Any other YZ300 YZ295 riders have issues at 1/3-1/2 throttle where it just will not run quite clean. I have treid chasing it with DEP/Stock pipe, different silencers, jetting all over the place JD kit red and blue needles the stock needle. My best setup is a 45p, blue pos 2 or 3 and 168 or 170 mn here I get good performance accept for the mid. If I hold 1/3-1/2 throttle it kind of cuts it wont run clean until I roll the throttle past this point then its great. It does not sound like a ping to me more of a sputter cutout. I am running 32:1 half C12 and half 93 pump 10% eth and its 95-100 degrees hot hot. Timing is .0009 like ev1 like most factory set yz250.

Could it have something to do with the powervalve being close to opening?Anyone else have this issue? Could it be I need staight race fuel or maybe a #8 slide?

The number 8 slide made mine nice...not so much in the range you are fighting, so I'll explain.

The 8 slide let me dial the pilot dead on the money. Far more close than even the stock 250 set up was. Thsi also helped the airscrew. This then left the needle to do what it does instead of helping an improper sized pilot.  The 8 slide is an amazing mod for a stock 250 or 295.  I think th e7 is just not the right size.

I put the #8 slide in my 300 and I wouldnt go back to a 7

So it sounds like for canon the #8 slide allowed him to select a proper sized pilot and jet from there not neccasarily solving a  mid throttle issue but giving him a good starting point for jetting.
S14 why did you go with the #8 slide?
Anyone else have this issue? Its not real pronounced unless you hold a throttle position leaving a jump face or on a straight.

I have the same issue, it's always been there just a little more pronounced with the 295. Not a huge deal but runs a little rich around 1/2 throttle, I'm at 45pj, 168mj, and n3cj needle.

rich around 1/3 throttle. I cound never tune it out with needles or jets. Mainly I did it to smooth the powerband out for the type of riding I do with this bike. With the #7 it was rich then it would hit hard once it got lean in the needle. Some people like this snap at 1/3 but I wanted a 295 that pulled hard of idle and rev to the moon with no powerband to hit at mid throttle. This is why I had the broad powerband with 110 olney. I couldnt be more happy with the power/tork of this bike. Now it hits hard everywere and I had to go with a 48t in the rear to get traction back. This will be perfect for ice racing/single track. Im running a 45 162 jd red #2 I think now and it was unreal the over rev this bike had. But I have a boat load of other things done to the bike other then the 295. I couldnt be more happy.
It pulls 5th as hard as it pulls 2nd. Way faster and lighter then my fully built 444.

s14 2510s said:

So S14 are you saying that you experience the same issue (uncleaness) that yz250_bm and I are expereincing at 1/3-1/2 throttle or were you looking to tone down the snap with the #8 slide?

I ride mx so my bike sees 98% track use and my issue is that when your trying to hold throttle positon when leaving the face of a big jump it is bothersome to experience that sputter knowing you have a long gap to cover and once your on take off face you cant change your mind your committed.

The same thing uncleaness at 1/3. I built this 250 to have a powerband simular to my 450. I didnt want to hit the pipe mid throttle like it use too. This 250 is kinda a experement. If I dont like it this winter I might sell it. I mainly ice race so I wanted to get the most tork, hp, and a huge overrev so I would be consistant. No matter how hard I tryed to tune the blip out at 1/3 throttle I always had a lean spot into the needle or rich spot coming off the PJ. I had RB do the carb mod and cut my slide to an 8. The bike is soo smooth now its crazy. Dont get me wrong I wasnt trying to tone the bike down any nor did it I just didnt want to mess with jetts all the time. The bike hits soo hard off idle it will almost loop out if your not carefull and revs like a train till its toped out. I had to put a 48t sprocket on just so the thing would hold traction in the summer. Im also running a boyesen rad  valve. Right now I couldnt be more happy with the bike. I just put the lower end together for the last time hopefully with wr1-5 and new everything besides the cases. Ice racing is real hard on lower ends because of the crazy traction you get. Its like twice the traction you would get riding a bike with slicks on tar. Yamaha put the #7 slide on because some people like the hit it gives but I personaly didnt like it and the #7 would work for everybody. Ive spent my whole summer messing with this 250. Ive spent 20hrs just messing with the engine to get it setup for how I ride. Hopefully it pays off in winter when I dont have to mess with brass as often. I have a 2 day trail ride next weekend and 2 harescrambles left that im going to race before winter. I just didnt want to spend my whole winter messing with this bike to figure out what works best with the 295.

S14 what did you pay to do your carb work and who did it? Or am i better off just buying a #8 slide?
where did you guys buy your slides at and what did they cost? thx

http://rb-designs.com/
He will cut your 7 to an 8 and do the carb mod. I had him install the finger turn air screw also. He has real fast turn around. Made my bike not run so notchy and it still screams in the top end. I couldnt be more happy with the bike. I actualy had to retard the timing to .004 It hits soo hard it wanted to loop out every time I would come off idle. I might go back to stock timing in winter when you can actualy use the extra hit. For single track .004 is perfect gave me a tad more power in the overrev and reduced the freight train hit. It hit soo hard at stock timing it was hard to even hold on to the bike. Im running a rekluse pro, trials tire at 8 psi with tubliss setup this might explain the crazy grip. I cant wait to beet the crap out of this thing in the woods for 3 steight days next weekend. bike pulls wr1-5 gears 1st just as hard as it pulls 5th. Imposible to stall, wont bog, I couldnt ask for much more.
Because it got cold and we lost the humidity I had to go up to a 48, jd blue #2, and a 165 with the air screw at 1 turn.

TakinaDirtNap, on 05 September 2010 - 09:51 PM, said:

Hey fellas, I have just built the YZ300 engine from top to bottom with rad valve and Gnarly pipe, 14oz Fly weight and i am experiencing the same as above........did this solve the problem dirtnap? will try the 48PJ, 172MJ and i have ordered the #8 Slider.

any input appreciated..........

I cant believe how lean you are all running on your big kits.. Of course mine is only a 285, so it may be different..Im running a 180-182 mj.. Tried a 175 almost blew it up.. 178 just wouldnt rev out... 180 feels good, but 182 feels even better..    

I took my main down by the same incriments as my pilot because I had to jet for elevation of 4000' Bike came stock with a 50p and 180main.....now I am running a 45p and a 175main second needle and I get a nice brown and dry plug. I could go a tad leaner but I will wait for my #8 carb slide to come in and start reading fresh plugs again.

BTW, I also messed with my premix ratios by just 25mls incriments of oil in 15 liters of gas.....got it bang on running 36:1 little or no spooge after taking off the reed cage an dipping a zyptie down the crank case to measure the oil level.

Edited by primerib108, 10 April 2012 - 10:15 AM.

bikedude127, on 10 April 2012 - 08:40 AM, said:

I came down from a 185 on my 265 to a 178 on the main jet. Must be the porting.

I remember I ended up going leaner on the MJ with the 295.

I'm using a 9 slide with a my 295. If yours is real bad you might need a 9 or more.

Try a HGS pipe, runs much cleaner than the DEP.

Does anyone mod the slides on the PWM carbs.? Mine is stamped a #6 and I see no replacements slides for the PWM compared to the PWK. Anyone have info on where the slide should be modded to make it leaner?

primerib108, on 10 April 2012 - 10:11 AM, said:

Gudday fellas

OK....tested the 300 again yesterday, running at sea level, 52PJ, 172MJ and now a brand new #8 Slider with the standard needle jet.........Still missing and a surge in power from PJ to NJ so guess too rich on the pilot in the bush, but was pinking/pre igniting after a caning in deep sand and back at idle....very frustrating as i want a safe tune for most conditions!
Have just put a 48 PJ in today but its still got a slight miss on the road but will know more once i get it back in the bush and the engines hot.........running outa patience with this......starting to look for a dyno tuner!
Any more suggestions appreciated, worried about cleaning up the miss by dropping the PJ then seizing it in sand?

might follow 'primeribs' lead and drop in a 178 MJ for saftey in the top end revs........

cheers

Edited by YZ300NZ, 14 April 2012 - 09:51 PM.

gudday..... finally in ball park with a 42PJ,172MJ, #8Slider, 1 turn out Air screw, std needle jet (atm!), std timing, still abit of run on at idle after a thrash so may change to thicker HG.

goodluck tuning!