Reminder to rejet for colder temps

[450madman]

Ran great in 70° weather. Not so much at 35°.

[mx91a]

Yes sir!

Going from 70 to 35 degree weather will make your jetting about 4.5% leaner across the board. You would need to go +1 on the pilot, raise the needle by 1/2 clip and go up 2 main sizes to get your jetting back to where you were in the summer. Now if you were jetted a little on the lean side in the summer and made no changes now, well I think that pictures shows us pretty well whats happens!

[danhung11]

mx91a, where is that spreadsheet from? Is it interactive? Thank you!

[mx91a]

Originally posted by danhung11
mx91a, where is that spreadsheet from? Is it interactive? Thank you!

James Dean Jetting Guide!

[450madman]

Wow, thanks for the info.

[450madman]

Update. My buddy at the shop told me I was detonating, not running lean.

[Burns310r]

Running lean can cause detonation.

But i dont see detonation there....

I see a lean burn through the exhaust port, where the temps would be the highest.

Hence the hole. Cant believe it ran long enough to burn a hole.

[Meat]

hole.

[Burns310r]

uhhhhh thats what i said... hole....j/k

haha

thanks meat...

[mx91a]

I always thought detonation mostly damaged the top of the piston? Kind of looks like it ran lean, overheated (scoring on piston skirt), EGTs soared and finally the piston melted.

[Burns310r]

you are correct.


Detonation will damage the edge of the piston the most. It will look like little pits and the sharp edge of the piston will be erroded away.

[C-LEIGH RACING]

Read that piston real good Burns310r.
Neil

[Burns310r]

I see what you mean Neil.

I guess my thought process on this was that if it got hot enough to burn the hole in the piston, and erode the edges next to the hole, it should have been detonating all the way around the piston to some extent. It seems to be concetrated right at the exhaust port.


Share your thoughts on this Neil.

Thanks

[C-LEIGH RACING]

I'm not saying your wrong, not at all & I could stand corrected myself.
When you look & inspect it real close, every little detail of the damage done to that piston has a time when it happened.
For one, that black down the sides, it had to have somewhere to go, because if the wall of the piston was flat it would be worn off, so that piston had seized before the black was ever put in place.
It found its home down in the worn in seizure marks where the cylinder wall couldnt touch it.

The black got there, because the rings couldnt seal & everytime the piston was at TDC & the plug sparked, fire & burning fuel mix was blown past them down the side of the piston.
That process, super heated the pistons lower sides, a great bit more than was suppose to be happening from a normal operating engine.

Does some of that heat get past the piston & down into the crankcase, to some degree yes, so in turn, what does that do to the fresh charge getting ready to be blow up into the cylinder.

When the front of a piston is eat off like that, that is a sign of way to much high heat being blown out the exhaust port, so much that it melted the piston & blew it away.

There was a bunch of things happening to that piston & some were a bit early on before the cold weather ever got to it, so it wasnt just an instant cold weather jetting issue completely, but deto finely finished it off for sure.

Now who was it mentioned pump gas ??, because, it being to low of an octane can create the same looking type of damage, nobody did, but I'm just saying.

Center holes burnt threw a piston crown, normally come from ignition problems to some degree one way or the other, but whos to say, because I've never delt with it myself before, that to far of a retarded ignition setting could cause damage to the piston like he has, who knows.
In my mind, I could see it causing something, because when the piston is on its way downward before the plug sparks & causing higher heat later in the cycle, it would have to have some effect. From what I know though, retarded timing, that engine will tell you in short order through the power output, so some where or another that would get caught.

Lets study this some more guys, cause we are a dieing breed with these old 250Rs & when we are gone from just getting tired of dealing with problems, so is the ol 250R.
Now do any of you want that to happen & then the 4 pokes rule.
I dont for sure & when they turn my toes up & throw dirt on me, brothers I'll STILL BE TWO STROKE.
Neil

[450madman]

Here's some shots of the pistons top and other side. Makes sense about the excessive cylinder temp because my piston heated and swelled in the cylinder scraping both sides.
Before this happened (besides the cooler outside temps) I installed the new ESR 310-330 exhaust torque flange which is a smaller I.D. than the oem flange. ESR says I will gain torque without any loss on the top end with this flange. With the smaller I.D. I would think it may add a slight increase in egts. I'm not saying this had anything to do with the melt down. I'm just wondering what you guys think about going to a smaller I.D. on this flange. i'm thinking about machining this flange to oem specs.
My compression was around 170 and still breaking in. I used 91 octane @ 40:1 w/ Klotz R50. I plan on using 2 gal of race fuel to 3 gal of 91 and 1 step richer on the main. Thanks guys.

[450madman]

Top view

[Burns310r]

Yep with the top down pic, you can see the detonation happening.

Id say it was lean still. 170psi compression is nothing to shake a stick at, so your fuel shouldnt be an issue. Race gas is deff overkill.

[450madman]

My other buddy has a wide band a/f ratio guage and he thinks I can use to fine tune my R with it. He wants me to weld a bunge on my pipe. I've heard that they don't work well on 2 strokes because of the oil. He says his 02 sensor heats up so it should work.???
I failed to mention that when my piston melted down I was on a steep hill at the dunes and I lugged my bike because my son was on the back. I heard a pop through the exhaust as it died. I thought I had a low octane caused detonation not a lean one. So no race fuel, huh? I run a 180 main @ 4400 alt. I'll richen it up a couple and go from there.
Just don't want this happening again. I ended up with piston pieces filled crank bearings :(

[Burns310r]

I would say your lean. If you truly have 170psi compression, then good pump gas is fine. I would still run 91-92 octane to be safe, just because pump gas very's so much.


Hopefully Neil Chimes back in. He is the resident expert with motors. I trust his opinion over just about anybodys.

[mx91a]

So it melted while you were lugging it? Sounds like it is lean on the low end of the throttle range. What pilot jet and needle/clip position were you running? A 180 main is pretty healthy .

[C-LEIGH RACING]

When you installed that new exhaust flange, did you seal it up good, new gasket & new sealant on the pipe & then check it for leakage.

When the bike is sitting still when you first start it up & you got it real good & hot before you ride off, if you hold the throttle wide open, will it rev to the moon or get to a point & the rpm stay the same.


Either an air leak next to the exhaust, too low of an octane gas or somethings making it run lean at a certain time like when the engines pulling hard & using the most gas.
Neil

[450madman]

Exhaust flange seals great. The 2 piece pipes joint leaks a little but it has for a while. I always warm up my bike for the fear of cold siezing it. Revs to the moon.
I went from an 05 450R to my 86 R and never looked back.
Thanks for keeping the 2 strokes alive and for all your help.

[C-LEIGH RACING]

Ok, so it does rev to the moon, then that probably means it is really lean when under load & pulling hard.

Do you have one of those pretty little aluminum vents on the tank cap ??.

Believe it or not, I've never been one to plug chop & jet a carb. Just something I never had to do, because when you run 2 stroke karts & sitting there tweeking those adjustment screws, your ears learn the points at were to stop leaning it out before you kill an engine.

When the engine will rev to he moon just sitting, once your out riding & that engine is working hard, moving you & the weight of that bike, it is in serious trouble, because at that point that carbs not providing enough fuel to keep the piston & cylinder cool & keep them from sticking together.

Use the main jet, as a govenor to hold the engine back, from revving out so far & then when your out riding, it will be providing enough fuel to cool anything moving inside the engine when it is really working hard.

It would be hard for me, to try & tell you how to jet by ear, what to listen for from the engine & not something you'll just pick up after a time or two of doing it, but those ears wont lie once you get it figured out.

Never ever jet an engine out (lean) for peak hp, not unless your playing with it on a dyno just to see the results, because that carb & those jets are providing the life blood that is keeping those moving parts smoothly sliding past each other in a 2 stroke engine.
Neil

[450madman]

Finally got my bike all put back together. While breaking the motor in I found out that my petcock hasn't been working correctly. I think a combo of not enough fuel from dirty screens on the petcock and possibly a little lean on the jetting is what melted my piston down.

[KM250R-BDTM]

Now the first picture, and the second & third picture posted tell the story. Look at the pictures, what would cause a pistons outer edge at the exhaust side to melt away and burn a hole through one of the pistons thickest section?

Here are a few, the answer can be found in one or more of these:

• Main crankshaft Seal leak
• IGN advanced too far
• Compression set too HIGH
• Bad Fuel or not enough Octane
• UCCR way off or too high for the Octane level used
• Coolant leak at the exhaust side (head o-rings or through exhaust flange threaded holes)
• Exhaust outlet restricted, pressure too high (caused by exhaust reducer)

The damage is considerable enough to say a major negative occurance caused the failure, beyond the point of 1-2 sizes too lean due to weather change alone.