Mo' Better ride report...03 YZ250

[SpectraSVT]

Mo' Better Porting ride report...03 YZ250

A couple of people asked for a ride report after the Eric Gorr porting so here it goes. I took the bike out today at a local track and have come away with mixed feelings. First the good, the bike is faster. The midrange comes on hard and fast and it revs forever before topping out. Great over-rev. The bike responds instantly and I didn't have to gather as much speed to do some obstacles. It picks up super quick and gets up to speed in no time. This may not mean much but I drag raced some much faster riders on 450's up a hill and actually pulled them. They would leave me the very next corner but I felt fast for about 4 secs! I could never pull the 450's before up this hill.

Now the bad. I seem to have lost alot of bottom end. I originally did this so I could shift less but now I shift more. Bottom end is almost non-existent. Could be just jetting, I couldn't tell after 1 ride. I messed with air screw but had no luck just made the bike more zippy. I practiced starts a few times and if I didn't keep it reved, it would bog out in 2nd until I got into the midrange and it would pull in 2nd all the way down the start straight. Negative #2 would probably be that its too responsive. I ended up shifting twice before jumps just to get the bike to calm down a bit so I could hit a tricky jump. It was cool when I was fresh but when I got tired it was too much bike for me.

I am definitely gonna try raising the needle to try and take some of the snap out of the midrange. I don't know what to do about the pilot just yet becuase the bottom end is a major disappointment so far. Maybe when the main is set right I'll start with the pilot fine tuning.

 

[jimyz]

What are you comparing the bike to? Or what are you coming off of? I came off an 04 yz250f and think the diff is huge. There's pro's and con's about the the 2s and 4s thing, I like them both. I currently like the 2s's- jim

 

[SpectraSVT]

I'm not coming off anything but the bike I'm riding. I had the Eric Gorr Mo Better Porting done 2 weeks ago. I'm comparing it to my once stock 2003 YZ250.

 

[pro2k]

Any updates with your biike?

 

[Rich Rohrich]

Spectra - Did you have it set up for pump fuel or race fuel ?

 

[SpectraSVT]

I requested pump fuel...why?

I have raised the needle up 2 clips because it was surging while practicing starts...I don't want it running lean. I am gonna buy a 42 pilot and 40 pilot and hopefully one of those will give me my bottom end back. I am currently running a 45 pilot..before porting I used a 48. I could clutch it out of corners in 3rd before but now it just dies. I wasn't sure how lean its supposed to go.

 

[RM_guy]

I went from a 48 to a 42 pilot after the Mo Better porting and it helped a lot. V-Force reeds will help too.

 

[SpectraSVT]

I went from a 48 to a 42 pilot after the Mo Better porting and it helped a lot. V-Force reeds will help too.

Thx...I'll be trying it out again this saturday. I didn't buy the leaner pilots ahead of time so I wasn't able to fix it right away. I'm hoping its better. Was your Rm a huge difference from stock? I'm scared of the bike again! Not sure if thats a good thing.

 

[Rich Rohrich]

I requested pump fuel...why?

Getting the jetting correct is the best way to maximize the gains but you will ALWAYS sacrifice some low end performance if you insist on pump fuel compatability with your engine mods. There is no way around that.

Building an engine that can retain pump fuel compatability really limits the amount of compression you can run and forces compromises in the way the head and port time areas are modified. Cylinder pressure and low end torque go hand in hand, and engines can't live on pump fuel and high cylinder pressures so you lose some low end as a result. The jetting hassles that come with pump fuel are well documented out here.

With good fuel there are a lot more options in terms of power spread.

 

[SpectraSVT]

So basically I requested the wrong thing? I should have requested race gas tuning and switched to race gas permanently for low end? I must have missed something....should have looked at the site better. Oh well...too late to change it now. Does tuning it for pump fuel take away the low end power it had stock? I assumed mo better meant mo better everywhere...I still have to change the pilot so hopefully the low end is not completely gone.

 

[Rich Rohrich]

So basically I requested the wrong thing? I should have requested race gas tuning and switched to race gas permanently for low end?

No, if what you were looking for was low end and the ability to run pump gas you probably should have requested low end specific porting.

Pump gas compatability just makes it tough to get gains everywhere. Depending on the engine you usually have to trade off something if you want to run cheaper gas. If you want it to run hard on top, some low end will usually get sacrificed for the pump gas tuning. The opposite can also be true.

From a performance standpoint pump gas doesn't have a lot going for it .

The good news is, if you want to switch to better fuel at some point it usually just takes some head mods to fatten up the low end.

 

[RM_guy]

...Was your Rm a huge difference from stock? I'm scared of the bike again! Not sure if thats a good thing.

My bike already had fairly good low end and it was a bit better after the porting...and even better with the reeds. The stock engine and a midrange that came on strong and pretty much no over rev. I am a shortshifter and rarely over rev but even I noticed it! After the porting the mid was smoothed out and it revs out nicely.

Jetting can make a big difference but you have to be patient and work through it.

Good luck

 

[bclapham]

spectra,

1. check your powervalve is operating properly.

2. you can always up the compression a bit. if you want to try and get a bit of bottom end back, try a thinner base gasket from cometic.

the problem is, the YZ set the standard with the 250 engine. Suzi and Kawi have copied their specs, so its not trivial to improve on the standard "Best" porting setup. Of course, you can change them all together when looking for either bottom or topend motor.

 

[Nevada Sixx]

maybe you can try adding a high compression gasket kit...
as for having to shift more,, maybe you can go down a tooth on your rear sprocket, and add a torq pipe.

 

[Rich Rohrich]

spectra,

1. check your powervalve is operating properly.

Bruce brings up a VERY important point here. This discussion is based on the assumption that A) your jetting is correct and B) your power valve drive mechanism is functioning properly.

If you haven't done it already, it's worth the time to verify that the powervalve has smooth action and is functioning properly before you go any farther .

A malfunctioning power valve will have a much greater influence on the low end than the difference between race gas and pump gas porting.

 

[SpectraSVT]

The powervalve was in a different position after the porting than what it was when it was sent out. I had assumed Eric or whoever does the porting changed it. It was almost hitting the piston when I sent it out. I will first get the jetting right down low before I pass judgement on the low end. The rest of the powerband is pretty fast and hard to control. Perhaps I should have researched it more. I just heard so much good stuff about the mo better that I didn't look into more than a few searches. I didn't read anything in those posts about the diff. between pump and race gas. I will post again after this weekend. If jetting is right and still no low end I may just get a gnarly pipe or PC2 pipe to move some of it lower. Like the ol' saying...you don't know what you got til its gone!

 

[bclapham]

SVT- sounds like you need to check the PV again before you touch anything else.

the PV should be right up against the piston (it wont touch) and the two barrel sub port PVs will be blocking off those ports also. Then, swing the actuator arm up, and you will be able to see them all open.

 

[SpectraSVT]

Alright...I checked the PV and couldn't tell where it was at. I took the PV cover off and turned the arm and it seemed to pop loose. Not sure though. Must have been stuck...its seated correctly now. I also changed the pilot down to a 42 and the bike didn't like it. Wouldn't idle low...just revved high and wouldn't go any lower. SO 45 must have been right to begin with. I won't know til 2morrow how it rides. I don't know how the PV would have gotten stuck or if it even was stuck at all. Just heard a slipping noise and then heard it close without me touching it.

 

[Studboy]

Make sure that the subvalves are opening/closing correctly also. You can check by taking out the side covers on the subvalves and turning the powervalve arm, if they go in and out you are OK there. Maybe you should just pull the head off, then you can really see if all of the valves are opening and closing correctly. You will be able to reuse the o-rings on the head.

 

[SpectraSVT]

I tried the bike today with the jetting it had last week and it ran absolutley horrible. Had no power whatsoever. It wouldn't idle...revved really high so I took the carb out and and put in 48 pilot (richer) and the bike died and lost compression. I can move the kick starter with my hand. I'm in the process of taking the bike apart now. Very pissed off right now!

 

[pro2k]

Dude, sorry to hear about your problems. Let us know what you find! Very interested......

 

[SpectraSVT]

Powervalve is not functioning properly. It was working when I sent it out to Eric and now its not. The new plating on my cylinder and the piston are wasted. $450 down the drain. Hopefully they have some kind of guarantee on they're work.

 

[Rich Rohrich]

Like I told you in the other thread. Give Eric a call on Sunday morning and explain it to him. He'll take it from there.

 

[GatorNutz]

I'm interested in the end result...

 

[SpectraSVT]

Thats quite a bit different that what you originally posted...lol. I will definitely post again when its done. Eric just received it yesterday.