yz250 jetting

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primerib72
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Re: yz250 jetting

Post by primerib72 »

thirtyseven wrote:My heart is going all pitter-patter, will be a cool machine.
Thanks for all the congrats fellers. I wanted a suitable replacement for brutus and it came down to either the 300xc or the yz295....I am pretty tight with my $$$ so the Yammy won.

Keeping the dream alive Howard :thumbsup:
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Re: yz250 jetting

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It will be really interesting how the powerband you chose works!
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Re: yz250 jetting

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Just a follow-up to the yz295 jetting. Did a few things that made the jetting process easier by retarding the timing by 1 degree and threw in a #8 carb slide (leaner) made it hum along with a nice crisp throttle and linear power curve all the way threw the revs....revs to the moon now and no obnoxious hit. Also cut down on the spooge a lot running 35:1 premix.

I think the katoomers run the same carb at if you are running a #7 slide then I highly recommend the #8 especially for our altitudes.
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Re: yz250 jetting

Post by dirtyboy »

primerib72 wrote: Also cut down on the spooge a lot running 35:1 premix.
:eek: You are running 35:1 premix? That's a lot of oil for a 300. :eek:

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Re: yz250 jetting

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dirtyboy wrote:
primerib72 wrote: Also cut down on the spooge a lot running 35:1 premix.
:eek: You are running 35:1 premix? That's a lot of oil for a 300. :eek:
Maybe it's just a Yamaha thang :D The manual wants 32:1 :crazy:

I tried running 43:1 (eric gorr recommended) but it didn't run quite right......starting from 32:1 I dropped the incriments of oil gradually where I found the bike makes good power and ran smooth at 35:1. Granted I don't lug it too much and like to be on the pipe most of the time. Might have to tweek it a bit once I get on the trails again and how my riding effects the performance of the bike.
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Re: yz250 jetting

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primerib72 wrote:Just a follow-up to the yz295 jetting. Did a few things that made the jetting process easier by retarding the timing by 1 degree and threw in a #8 carb slide (leaner) made it hum along with a nice crisp throttle and linear power curve all the way threw the revs....revs to the moon now and no obnoxious hit.
I hear that retarding the timing also makes it smoother on the bottom end... did it make any difference down low? One complaint I have with my CR is its tall first gear, and trying to get started on a rocky uphill is a pain... so increasing the usable revs down low would help. I've also heard that retarding the timing gets the pipe hotter in the top end... that alone might help with spooge.

I plan to mess with my bikes timing this spring to try to smooth out the hit. Glad to hear its worked for someone else :thumbsup:
Ian
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Re: yz250 jetting

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Abeo wrote:
primerib72 wrote:Just a follow-up to the yz295 jetting. Did a few things that made the jetting process easier by retarding the timing by 1 degree and threw in a #8 carb slide (leaner) made it hum along with a nice crisp throttle and linear power curve all the way threw the revs....revs to the moon now and no obnoxious hit.
I hear that retarding the timing also makes it smoother on the bottom end... did it make any difference down low? One complaint I have with my CR is its tall first gear, and trying to get started on a rocky uphill is a pain... so increasing the usable revs down low would help. I've also heard that retarding the timing gets the pipe hotter in the top end... that alone might help with spooge.

I plan to mess with my bikes timing this spring to try to smooth out the hit. Glad to hear its worked for someone else :thumbsup:
You are right on about the timing......pipe gets much hotter and in essence burns the oil mixture more effectively and reducing spooge. It didn't noticed much down low but it sure smoothed out the mid-top hit and gives you more over rev. My 295 pulls like a mule....if I lost or gained some it would be hard to tell. I hear that the DEP pipe works wonders for low end on Japanease bikes so maybe consider that as well.

I made a 2 stroke timing tool from and old spark plug and a digital dial gauge....on Yamahas 1 degree equals 3 thousands of an inch (.1mm) so rotating the stator by that small of an increment is required. You are more than welcome to use it.
Last edited by primerib72 on Sat Apr 14, 2012 8:45 am, edited 1 time in total.
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Re: yz250 jetting

Post by axel99 »

Lets see a few pics and a short how to writeup or links on this fancy timing adjustment tool. :thumbsup:
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Re: yz250 jetting

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axel99 wrote:Lets see a few pics and a short how to writeup or links on this fancy timing adjustment tool. :thumbsup:
Ask and you shall receive :D

Here is my hillbilly deluxe design of my timing tool that I made from a used spark plug and a digital dial gauge. Here is a link http://rd400.petercamburn.com/2008/08/2 ... iming-kit/ for a how to make your own....any dial gauge will work but recommend getting a decent quality one and can measure in thousands of an inch. I found I didn't need to add the extension to make mine work considering I have a liquid cooled bike.

Image

Here is a quick write-up form a site (no credit for me on this) on the variables of changing your timing, and for our Honda friend a little bit of info to consider at the bottom;

AFFECTS OF THE IGNITION TIMING

Here is how changes in the static ignition timing affects the power band of a Japanese dirt bike. Advancing the timing will make the power band hit harder in the mid range but fall flat on top end. Advancing the timing gives the flame front in the combustion chamber, adequate time to travel across the chamber to form a great pressure rise. The rapid pressure rise contributes to a power band's "Hit". In some cases the pressure rise can be so great that it causes an audible pinging noise from the engine. As the engine rpm increases, the pressure in the cylinder becomes so great that pumping losses occur to the piston. That is why engines with too much spark advance or too high of a compression ratio, run flat at high rpm.

Retarding the timing will make the power band smoother in the mid-range and give more top end over rev. When the spark fires closer to TDC, the pressure rise in the cylinder isn't as great. The emphasis is on gaining more degrees of retard at high rpm. This causes a shift of the heat from the cylinder to the pipe. This can prevent the piston from melting at high rpm, but the biggest benefit is how the heat affects the tuning in the pipe. When the temperature rises, the velocity of the waves in the pipe increases. At high rpm this can cause a closer synchronization between the returning compression wave and the piston speed. This effectively extends the rpm peak of the pipe.

HOW TO ADJUST THE TIMING

Rotating the stator plate relative to the crankcases changes the timing. Most manufacturers stamp the stator plate with three marks, near the plate's mounting holes. The center mark is the standard timing. If you loosen the plate mounting bolts and rotate the stator plate clockwise to the flywheel's rotation, that will advance the ignition timing. If you rotate the stator plate counterclockwise to the flywheel's rotation, that will retard the ignition timing. Never rotate the stator plate more than .028in/.7mm past the original standard timing mark. Kawasaki and Yamaha stator plates are marked. Honda stators have a sheet metal plate riveted to one of the mount holes. This plate insures that the stator can only be installed in one position. If you want to adjust the ignition timing on a Honda CR, you'll have to file the sheet metal plate, with a 1/4in rat-tail file.
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Re: yz250 jetting

Post by axel99 »

Looks simple and accurate. I like it. Sure are a lot of "in your garage" tuning possibilities to play with on a 2T between X-Dimension(port timing and squish changes) and ignition timing. Haven't wrapped my head around how it all works together but it is really interesting. Good to hear you're having successes in getting the bike tuned to your liking. :cheers:
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Re: yz250 jetting

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Very accurate and easy to do. I found out my bike had slightly advanced timing than what the manual states.....it was .008 instead of the recommended .007. I forgot to mention a good reason to retard the timing was because of using pump gas also, I use Husky 94 octane but it still had a bit of tendency to ping under load at mid range. This is a common issue with yzees unless you are running race gas. I can't say the same for different makes and there is a good write-up about this mod in the Yamaha 2-stroke section of thumpertalk.
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Re: yz250 jetting

Post by steve-o »

primerib72 wrote:Very accurate and easy to do. I found out my bike had slightly advanced timing than what the manual states.....it was .008 instead of the recommended .007. I forgot to mention a good reason to retard the timing was because of using pump gas also, I use Husky 94 octane but it still had a bit of tendency to ping under load at mid range. This is a common issue with yzees unless you are running race gas. I can't say the same for different makes and there is a good write-up about this mod in the Yamaha 2-stroke section of thumpertalk.
look through the technical section on fuel recommendations, there are some very good reasons to not use that ethanol enhanced fuel. shell gold is the only way to go. if trailguy reads this and replies consider yourself lucky as it will save you a tonne of time searching archieves.

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Re: yz250 jetting

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I did here about the issues with using ethanol blends. Rumor has it that Husky doesn't use the 10% blend, on their pumps it states "up" to but never indicates an exact amount but my friend indicated usually it is much lower. I did make that inquiry with Eric Gorr too while on the phone with him before I sent my head to get machined. He mentioned his porting option is ethanol friendly if I decide use it but I had to clearly indicate that on the work order when I sent the cylinder. From what I can gather the ethanol makes it harder for the premix oil to essential mix with the gas correct?
Last edited by primerib72 on Sat Apr 14, 2012 2:21 pm, edited 1 time in total.
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Re: yz250 jetting

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primerib72 wrote: I made a 2 stroke timing tool from and old spark plug and a digital dial gauge....on Yamahas 1 degree equals 3 thousands of an inch (.1mm) so rotating the stator by that small of an increment is required. You are more than welcome to use it.
Once I get my bike back together, I'll take you up on that :)

Wow, that's a bunch of good info on timing! My bike hits hard and signs off on top, which probably has to do with the gnarly pipe, stock MX porting, poor jetting (damn TMX), and the stock timing advance... sounds like retarding the timing would make my bike a bunch more fun to ride in the trees.
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Re: yz250 jetting

Post by yamaha295 »

Could someone be so kind as to PM me the proper carb set up for our elevation? Building my YZ295 this week and would love to skip the step of messing around with a bunch of different sized main and pilots jets.

I can offer cold beer!

Thanks in advance

Drew

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