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So i was riding my 01 yz250 on saturday for the first time. Went really well for about 4 hours and then all of a sudden the engine just switched itself off- no funny noises, or clunks or bangs- so I went to kick it back in to life and it now has no compression. It has a tiny bit but i can push the kickstarter down by hand quite easily. It had a rebuild in may this year with a wiseco piston and has been well looked after and only ridden once a week for a few hours. Any ideas- my mechanic friend thinks it is the rings, but i thought it was weird that it went from full compression to nothing, just like that. Any help would be much appreciated.

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That is a great site Dt posted.

Also, check your timing using the timing thread.

Melted pistons are generally from detonation, and timing (along with mixture) is a major detonation factor.

BR8 heat range plug and back flush your radiators and clean all water jackets.

Timing Thread

What is your altitude, temperature and main jet size?

Fuel being run?

Also could have been a leaking base or head gasket, intake or left side crank seal

causing a lean mixture resulting in detonation.

Generally for a 2T piston to melt that badly, it had to be on the main jet circuit at high power output (which is harder to hear too)

Did you hear detonation? A rattling-pinging noise as you applied throttle or ran up into a rev range?

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Could be.

Detonation sounds like a rattle/tick at low speed and more of a tickticktick at higher speeds.

At lower speeds and small power settings, it generally doesn't show an effect on the piston/head.

Damage really starts to show up from the midrange up or once you're on the pipe and it starts detonating.

A little brief tick or rattle off the bottom on throttle crack generally isn't a problem.

At what point are you hearing it, throttle setting and RPM?

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The initial throttle crack is no big deal.

Often, you can solve that by just turning the A/S in 1/4-1/2 turn.

The ring at high RPM is more concerning.

That is at full throttle right?

Is it like a steady tone or ticking?

One way to check that sound is to just run a gallon of race gas and see if it goes away.

Race gas will kill that immediately if it's detonation and only occasional.

If it doesn't go away, it's prob. just a ring/piston/cylinder vibration that all 2T's do sometimes.

That's most likely it, but I'd still run the gallon of race gas to check to be sure.

If the race gas does fix it, you can do one of three things.

-run the race gas

-retard the timing

-bump up the main jet to the next richer size.

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Occasionally, when riding I hear a metallic sounding noise, I always pull my engine apart and see nothing and the clearances seem fine, is that detonation/pinging that Im hearing?
The initial throttle crack is no big deal.

Often, you can solve that by just turning the A/S in 1/4-1/2 turn.

The ring at high RPM is more concerning.

That is at full throttle right?

Is it like a steady tone or ticking?

One way to check that sound is to just run a gallon of race gas and see if it goes away.

Race gas will kill that immediately if it's detonation and only occasional.

If it doesn't go away, it's prob. just a ring/piston/cylinder vibration that all 2T's do sometimes.

That's most likely it, but I'd still run the gallon of race gas to check to be sure.

If the race gas does fix it, you can do one of three things.

-run the race gas

-retard the timing

-bump up the main jet to the next richer size.

+1, have same question for carver...

kindly see vids and comment whether my bike is pinging (or is the pipe just creating some resonating ticking sound)... obviously i don't hear it as a rider.

http://www.livevideo.com/video/051AF817718F4504B3A93B46DD34790D/dirt-bike-trail.aspx

2nd gear cruising

same hill at 3rd gear (perhaps near WOT, driven by my friend "wildman" who owns a 525EXC)

don't forget to turn-on your speakers... and close your eyes haha! 👍

background: jetted at 45 pilot, 172 main, N3EW 2nd clip, 96-octane pump gasoline premix at 40 : 1 motul 800 2T, prevailing temperature around 80ºF, no access to race gas

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I think you're fine.

Maybe a just a touch of occasional tick each time the bike bogged down on the first vid but not really noticeable,

and that's normal imho when the engine momentarily bogs at low RPM with the throttle open.

You could see if that goes away by turning the A/S in 1/4-1/2 turn, but it sounded minor.

99% of that is just 2T pipe sound, but I thought I heard a touch or tick of minor ping.

In the second video you hear the 2T "ring" near the top of the hill.

I think that is the standard ring/piston/cylinder vibration that 2T's do

and every 2T I've ever had has had some "ring" at some RPM which

is just a characteristic of your rings/piston/cylinder clearance and vibration.

BB, listen to the second video and see if your "ring" is liike that.

Sounds like a normal 2T to me.

Anyone who ever has a question though can do the gallon of 100+ octane though and answer it quickly.

Just remember your engine has to be at the same temperature/load/outside air temperature to compare.

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The initial throttle crack is no big deal.

Often, you can solve that by just turning the A/S in 1/4-1/2 turn.

The ring at high RPM is more concerning.

That is at full throttle right?

Is it like a steady tone or ticking?

One way to check that sound is to just run a gallon of race gas and see if it goes away.

Race gas will kill that immediately if it's detonation and only occasional.

If it doesn't go away, it's prob. just a ring/piston/cylinder vibration that all 2T's do sometimes.

That's most likely it, but I'd still run the gallon of race gas to check to be sure.

If the race gas does fix it, you can do one of three things.

-run the race gas

-retard the timing

-bump up the main jet to the next richer size.

Its not realy either just a random noise I pick up on. Its not always there and it comes and goes as fast as you hear it. Im running the 180 main to be on the safe side. Ill try the race gas to see if that does it. I was thinking it was the usual 2 stroke noise as occasionally my CR250 did that but I was never really sure.

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You're prob. also fine as the detonation that damages engines isn't momentary but constant.

The heat that melts the piston isn't generated from a momentary detonation event,

but heat buildup from constant detonation as the throttle is wide open and the detonation doesn't go away.

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I think you're fine.

Maybe a just a touch of occasional tick each time the bike bogged down on the first vid but not really noticeable,

and that's normal imho when the engine momentarily bogs at low RPM with the throttle open.

You could see if that goes away by turning the A/S in 1/4-1/2 turn, but it sounded minor.

99% of that is just 2T pipe sound, but I thought I heard a touch or tick of minor ping.

In the second video you hear the 2T "ring" near the top of the hill.

I think that is the standard ring/piston/cylinder vibration that 2T's do

and every 2T I've ever had has had some "ring" at some RPM which

is just a characteristic of your rings/piston/cylinder clearance and vibration.

BB, listen to the second video and see if your "ring" is liike that.

Sounds like a normal 2T to me.

Anyone who ever has a question though can do the gallon of 100+ octane though and answer it quickly.

Just remember your engine has to be at the same temperature/load/outside air temperature to compare.

Yup that was it, just wanted to make sure it was all okay. Says I have to spread gas around before I can give you more.

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I think you're fine.

Maybe a just a touch of occasional tick each time the bike bogged down on the first vid but not really noticeable,

and that's normal imho when the engine momentarily bogs at low RPM with the throttle open.

You could see if that goes away by turning the A/S in 1/4-1/2 turn, but it sounded minor.

99% of that is just 2T pipe sound, but I thought I heard a touch or tick of minor ping.

In the second video you hear the 2T "ring" near the top of the hill.

I think that is the standard ring/piston/cylinder vibration that 2T's do

and every 2T I've ever had has had some "ring" at some RPM which

is just a characteristic of your rings/piston/cylinder clearance and vibration.

BB, listen to the second video and see if your "ring" is liike that.

Sounds like a normal 2T to me.

Anyone who ever has a question though can do the gallon of 100+ octane though and answer it quickly.

Just remember your engine has to be at the same temperature/load/outside air temperature to compare.

dang, you're the guy carvy! 👍

so what do you reckon, can i still lean out more, or am i already fine at that carb jetting? how 'bout changing to N3EJ needle (to lean out more) from the stock N3EW?

...again no access to race gas; by far the highest here is 96-octane. i may try the head mod (reduce squish) though as my next project

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Thanks

How does the bike feel now? Does it feel crisp everywhere?

Are you at about 1000ft? (The Phillipines are hard to pin down you know?)

I think your 45/#2 3EW/172 sounds about right for 1000ft. and 80F.

if you did go leaner I'd do it in small steps because I believe you're close right now.

I think your bottom is good with the 45.

If you want more mid response, I would do the #2 3CW before the #2 3EJ.

This is because the EW>EJ needle change primarily affects 0-1/4 throttle.

The W and J refer to the base diameter of the needle and doesn't affect the taper.

Your 45 is already lean there so you might be too lean there with the 3EJ.

If you went to the EJ, you might have to go back up to a 48 or turn the A/S in to 1/2-1 turn out total.

But moving the EW 1/2 clip leaner (#2 CW) will affect the whole range up through 3/4 throttle

without leaning out the 0-1/8 range so imho that's what you want if you stay with the 45 pilot.

The other alternative is to try the #2 3EJ and #2 3CJ, but keep in mind you might have to go back to a 48 pilot because of the leaner base of the J needle.

Make sense?

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Ah, see the no access to race gas now.

Regarding the head mod.

You may need to take some material out of the dome to maintain your compression when you shave the squish band down.

I think the reason that guys like Roland and I can get away with just a head shave to reduce squish without maintaining

chamber volume is that we ride above 4000ft and are down on compression to start with. If you're at 1000ft,

that might be too much compression without maintaining the original head volume.

Something to discuss with your machine shop.

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Thanks

How does the bike feel now? Does it feel crisp everywhere?

Are you at about 1000ft? (The Phillipines are hard to pin down you know?)

I think your 45/#2 3EW/172 sounds about right for 1000ft. and 80F.

if you did go leaner I'd do it in small steps because I believe you're close right now.

I think your bottom is good with the 45.

If you want more mid response, I would do the #2 3CW before the #2 3EJ.

This is because the EW>EJ needle change primarily affects 0-1/4 throttle.

The W and J refer to the base diameter of the needle and doesn't affect the taper.

Your 45 is already lean there so you might be too lean there with the 3EJ.

If you went to the EJ, you might have to go back up to a 48 or turn the A/S in to 1/2-1 turn out total.

But moving the EW 1/2 clip leaner (#2 CW) will affect the whole range up through 3/4 throttle

without leaning out the 0-1/8 range so imho that's what you want if you stay with the 45 pilot.

The other alternative is to try the #2 3EJ and #2 3CJ, but keep in mind you might have to go back to a 48 pilot because of the leaner base of the J needle.

Make sense?

Ah, see the no access to race gas now.

Regarding the head mod.

You may need to take some material out of the dome to maintain your compression when you shave the squish band down.

I think the reason that guys like Roland and I can get away with just a head shave to reduce squish without maintaining

chamber volume is that we ride above 4000ft and are down on compression to start with. If you're at 1000ft,

that might be too much compression without maintaining the original head volume.

Something to discuss with your machine shop.

you're the boss, carvy! haha!!! 👍:worthy: how much are we gonna pay you for this? :blah:

yup, we're about 100 m (300 ft) to 450 m (1500 ft) here in our playgrounds in manila. but sometimes, we trail ride in mt. pinatubo and mountain province. elevations at these areas are around 1500 m (5000 ft)

wait a minute, i'm uploading a vid (i think the bike runs crisp and sounds a bit like that) and a picture to show you a bit more... and how my plug looks like at constant WOT.

your explanation on the 3CJ was similar to BRM and the 172 main lean out was suggested by RCannon to make the top-end pull more as i complained about a flat top-end when i got the bike (stock main is 180)....and boy, does it pull the way RC described it haha! :busted:

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