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From 4 to 2 stroke???

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Hello, 

I have recently bought a crf250r from 2007, got some accesoires bought air filters etc. but my brother`s one blew up partly, the balance shaft and bearing blew, and partly the cases. and of my friends 4 stroke seized. im just scared that mine will too. and the cost of new piston, crank etc. i wanted to buy a 2 stroke because everyone says its cheaper. my dad said it isn`t because they break more often, but is this really true with good care? and the costs of a 2 stroke piston also arent that much cheaper. we can do everything ourselfs as far as maintenance replacing rods etc. if you do the maintenance yourself is a 2 stroke really cheaper? i was looking for a 250 2 stroke. if id where to use i will use 25-30:1. how much hours can the parts go with this ratio? and not race hours but the weekend warrior thats somehow fast rider. piston like 80 and crank maybe 200? i would like to see some opinions here! thanks in advance!

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If your worried about maintenance, sell your bike now no matter what it is. But yes a 2 stroke is easier and cheaper to work on. How long they last is hard to judge, don't neglect it and they all should last

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your dad is wrong.

 

a 4 stroke top end lasts 150-200 hours. and costs $1500 to rebuild.

 

a 2 stroke top end lasts 50-75 ish hours and costs $150 to rebuild.

 

25:1 is insanely lean.     40:1 is as much oil as you should put in there.

Edited by cdf450
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1 hour ago, cdf450 said:

 

 

25:1 is insanely lean.     40:1 is as much oil as you should put in there.

Can you please clarify this statement? 

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Lean and rich refers to your fuel:air ratio. NOT your fuel:oil ratio

 

25:1 is a lot of oil in the mix. Too much IMO.

 

A lot of efi 2 stroke machines run at 60:1 up to 100:1, depending on how hard the bike is screaming. There technically doesn't need to be much oil in your fuel. Just the bareeeeee minimum to keep it lubed, then maybe a little padding on top of that.

 

 

The more oil you're putting in your gas, the less overall gas your motor sees when the carb pumps a squirt in there... At 25:1, That squirt is now made up of lots of oil, and very little fuel. Even though the amount of air is always going to be the same. Therefore more oil means less fuel. Less fuel means it's lean. With more oil like 25:1 and less overall gasoline per ml, you'd need to richen the carb a tad.

 

 

Some people even have to lean the jets when the oil is decreased due to there being so much fuel (leaner carb setting for 50:1 versus 32:1.) That ones a bit confusing.

 

 

 

Btw it's not "insanely" lean. That may have been an exaggeration.

 

 

 

I am not 100% sure on this statement though: less oil and more fuel (80:1 ratios for example) actually allows the motor to run a bit cooler. Assuming jetting is correct. Is that true?

 

 

 

 

 

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Lean and rich refers to your fuel:air ratio. NOT your fuel:oil ratio
 
25:1 is a lot of oil in the mix. Too much IMO.
 
A lot of efi 2 stroke machines run at 60:1 up to 100:1, depending on how hard the bike is screaming. There technically doesn't need to be much oil in your fuel. Just the bareeeeee minimum to keep it lubed, then maybe a little padding on top of that.
 
 
The more oil you're putting in your gas, the less overall gas your motor sees when the carb pumps a squirt in there... At 25:1, That squirt is now made up of lots of oil, and very little fuel. Even though the amount of air is always going to be the same. Therefore more oil means less fuel. Less fuel means it's lean. With more oil like 25:1 and less overall gasoline per ml, you'd need to richen the carb a tad.
 
 
Some people even have to lean the jets when the oil is decreased due to there being so much fuel (leaner carb setting for 50:1 versus 32:1.) That ones a bit confusing.
 
 
 
Btw it's not "insanely" lean. That may have been an exaggeration.
 
 
 
I am not 100% sure on this statement though: less oil and more fuel (80:1 ratios for example) actually allows the motor to run a bit cooler. Assuming jetting is correct. Is that true?
 
 
 
 
 

runs cooler with more oil, also makes more power. not want a discussion here. but the crazy ratios nowadays is to keep the 2 strokes because of the environment and business.

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A crf250r isn't generally considered reliable by fourstroke standards, but making a comparison is pretty pointless unless you know what two stroke you are going to.

250 2 stroke

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5 hours ago, cdf450 said:

Lean and rich refers to your fuel:air ratio. NOT your fuel:oil ratio

 

25:1 is a lot of oil in the mix. Too much IMO.

 

A lot of efi 2 stroke machines run at 60:1 up to 100:1, depending on how hard the bike is screaming. There technically doesn't need to be much oil in your fuel. Just the bareeeeee minimum to keep it lubed, then maybe a little padding on top of that.

 

 

The more oil you're putting in your gas, the less overall gas your motor sees when the carb pumps a squirt in there... At 25:1, That squirt is now made up of lots of oil, and very little fuel. Even though the amount of air is always going to be the same. Therefore more oil means less fuel. Less fuel means it's lean. With more oil like 25:1 and less overall gasoline per ml, you'd need to richen the carb a tad.

 

 

Some people even have to lean the jets when the oil is decreased due to there being so much fuel (leaner carb setting for 50:1 versus 32:1.) That ones a bit confusing.

 

 

 

Btw it's not "insanely" lean. That may have been an exaggeration.

 

 

 

I am not 100% sure on this statement though: less oil and more fuel (80:1 ratios for example) actually allows the motor to run a bit cooler. Assuming jetting is correct. Is that true?

 

 

 

 

 

Right, and I agree with you, but I wasn't sure that's what you were saying by your post. You could always rejet it to not be lean, but I agree you don't need that much oil. I run 60:1.

Edited by 69fastback
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Right, and I agree with you, but I wasn't sure that's what you were saying by your post. You could always reject it to not be lean, but I agree you don't need that much oil. I run 60:1.


look i run 25:1 in my machines without problems i dont want a oil discussion here

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32:1 is pretty safe ratio with good oil, and good fuel. 

2 strokes are way cheaper to build, a helluva lot easier to work on (lot less parts in motor).  One of the downsides however is they burn a lot more fuel so the thumper guys will go a lot longer on a tank of fuel when trail riding. 

They are typically lighter though so easier to handle unless you get a handful of the power band in the wrong situation.  

@ 25:1 you wont have any mosquitoes around you for sure!  Let me know if you get it and run that ratio, I'll buy stock in NGK....

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Because I run 32:1 and my bike blows smoke and oil like a blown out oil rig. Congrats on starting another oil thread. You're wrong, no matter what.
 
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explain then why i dont have that problem? maybe your not on the pipe enough. maybe idling too long. maybe poor jetting.

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With good maintenance and proper jetting for running 25:1 a 250 two stroke should last about the the same between piston replacements as a 250f, probably need slightly more often crank replacements, and never need expensive head work.

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Keep in mind that too much oil leads to carbon buildup on the piston, in the power valve and in your pipe.  Carbon building up causes increased compression and hot spot both of which cause detonation.  Also carbon buildup can break off and score up the cylinder.  With modern oils there is no reason to be running anything near 25:1 and I'd argue that it will increase your maintenance and not reduce it.

 

Doc

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runs cooler with more oil 

 

Wrong 

 

 

I am not 100% sure on this statement though: less oil and more fuel (80:1 ratios for example) actually allows the motor to run a bit cooler. Assuming jetting is correct. Is that true? 

 

 Correct, assuming no jetting changes are made. Just playing with ratios has the opposite effect that riders look for. They reduce oil to reduce spooge. But they consequently richen the mixture, thereby reducing cylinder temps. Reduced temps = more spooge. The converse is obviously also true.

 

It's comical to me when members post here, asking for help. Then within a few posts, end up "teaching."

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