2000 YZ250 Setup (flywheel weights, porting etc.)

[Sphinx]

I am getting back into riding, after a ten year hiatus, and am setting up my 2000 YZ 250 as an all around play bike, for lack of a better term. I grew up riding 2-strokes in the open desert and am now riding in the New England woods, the occasional MX track (practice track and don't race) and have been toying with doing some Hare Scrambles, but I am not at that skill level yet. Needless to say I am out of my element and getting used to a totally different riding experience.

When I first got my bike a few months ago I thought it flew and it does, but now that I am getting used to the power I am finding the low end kinda flat and then the power really hits hard. I am putting a FMF Gnarly pipe on it, because the original stock pipe is beat up and an FMF Q silencer, because of noise reasons.

So my question is what type of porting would you recomend and would a flywheel weight work well with it? Also what are your thoughts about the Boyesen RAD valves?

Currently the bike is stock, with a new piston and rings (about 20 hours on them now), with stock jetting and I am running a BR7ES plug, instead of the BR8EG. My riding style is conservative and I tend to prefer to short shift. I am not looking to make this bike something it isn't, but would like to make the power more predictable/smoother.

 

[bclapham]

sphinx: if your are looking for lowend power, this porting is the way to go, best bag for the buck, i ride mainly MX.

http://www.dirtrider.net/forums3/showthread.php?threadid=60221

a couple of people have ridden it and like it a lot, and they were both top end screamer guys

most of the people i have talked to say the v-force reeds are good, ive got some but havent tried them yet

i might try a very light flywheel at some point also, just to take the edge off the wheel spin and impove hook up.

i strongly suggest you put the stock br8eg plug back in and mess with the jetting to get it running right.

good luck

BC

 

[Sphinx]

Why do you suggest going back to the stock plug? I ride at WOT very rarely and never for a prolonged amount of time.

With the stock plug it would load up when running at low rpm and take a few seconds to clear out, when I whacked the throttle open. The BR7ES runs really well, but will listen to any thoughts/experience.

Thanks.

 

[bclapham]

it is probably not running correct with the 8 plug because of poor jetting, and swapping the hotter plug to give acceptable performance is not the best way of doing things since you are only treating the symtoms and not the cause of the problem. From the information i have learned in other threads, running the wrong plug in this situation only increases the chances of very expensive engine damage, espcially as you get faster and do more riding, or even if the weather makes a sudden change. Surely a few dollars spent on jets is worth it to ensure both excellent performance and peace of mind?

maybe before you spend lots of money on engine tuning, you should especially look into your correct jetting, since here is where a very significant increase in performance can be had very easily....it doesnt matter how much performance mods you make, they are worth nothing unless the bike is jetted properly.

 

[Studboy]

bclapham, I often run a BR7 plug for trail riding or woods in my 250. Unless you run sustained WOT the 7 should work fine. MXTuner (on off-road.com) suggests this a lot. You are right though, Sphinx the main reason it isn't crisp is probably because of your jetting.

 

[Sphinx]

I see your point about jetting properly. What do you suggest changing first? Everything is stock except for the Twin Air filter, the Jet needle clip is in the second position (one leaner than stock) and I just packed with the silencer.

With the stock BR8EG plug, running Sunoco 94 with BelRay H1R synthetic at 40:1, it was running rich (poor throttle response and plug is wet)and when I nailed the throttle all the way open it would gurgle for 5 - 10 seconds and then clear out and run better for a few minutes and then load up again. Also the air screw was 1.5 turns out and it would idle fine. Where would you suggest starting? Main jet, pilot jet, jet needle or power jet? Also I am about 100 ft above sea level.

I am looking at the 2001 specs and find it interesting that the main jet is one size richer and the Jet Needle is two sizes leaner.

Any input would be great, thanks.

 

[Studboy]

I would start with the pilot jet. Then work your way to the needle and main. There are good jetting guides everywhere if you search for them...or at www.ericgorr.com under tech articles. Your jetting definately needs to be cleaned up, it should not load up like that REGARDLESS what plug you have in there. But running the 7 plug will not hurt anything, I use it to keep things up to temp at lower RPMs. The only place you should need the 8 is at the sand dunes or at the MX track or anywhere where you run extended high RPMs. I believe that Marcusgunby runs a 8 heat range plug in his high performance 125, the stock plug is a 9 or 10! He has had no ill effects due to this that I am aware of. But the root of the problem is still your jetting. May I also suggest using Mobil 1 MX2T premix, many people here have had good luck using that oil and it is less expensive than Bel-Ray and readily available at Autozone.
Good Luck, -Studboy-

 

[Bill Purcell]

I've been running the 7 plug based on the recommendation of several people (including Eric Gore). However, I seem to have the jetting figured out (with race gas) and I don't notice any difference. The biggest thing is that if you ride slow like me :) your plug will stay cleaner.

 

[Rich Rohrich]

Originally posted by Studboy
But running the 7 plug will not hurt anything,

Assuming that can be really expensive when you guess wrong.

You can read the heat of the plug fairly easily once you get the jetting sorted out. No one ever hurt an engine running too cold a plug, but the trails and tracks of America are littered with engine parts from folks who ran too hot a plug.

Read the plug and you'll know if a 7 is safe for your use. There are a number of threads here on DRN that go into great detail on how to determine proper heat range. Here's just one of the many ==>> Click Here

 

[Sphinx]

The more I think about it, the more I think it is the main jet that is too rich, because I only get the gurgling at full throttle and it has always started and idled well.

 

[Glitch]

The main jet is for when the bike gets up into the high rpm, not for getting there. I would try leaner on pilot or needle. Attempt with air screw first. Also, if you ride around for awhile at fairly low rpm, I think you should pull in the clutch and rev the bike some to clean it out before you start riding aggressively. IMO though.

 

[Studboy]

Originally posted by Glitch
The main jet is for when the bike gets up into the high rpm, not for getting there.

Jetting is determined by throttle opening position, not RPM.

 

[Sphinx]

I get the gurgling at full throttle with the RPMs in the middle. Main jet or needle?

 

[marcusgunby]

Needle.

 

[bclapham]

Originally posted by marcusgunby
Needle.

marcus: why dont you just get straight to the point! :thumb:

get it, needle, point! hehehehehehehehehehehe! :silly: :confused: :yeehaw:

 

[marcusgunby]

Bruce i should have read it better-full throttle is main jet but i suspect the needle is still partly the problem in Sphinx's case.Could even be a rich pilot and its taking till mid rpms to clear its throat.

 

[Studboy]

I agree with Marcus, I would start with the Pilot then move to the Needle, then the Main. They are all probably rich.

 

[Sphinx]

Thanks for the help guys. As soon as it warms up here, I certainly have some tinkering to do.

 

[bclapham]

did nobody like my joke? at least i thought it was funny!:)

sphinx: i assume you will have the stock pilot jet (i think its a 50). I tried the 48 which was better and the 45 which was better still, maybe pick up a couple of similar pilots from the shop and go from there.

 

[Sphinx]

The pilot is the stock #50.

I thought your joke was funny.

 

[bclapham]

:thumb:

buy both jets and go have some fun!

 

[whyz]

Jason Raines has 3 bolt-on parts, a 9 ounce flywheel weight,an FMF Gnarly pipe and an FMF T-2 Shorty silencer on his 02YZ250.
His motor is stock off the shelf besides the bolt-ons.
This combo smoothes out the blast of the machine,creating a tractor-like volcano of juice that lets him carry a higher gear and chug,
rather than clutch it an spin.
I read this in The best and worst awards of DirtBike mag. Oct.issue.

 

[Sphinx]

I saw that too. I think he also has a Boyesen RAD valve. I have always liked the GNCC bikes.

 

[bclapham]

to see for myself, i went and ran a BR7ES plug this saturday.

it didnt run right with the 45 pilot and still spooged (only a bit)

went to the 48 pilot and it still didnt run right, it ran better but was pinging coming out of corners, only in the pilot circuit and i couldnt get rid of it even with the air screw.

all of this was with a richer needle clip also.

the BR8 is going back in!

the best i have had the bike run on pump gas is 48p 2nd NE3J 175 main

 

[Studboy]

The BR7 was obviously too hot for your application. I never reccomended the BR7 as a band-aid fix for poor jetting, it is only to be used in the proper application, such as a hotter heat range plug for lower-RPM's and trail riding.