YZ250 Muffler Chop Question

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7/13/2021 12:23 PM

Do people do this? I'm mostly bored and want to tinker, but I do wish the bike had a higher pitch sound to it. I'm satisfied with the power so I wont bother with an aftermarket muffler until I do the whole pipe (if ever).
I also am assuming this does not affect performance. If it does, how so?
My only concern is about making sure the bike is running properly. Will 3-6 inches, or just enough to tuck it back behind the plate, cause any jetting issues? Any other thoughts?
Slight chop? Leave it alone?

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7/13/2021 1:28 PM

I would think this would change the power to the low end a bit. I use a shorty silencer on my YZ125's to get more bottom end.

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7/13/2021 1:49 PM

Moto520 wrote:

I would think this would change the power to the low end a bit. I use a shorty silencer on my YZ125's to get more bottom end.

I'm probably not going to be into that then. The bike tends to fall flat up top so i was already considering dropping a tooth on the rear as it is. I prefer to ride it up a little higher anyways. Good to know. I just want it to get that crispy, dingy sound lol.
Not worth sacrificing top end though. I have seen that people tend to use the PC pipe for some more up top.

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7/13/2021 2:26 PM

Go BIG (small?) or go home !!!Photo

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Powerband in every gear !

7/14/2021 4:30 AM

Shortening the muffler will lose a little top end with a gain in bottom-mid. When I shortened the silencer on my 2010 yz250 I didn't notice a difference in sound but they came with shorter silencers standard than the more recent ones do

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7/14/2021 7:14 AM

chump6784 wrote:

Shortening the muffler will lose a little top end with a gain in bottom-mid. When I shortened the silencer on my 2010 yz250 I ...more

Yeah that's what I've been seeing myself. I think it's just time to quit being ghetto and order an exhaust if I want the sound lol.

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7/14/2021 7:19 AM

Highher pitched sounds come from smaller engines. You cant make a 250 sound like a 125

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7/14/2021 11:02 AM

kb228 wrote:

Highher pitched sounds come from smaller engines. You cant make a 250 sound like a 125

really? i thought i could make it sound like a cobra 50 dude! thanks for saving me all the headache.

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7/14/2021 9:10 PM

If you want better sound without a big change in power, keep the stock pipe and go with a PC (or other aftermarket) silencer. You can alter power slightly with the length (304 vs R304 in the case of PC, but more than anything you’ll get a crisper sound.

My favorite combo on my last two-stroke (02 CR250R) was a stock pipe with a PC silencer.

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7/15/2021 7:00 AM

PNWRider wrote:

If you want better sound without a big change in power, keep the stock pipe and go with a PC (or other aftermarket) silencer. ...more

Yeah but wont the r304 also move the powerband some? I'm kind of struggling with this. The bike needs to stop falling flat up top. I was thinking about dropping a tooth off of the rear but then I see that everyone adds a tooth to help with shift points. Maybe dropping a tooth and running the r304 would be a nice happy medium.

Truthfully, I haven't been on a bike in 3 years until last weekend. So at this point I am just looking to get back (close) to speed and then going from there. I'm working on suspension and fitness now but my riding is going to change so much in the next few months that I may want to mod the bike in other ways. That's why the chop was appealing cause its free lol. I'm just looking to up the smiles with that nice sound for right now with more useful mods to come as needed.

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7/15/2021 2:18 PM

If your bike is already falling flat on top, a shorter muffler is going to make that worse.

You need to ensure your jetting is correct also. A main jet that is too rich or too lean will not allow the bike to rev out cleanly and pull as far as possible.

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Powerband in every gear !

7/15/2021 2:29 PM

FGR01 wrote:

If your bike is already falling flat on top, a shorter muffler is going to make that worse.

You need to ensure your jetting ...more

Unfortunately I don’t know the first thing about jetting and such. It’s completely stock, 2021 with about 1 hour on it aside from the break in. I’m at 200 ft elevation and it’s summer. Thoughts? Too lean? Spark plug looks great but that’s not the only piece of the puzzle I know.

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7/15/2021 2:56 PM

FGR01 wrote:

If your bike is already falling flat on top, a shorter muffler is going to make that worse.

You need to ensure your jetting ...more

Owen H wrote:

Unfortunately I don’t know the first thing about jetting and such. It’s completely stock, 2021 with about 1 hour on it aside ...more

Pro circuit and FMF have pretty good Jetting sheets on their websites. I've found them to work pretty well with a stock system after you do some fine tuning.

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Unleaded tastes a little tangy. Supreme is kinda sour, and diesel tastes pretty good.

7/15/2021 10:01 PM

Rickyisms wrote:

Pro circuit and FMF have pretty good Jetting sheets on their websites. I've found them to work pretty well with a stock system ...more

I was glad the topic came to jetting because I really feel like the bike generates more heat than it should. This could be entirely mentally fabricated though since i've never owned a YZ250. I would be curious to go up a size in whatever jet handles 1/2 - WOT. Yes, I'm that ignorant. Yes, I'm reading on my spare time lol.
I see many good things about the Suzuki needle too. I would like to drop in a richer setting just to see what it's like. It is unusually flat up top. However, I have too many unknowns to draw conclusions right now. Please share any info/links you think will get me going (:

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7/15/2021 10:12 PM

I do want to restate that after roughly 1.5-2 hours total time (including break-in) on the bike, the plug is looking exactly how it should from what I understand.
Dark, not burnt, not wet. Goldish color on the ring around the electrode. dark brown electrode tip. Consistent coloring on the ground electrode with a little area by the bend that barely shows any difference.
According to a guy named cameron on youtube, its grrrrrrreat lol.

I'm also 210 lbs so maybe the bike just isnt a rocket with bigger guys on it. who knows.

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7/16/2021 9:59 AM

Before getting into jetting specifics, you'll have to tell us what fuel, oil, and ratio your are running as all this directly affects your jetting.

Also, there are tons of threads on here about YZ250 jetting.

Generally speaking, the stock YZ250 jetting is pretty damn good. you just need some fine tuning for your specific fuel and conditions.

The main jet handles 1/2 - WOT. Stock is a 178. It's easy enough to swap out for experimenting. Get a 175, 180, and 182 and try them out. Takes about a minute to swap.

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Powerband in every gear !

7/16/2021 10:14 AM

FGR01 wrote:

Before getting into jetting specifics, you'll have to tell us what fuel, oil, and ratio your are running as all this directly ...more

I've done some reading this morning at work. Things are a little slower this morning. I've determined that I would probably like to stick to altering the main jet only and, like you said, the 180 and 182 are going to be of interest. I'm really interested in increasing the longevity of the bike too, not just the high rpm sign off.

The bike runs awesome everywhere. It could just be me. If that's true then I'll look into some power mods but I remember my 2014 250SX being STUPID fast. Like night and day different. I wouldn't mind if this one was little more.. pronounced up top.

Anyways, I run castor 927 @ 32:1 with 93 Pump gas. Standard plug - BR8EG. Only other fuel options near me are AvGas (100LL) and 90 Oct ethanol free. I don't let the bike sit much so I don't worry about ethanol really.
Do I need to lean or richen for colder weather? I assume richen since we're increasing the specific oxygen content.

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7/16/2021 11:21 AM

YZ250 is known to be borderline lean jetting when running pump gas, especially in colder temps or lower elevations which both lean the bike out. The 2011 and newer are not quite as borderline because they have the richer N3EW needle and lower compression head. But yeah, I'd try a 180 or 182, especially as the temps drop in fall/winter.

A really good mod is to get the head cut and reshaped for pump gas. You can get the squish tightened up while still keeping the compression where it needs to be for the 93 gas. It makes the bike run cleaner and makes jetting easier.

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Powerband in every gear !

7/16/2021 11:29 AM

FGR01 wrote:

YZ250 is known to be borderline lean jetting when running pump gas, especially in colder temps or lower elevations which both ...more

"A really good mod is to get the head cut and reshaped for pump gas"

Would you elaborate a little more or drop a good explanatory link for this? I'm not very familiar with this idea personally.
Who does it? Why do it? Sounds interesting.

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7/16/2021 11:44 AM
Edited Date/Time: 7/16/2021 11:47 AM

FGR01 wrote:

YZ250 is known to be borderline lean jetting when running pump gas, especially in colder temps or lower elevations which both ...more

Owen H wrote:

"A really good mod is to get the head cut and reshaped for pump gas"

Would you elaborate a little more or drop a good ...more

The squish band clearance is too large from the factory. Off hand if I remember correctly a lotof them are in the 80 thou range. They should be in the 50 thou range.

The larger than optimal squish clearance leads to a less efficient combustion event. This is why a lot of YZ's ping on pump gas from the factory.

If you have access to a lathe or mill you can easily measure your squish, and then remove the desired amount to put you in the desired squish clearance range by removing material from the face of the head. It would be smart to take some material back out of the bowl to get the volume back closer to stock, otherwise you will decreased combustion chamber volume and thus increasing compression.

I took the desired amount off the face of my head and then just spun it on the lathe to while holding some emory on my finger to get the volume back in the bowl so i didnt have to worry about following the contour as much with a cutter, just measured volume a few times along the way because it was a bit slower going. Or send it to somebody and pay them 100$ to do it. Down the road I sent the cylinder and head to Tom morgan for some work and he didnt have any complaints about my "craftsmanship" .

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7/16/2021 12:01 PM

FGR01 wrote:

YZ250 is known to be borderline lean jetting when running pump gas, especially in colder temps or lower elevations which both ...more

Owen H wrote:

"A really good mod is to get the head cut and reshaped for pump gas"

Would you elaborate a little more or drop a good ...more

dmm698 wrote:

The squish band clearance is too large from the factory. Off hand if I remember correctly a lotof them are in the 80 thou ...more

Do i send the head, gasket, and piston or just the head or what? It seems very bike specific but I've never done it so I don't know. Definitely important to get that right. I never thought of that.

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7/16/2021 7:30 PM

The 2014 250sx had a very strong motor, your yz is going to be a couple hp down on it. If you are looking for more top end pull get a dep pipe and dep standard length muffler. Bike revs forever and makes more power than stock all the way through.
I always liked the 182 main jet in mine too

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7/17/2021 8:19 AM

Owen H wrote:

Do i send the head, gasket, and piston or just the head or what? It seems very bike specific but I've never done it so I don't ...more

https://rb-designs.com/rb_designs_llc_017.htm

Follow these instructions and send your test solders in with your head.

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7/19/2021 6:27 AM

Thanks for everyone helping me. I dropped the factory included 180 main in last night and took it for a test pull between rains.

It mostly feels the same. I'll be curious to see if there's going to be a noticeable difference in heat generation or if I'm just not used to the bike. I do know one thing though, I do not want a short muffler. It's unanimous that this is detrimental to top end. So we got that figured out lol.

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7/19/2021 8:50 AM
Edited Date/Time: 7/19/2021 8:52 AM

Owen H wrote:

Thanks for everyone helping me. I dropped the factory included 180 main in last night and took it for a test pull between ...more

Go with either a PC 304 or FMF Powercore. Stock or close to stock length, will sound better, and will fit whichever pipe you decide to go with later.

My personal preference is PC, but both are good.

As far as the running hot and lack of top end, like the others have said-check your squish and have the head cut/reshaped if needed. Run ethanol free pump or T2.

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7/19/2021 10:09 AM

Owen H wrote:

Thanks for everyone helping me. I dropped the factory included 180 main in last night and took it for a test pull between ...more

PNWRider wrote:

Go with either a PC 304 or FMF Powercore. Stock or close to stock length, will sound better, and will fit whichever pipe you ...more

Would you step down to 90 octane just to be eth free? I imagine I am going to encounter knocking but I really am out of my realm here. I'm more of a car/4-stroke guy. I can pretty much guarantee that I'm not doing any head work until we get some consecutive bad weather in the winter. I wanna RIDEEEEEEEE hahaha.

For some reason I never thought about the standard length 304.. That may get the sound I desire, shed some mass, and preserve (boost?) the top end of the range.

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7/19/2021 10:57 AM

Owen H wrote:

Thanks for everyone helping me. I dropped the factory included 180 main in last night and took it for a test pull between ...more

PNWRider wrote:

Go with either a PC 304 or FMF Powercore. Stock or close to stock length, will sound better, and will fit whichever pipe you ...more

Owen H wrote:

Would you step down to 90 octane just to be eth free? I imagine I am going to encounter knocking but I really am out of my ...more

Any chance you could get your hands on leaded 110? A gallon or two mixed with 90 ethanol would treat that bike good and resist pinging.

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Unleaded tastes a little tangy. Supreme is kinda sour, and diesel tastes pretty good.

7/19/2021 11:02 AM

PNWRider wrote:

Go with either a PC 304 or FMF Powercore. Stock or close to stock length, will sound better, and will fit whichever pipe you ...more

Owen H wrote:

Would you step down to 90 octane just to be eth free? I imagine I am going to encounter knocking but I really am out of my ...more

Rickyisms wrote:

Any chance you could get your hands on leaded 110? A gallon or two mixed with 90 ethanol would treat that bike good and resist ...more

Well I can get 100LL, but thats it.

I'm not really interested in getting in a situation where I'm ordering race fuel for 10/gallon and then getting destroyed on shipping. Where I live sucks for anything other than being fat and farming.

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7/19/2021 11:49 AM

Owen H wrote:

Would you step down to 90 octane just to be eth free? I imagine I am going to encounter knocking but I really am out of my ...more

Rickyisms wrote:

Any chance you could get your hands on leaded 110? A gallon or two mixed with 90 ethanol would treat that bike good and resist ...more

Owen H wrote:

Well I can get 100LL, but thats it.

I'm not really interested in getting in a situation where I'm ordering race fuel for ...more

The problem with AVgas is the Oxygen content, so mixing that with pump may affect your jetting even more. VP's site says Do It Best-RSC is the only VP dealer around. Don't know how far they are from you though.

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Unleaded tastes a little tangy. Supreme is kinda sour, and diesel tastes pretty good.

7/19/2021 11:58 AM

Seems like everything else is a band aid at best.

I'm going to send the head off within a few weeks and run pump trash and smile away lol.

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