1 I broke it in at 32:1. its around 45 degrees out if it matters

---------- Post added at 03:54 PM ---------- Previous post was at 03:53 PM ----------

what can i do about it if it is detonation?

[VAL]

It could be something as simple as stale gas.
For starters, try running some fresh Premium gas through her.

[Cr250rider04]

I just put 93 in it from today.

[VAL]

Again, this is just from what you described.
Did you get the stock specification piston or the High performance package?
Had you done any jetting at any time prior to the top end job, leaning out the main?
Did you replace crank seals?
Is the sound rather loud or just like random rattling almost imperceptive sound.

[Cr250rider04]

Originally Posted by VAL

Again, this is just from what you described.
Did you get the stock specification piston or the High performance package?
Had you done any jetting at any time prior to the top end job, leaning out the main?
Did you replace crank seals?
Is the sound rather loud or just like random rattling almost imperceptive sound.

std piston kit. no high performance.
Hadnt touched the carb on it yet. noticed when i pulled the motor to rebuild it the plug was wet/black now its dry and light brownish.
no seals replaced.
Its just in 4th 5th gear at WOT. its not that loud but noticable

[2strkyz]

Have you ridden the bike in weather as cold as 45 degrees before, Maybe thats causing a lean condition... just an idea because if it were 45 degrees here i wouldn't know what to do.

[Cr250rider04]

havent owned it long enough. i tore it down 2 weeks after i bought it. it could be the weather.should i run it at 32:1 for colder temps? or adjust carb?

[2strkyz]

I would try adjusting the jetting or maybe moving the clip position on the needle, switching to 32:1 wouldn't really help as that actually leans the fuel air mixture because the extra oil displaces fuel.

[VAL]

Originally Posted by Cr250rider04

std piston kit. no high performance.
Hadnt touched the carb on it yet. noticed when i pulled the motor to rebuild it the plug was wet/black now its dry and light brownish.
no seals replaced.
Its just in 4th 5th gear at WOT. its not that loud but noticable

Colder temps will lean the bike out. Cold air is more dense that warm, therefore there is more air in the fuel air ratio.

That sounds like pre-ignition.

Going from 32:1 to 36:1 actually enriched you mixture but maybe not enough.
Check your spark plug too see if its the proper heat range.
If it is OK then try raising your needle one notch. ( that is actually putting the clip one notch down) ( I don't know how much experience you have so dont take offense to that overly explained statement)

Once you do that you may have to adjust you air and idle screw, don't worry though.


Let us know what happened.

[Cr250rider04]

its suppose to be 60s here this coming week. im gunna wait and try to ride it then and check things out. im almost positive it has the be the temps making it run lean. it was around 40-45 degrees when i was riding it.

[VAL]

Its all good.

These bikes are a little touchy on jetting. But they are fun as heck.

I forgot to say congrats on the top end job. I dont know if you have done this before but seeing as how it runs and you only have a little issue with pre-ignition, you did great!

[Cr250rider04]

thanks man! yeah Ive had many 4 strokes (06 crf250, 05 yz450, 08 yz450) and i went and bought the bike i always wanted the cr250 and its a blast to ride.I love to ride trails and track so it works perfect. This thing is so much fun to ride I never want to get off it. the 4 strokes i got bored. but yeah first top end job. wasnt hard at all. I wouldnt touch the bottom end tho. ill let a pro do that when it comes time. thanks for the info. well see how this week gos with the weather warming up. if it runs good then i know its jetting.