[av]

We're waiting on speedy20 for the ride report on his 03 that he did the avNow mod on...

[av]

I contacted Doug Dubach and he's willing to try out the avNow mod and give us his opinions, here is his reply to me:

Subject: Re: avNow mod, please try it, you'll be surprised!
Date: Wed, 19 Feb 2003 21:30:56 -0800
From: "Dubach Racing Development" <dubachracing@sbcglobal.net>
To: "Alan Vinh" <avinh@syntek-usa.com>
References: 1

Alan,
I don't have the old style carb. The new 450F carb has the rear as part of the casting. I will try to find a carb and send it. I am going out of town for a week so I will do something when I get back.
Thanks
Doug

I pointed him to this thread - it will be interesting to get his opinions once he gets some seat time. Maybe they can dyno it too :D we'll see what will become of this when he gets back in town...

[YZFE]

Hi everyone,

I rode earlier today with the James now / Av now / Efi now mod :D
Two weeks ago I did The James now mod. I rode with the mod in one of our natural terrain tracks (wet sandy terrain). The bike was coming out of one of the third gear turns with the front wheel in the air much more then before the mod. The mod worked, but I was glad I did not pay 90 bucks for this !!

Today I rode with the James now / Av now / Efi now mod which is the James now mod with another plate half way below it (plates located similar to the one in the denniskirk online catalog.

Well, today I again rode in the sandy terrain around my house but not in the track as it was too flooded (very heavy rains in the last days). Now the mod is really working !!! The terrain is very wet sand covered with grass in many places where traction is unbelievable !!! Holy cow the bike was wheeling everywhere :lol: The power that used to really come on in the upper mid range is now coming on much sooner and is really great in third gear turns for example and sandy jumps.

Next week I will check the mod in the rocks.

By the way , the lower plate unlike the middle plate has to be flush with the rubber manifold. I had to turn the mixture screw quarter of a turn leaner.

Thanks James and Av for the ideas and instructions!

[vhoomaha]

I finally got to test the "J/A NOW" mod for the second time properly and i was extrteemly satisfied with some minor adjustments.

I did the AV Mod two weeks ago and doing a 6 hour trail ride my bike would splutter and spit while doing climbs in first/second gear
with the throttle 1/4 to fully open, i didnt enjoy it very much and top end felt choked - my friend also rode it and said it was too rich!
So half way through the ride i took out the plates and she was back to normal (boy was i happy)! but with the mod done i did feel a
nice improvement off bottom, but she would still bog when i whacked it from closed to fully open in neutral!

So..... i thought before i post anything let me give the MOD another try!

Today i did a 5 hour trail ride with only one plate in ( the lower one) which sits at 1/3 height in the venturi. I also disconnected
the sky blue wire. Now in neutral/idling i can whack it from fully closed to fully open and she will just SCREAM!!!! from idle to rev limiter - Bog gone!
Now she's still gutsy from the bottom and still gives good top end! I am really impressed and very satisfied with this setup at the moment
and wont be changing it!

One thing i do find in doing this mod is that my exhaust doesnt burn as clean any more (used to be lightish grey) , its a dark grey now with more residue than usuall.
After reving her, her revs hang high for a couple of seconds before returning back to normal idle speed! The mod causing greater velocity
air flow seems to richen her theoretically but isnt hanging revs a lean condition?

BTW my plates are 1.5mm thick aluminium and is placed 0.5mm from the carb slide! the plate has been shaped to give a snug fit
to the carb throat wall and doesnt allow air to bypass.

Jusy curious, having both 1.5mm plates (3mm) in would that have reduced the intake enough to choke the top end?

I definitely feel she is too rich now so i have reduced my air/fuel screw to 1 1/4 turns! I havent changed any other jetting settings .

Just i hope i dont melt anything!

02 yz250f ( Stock jetting)

[speedy20]

Okay I finally got going and missed a day of riding cause i had that darn slide thing in upsidedown. Well I fixed that and am fixin to go rip. I started with plates that were 1.28mm(.050) thick and was scared of to much metal in the way also. After I had them fully installed I knocked them out and started over using .65mm. They look much better. Could the choked feeling come from too much fuel? I have to wonder.

[av]

You guys pretty much had the same conclusions as I did - much improved bottom through mid, but it ran a little rich with slight bogs (on my bike). I can't get out to test the jetting right now, but I bet turning in the mixture screw and perhaps lowering the needle and/or using a smaller pilot jet will clean things up (do only one thing at a time, start with mixture screw, then pilot jet, then needle) - the main jet should be OK. I think most of us tend to jet on the rich side thinking that the bigger the jets, the more fuel/power you get - I believe that this is incorrect thinking, you NEED to be just SLIGHTLY rich bordering lean to get your best throttle response and power. I believe being too rich actually causes you to LOSE some ponies since the engine can't burn up all the fuel hence it won't run cleanly (i.e. bogs) and therefore it's not running optimally.

Having other people trying this mod really helps pave the way for others to figure out the jetting needed for the new air velocity, extra fuel and of course the earlier hit and new improved bottom & mid :D this is way cool that others have confirmed the bottom & mid gain, now we just have to straighten out the jetting and we're golden - I can't wait to test her some more :D

[av]

One thing i do find in doing this mod is that my exhaust doesnt burn as clean any more (used to be lightish grey) , its a dark grey now with more residue than usuall.

You're still running a little rich and it is not burning all of the fuel up - i.e. residue. Dark grey is a richer condition vs. light grey being more towards the lean side, but if it revs fine and doesn't bog anywhere - I'd leave it alone (rather be richer than leaner). If it has slight bogs, you might want to adjust the mixture screw clockwise, and/or use a smaller pilot jet and/or lower your needle one notch.

isnt hanging revs a lean condition?

I think this might be the case only if there is a leak in the boot(s) causing uneven pressure or more air - the fact that your idle comes down means you're OK, otherwise it will stay high with a leak or it would be intermittent high/low idling kind of situation - check your plug to be sure though...

Jusy curious, having both 1.5mm plates (3mm) in would that have reduced the intake enough to choke the top end?

Can you hit your rev limiter? I don't think this really matters for the 250Fs since the venturi is already larger than the carb's throat (same venturi used in the 426Fs, although the thinner the plates the better without being too flimsy - ~1mm should be good if you had a choice). The 4xxFs may not even matter since they don't rev as high as the 250Fs - but if you can stay pinned on a 4xxF bike, you should be a pro because those engines are incredibly strong at WOT! :shocked:

I definitely feel she is too rich now so i have reduced my air/fuel screw to 1 1/4 turns! I havent changed any other jetting settings.

The mixture screw effect is ONLY for 0 to 1/4 throttle (it has little effects beyond that), the needle affects 1/8 to 7/8 with 1/2 throttle being most affected by the needle. The main jet kicks in from 3/8 to WOT, with the most effect in the upper RPM from 3/4 throttle on - see the engine tuning section in the back of your manual. You need to adjust the all of the circuits appropriately to have a clean running bike, not just the mixture screw.

Just i hope i dont melt anything!

Even if your idle circuit (0 to 1/4) is lean due to your leaning out the mixture screw, you're most likely "normally" running in the mid to upper mid most of the time so you would still be fine if those circuits are not lean.

It doesn't sound like you're running lean anyway - check the plug to be sure (although your exhaust pipe indicates a slightly rich condition). If the tip and/or electrode of the spark plug is melting, then you're too lean, but then you would have noticed that with the throttle response (i.e. it would have hesitated, coughed, backfired etc.). Sounds like you're bogging which is a rich condition...

[vhoomaha]

AV
Thanks for tieing up those loose ends for me - all is much clearer now!
My bike is still filthy, so i can only check the plug once i have her cleaned up!

Thanks for your comprehensive reply, VERY MUCH APPRECIATED!!! ;)

Marc

[av]

For those who are interested, the original avNow version 1.0 had the plates at 1/3 & 2/3 spacing. I created the avNow version 1.1 with 1/2 & 1/4 spacing over the weekend using SUnruh's venturi (along with his "unshrouding the MAJ & PAJ" mod he did to this venturi). 03 owners will have to do similar work to their carbs if they want the avNow mod - here is the link (see how I created version 1.1):

http://home.earthlink.net/~avinh3/motorcycles/wr250f/avNow.html

SUnruh - as per our e-mail, I'll try to test version 1.1 around my neighborhood this weekend to compare the 2 versions and send it back to you before I go on vacation next week - not sure if I'll have time though, if I don't have time this weekend, I'll just send it back to you for testing against the original PowerNow that you already have...

BTW - I started my bike over the weekend for the first time with its YZF e-cam and I liked how it revved quicker along with my new found low/mid power - woohooo! :D The stock mixture screw setting was at 2 1/4 turns out, I had it reset to 2 turns out and it started up in something like 6 kicks (the carb must have been empty and I haven't started it in 3 weeks). It was 60oF out and the jetting seemed fine - once the bike warmed up, it revved like a 2 stroke - pretty clean jetting I thought, I didn't noticed any bogs or hickups and it pulled like a mad bull! :D :cool:

[SUnruh]

alan,
COOL pics!
i can't wait to hear how it tests out on your bike.
my "chop" job is not the best and is probably overkill compared to how it is done on the PowerNow. maybe that channel needs some epoxy (about 75% of its length) filled in and smoothed into the radius. can't wait to hear how it goes.

[mikeolichney]

Jeez, this post goes on forever, and I didn't read it all. I did visit the website for Powernow and read the explanation. I have another idea you might try, its kind of obvious, so I apologize if someone already had it. Anyway, if you made the powernow plate an airfoil (wing) you could get even more "signal" out of the flow. It would need to be the opposite of an airplane wing, so that the long flow path is the bottom of the wing. For those of you with technical backgrounds, Bernoulli's equation says faster fluid velocities will result in lower pressures. A wing works because the air must take a longer path accross the top of a wing, resulting in lower pressure on the wing top and therefore net lift on the wing.

I am taking "signal" to mean the pressure drop in the carb that sucks fuel out of the jets. So the upside-down wing would result in greater pressure drop on the jet side and hence more "signal" to pull fuel in.

My take on the 4 stroke "bog" or poor throttle response is this: When you whip a 4S throttle open as fast as possible on the stand, it will die. The mixture becomes very lean because the fuel density is much greater than air density, so the sudden acceleration in flow pulls in proportionally much more air than fuel. Once the fuel gets accellerated up to speed the mixture becomes right and the lean problem goes away. Whacking the throttle open is like towing a large weight on a spring, the weight (fuel) will eventually catch up to the tow vehicle (air), but it takes a few moments.

This is what the accelerator pump tries to compensate for, but I don't think it does a perfect job. There are alot of possible throttle cases to cover, and its a pretty simple device. I think the only way one can accurately assure that the fuel gets into the airstream in the proper ratio under different airflow accelerations is to use fuel injection.

Anyway, the upside-down airfoil might be worth a try. I don't have time, I need to do my taxes.

[YZFE]

What is the the channel for ?

[SUnruh]

yzfe,

What is the the channel for ?



do you mean the original or my mod?

the original is a seperate "tube" if you will, that brings in air from the air box directly to the PAJ and MAJ. on the PowerNow, they close this off and instead open a 3/8" gap right infront of them that is feed from the main intake track.

my 3 brain cells got together and came to the conclusion that unshrouding the PAJ and MAJ could be a GOOD thing. so i just took a hacksaw blade and cut the top part of the tube out. so now the PAJ and MAJ have complete access to all air flow. i think a better way would be to epoxy the far end shut, and cut a simple notch near the paj/maj and then epoxy the end of the tube. however, i didn't have a good idea how to make the semi-circular cut that would be perpendicular to the way the tube runs. i don't have very steady hands and a dremel tends to wander on me. so, i did what i knew i could do and cut the whole darn thing.

[Scaryfast]

I completed the jamesnow mod with one plate on my '01 YZ250F over the weekend and I was very pleased. I experienced the same "snap" and better low to mid revving as others. I made no jetting changes.

One note: I found it unnecessary to have the "T" or little tabs on the aluminum plate at the air box boot end of the venturi. I can see from the latest pictures that the cuts are made at the very end of the venturi for those "T" tabs to slide in a be flush with the end of the venturi to allow proper fit of the air box boot. However, with the tongue at the other end which extends into the 37 mm carb at 12 mm, the plate is held in to place with the shoulders (outlined in black marker in the photos) that are even with the end of the venturi being bolted on the carb. So, this step cut resting on the carb collar will stop the plate from sliding any farther into the carb thus not allowing the tongue to hit the throttle slide. Then, if a step cut is done at the opposite side as well with a smaller tongue extending in to the air boot, these steps which will be flush with the end of the venturi and rest on the inside collar of the air boot will inhibit any rearward movement of the plate. So, you do not have to do the tabs and cut slots for them in the venturi. Just have step cuts at both ends of the venturi, the body of the aluminum plate measuring the exact length of the venturi its self. My tongue on the carb side is 12 mm and on the air box side it is 6 mm. I don't have any pictures. I hope this is helpful.

[YZFE]

SUnruh, yes, I mean in your mod.
Did the channel by itself change anything in the bikes powerband ? If you haven't checked it yet, why do you think the open channel should be an improvement over the original setup ?

Thanks.

[av]

One note: I found it unnecessary to have the "T" or little tabs on the aluminum plate at the air box boot end of the venturi. I can see from the latest pictures that the cuts are made at the very end of the venturi for those "T" tabs to slide in a be flush with the end of the venturi to allow proper fit of the air box boot. However, with the tongue at the other end which extends into the 37 mm carb at 12 mm, the plate is held in to place with the shoulders (outlined in black marker in the photos) that are even with the end of the venturi being bolted on the carb. So, this step cut resting on the carb collar will stop the plate from sliding any farther into the carb thus not allowing the tongue to hit the throttle slide. Then, if a step cut is done at the opposite side as well with a smaller tongue extending in to the air boot, these steps which will be flush with the end of the venturi and rest on the inside collar of the air boot will inhibit any rearward movement of the plate. So, you do not have to do the tabs and cut slots for them in the venturi. Just have step cuts at both ends of the venturi, the body of the aluminum plate measuring the exact length of the venturi its self. My tongue on the carb side is 12 mm and on the air box side it is 6 mm. I don't have any pictures. I hope this is helpful.

Trying to understand what you've done:

1) I take it that you used grooves to keep the plate from rotating(?)
2) You used the step cut and the carb's throat to keep the plate from moving forward
3) You used the step cut and the air box's "collar" to keep the plate from moving backward

For item 2 above, this may not work for older 4xxFs because although they share the same venturi piece as the 250Fs, their carbs throats' diameter is 2mm larger than the 250Fs hence the step may not be there - I don't know for sure since I haven't seen the throat of the 4xxF's carb.

I hope you have used glue to keep the plate in place and also from rattling. If you have used glue, items 1 through 3 are really moot points, since the glue will not let it move anywhere (from my experience so far).

What I've find easiest to do is instead of grooves, cut slits on the air box side (like I've done for my versions 1.1 & 1.2 - no more grooves). The tabs will anchor the plates while the glue will keep the plates aligned and in place. The plastic used for the venturi piece is so hard (and slippery) that it is very difficult to keep the grooves parallel to each other if you're using multiple plates for the avNow - so doing away with the grooves is a good thing... :cool:

Hint: When cutting the slits, start each side off by itself, then once both sides are scored, then you can cut both sides of the venturi's lip simultaneously - only about 4mm to 5mm deep, stop just as you enter the groove/ring on the venturi's air box side.

FYI: I measured my 250F carb's throat and it is actually ~15mm deep, so eventhough the original PowerNow uses 12mm for its tongue, you can get closer to the slide. I've actually used 14mm tongues for my version 1.2.

Reminder again: If you use glue such as epoxy, make sure it is solvent and heat resistant since everytime I take my venturi piece out, it is wet with fuel :shocked: Makes me wonder if I'm running too rich, yet my bike seems to rev fine (more on this in my next post). This is the glue that I use. (http://www.loctiteproducts.com/Loctite_Products/detail.asp?catid=11&subid=49&plid=157)

[av]

Test results for avNow versions 1.1 and 1.2

On Sunday it was cloudy and 65oF. I installed version 1.1 (plates at 1/4 & 1/2 spacing). Blipped the throttle twice and 4 kicks later it started. Rode it around the neighborhood and noticed a slightly better punch down low to mid (versus version 1.0 where the plates are at 1/3 and 2/3 spacing) but the throttle wasn't as smooth as version 1.0 going from low to WOT - in neutral where this is most noticeable, the revving was slightly slower than version 1.0 with slight bogs going from low through WOT (i.e. whacking the throttle).

I installed version 1.2 (plates at 1/4, 1/2 & 3/4 spacing), rode around the neighborhood and noticed the same punch as version 1.1 but with a smoother transition to WOT. I had it WOT in 4th gear up a straight road and suddenly, bog, bog, bog, dead engine! :shocked: Oh sh*t! Did I break my engine?! %$&@#! Kick, kick, kick... nothing! I was 0.7 miles from home and had to push that 250 lbs bike up and down hills back home. I tried to bump starting it going down hill and nothing! :crazy: I was hoping that nothing broke in the engine and that the fuel system was just too rich and caused my spark plug to foul (i.e. from all that bogging at WOT). Finally made it back to the garage (all that pushing was very tiring!) - got my spare spark plug, my smaller jets (175MJ and 38PJ), my tools and I was ready to work on leaning out the carb. Put my stool down, sat down and doh! :mad: I had turned my fuel off when I installed version 1.2 - I'm sure many of you have been there done that! :blush: She started right up once I give her the needed juice - what a relief! :D Took it around the neighborhood again with no incident. Tested the revving in neutral and noticed that it revved better than version 1.1 but not quite as fast and as cleanly as version 1.0. I think dropping the needle one clip position will clean up the throttle nicely, it seems slightly rich through the mid - I didn't have time to fix the jetting (another day's project).

Conclusions:

This is my setup:
- YZF timing
- FMF PowerBomb head pipe
- Stock WR silencer with Vortip
- 12T CS sprocket (stock was 13T) with 52T rear sprocket
- 178MJ (stock was 175 IIRC) and stock 40PJ IIRC
- Fuel screw at 2 turns out (stock was 2 1/4)
- Needle clip at stock position 4 IIRC

Version 1.0: Revved the fastest & smoothest with the above jetting setup but has slightly less punch down low to mid (i.e. the difference was hardly noticeable). Easiest version to make.

Version 1.1: Better punch down low to mid versus version 1.0 but throttle transition from low to WOT was not as fast or as smooth as version 1.0 - slight bogs probably due to the change in the induced are pressure right at 1/2 throttle.

Version 1.2: Similar punch as version 1.1 down low to mid but smoother transition from low to WOT compared to version 1.1. Didn't rev as fast as version 1.0 but I think this is due to the richer mid throttle condition of the induced air - dropping the needle one clip position should clean this up. Hardest version to make (tripple plates).

From the limited testing that I've done (and I stress limited) - I would use either version 1.0 or 1.2 - if I had to decide, for my riding style, I would pick version 1.2. Version 1.0 may be better suited for people riding mostly at WOT (less plates to limit the air flow) yet still have that low end pull when needed. It would be nice to dyno these things - maybe some day...

[av]

I dyno tested the avNow vs. the stock venturi this past weekend on my WR250F with the FMF PB SX and stock silencer uncorked. I asked the guy (he races and tunes street race bikes with the DynoJet machine so he knows his stuff) about the HP and why it isn't as high as I've seen (i.e. in the upper 20s and low 30s) - he said don't believe the hyped up numbers, look at the curves :excuseme:

So I'm looking at the curves for where the torque and HP differences are and it's hard to see because the printout lines are so small it was hard to pick up with my scanner but if you look closely, you can see the red line as stock, blue line as avNow version 1.2 and the black line (which I had to pencil in because the green wasn't showing) is avNow version 1.0. You can see obvious gains in HP and torque for the avNow version 1.2 over stock in the low to mid RPM (i.e. 4K to 7K RPM), yet version 1.0 (with shorter tongues at 12mm vs. 14mm for version 1.2) shows a strange curve (worst than stock?) - it is pretty weird looking at the graph when I know I can feel the difference down low to mid with version 1.0 and 1.2.

The fuel mixture graph also shows that I was running way too rich in the middle and slightly rich in the upper RPM - he told me if the jetting is better, i.e. leaner, my bike would be registering better curves. He told me to drop my needle one to two clip positions (I dropped it one clip position to #2) and perhaps lower my main jet from 178 to 175 if it's still running too rich after dropping the needle. I dropped the needle and it seemed fine with me so I'd rather run it slightly rich than lean. I asked him about the fuel mixture screw and the PJ and he said those are mostly for the idle circuit and my bike is idling really well already so I should leave that circuit alone.

So you can see there is a very slight loss in HP up top (0.3 HP & 0.2 ft-lb) but a larger gain down low to mid as suspected from my "seat of the pants" feel (almost 1 HP & 2 ft-lbs). Keep in mind that with the original PowerNow, I had no feeling of the power gain down low, yet it did wonders on the tracks/trails with stall resistance and pulling higher gears so with the avNow, I'm expecting the same characteristics as the PowerNow but I've also gained torque, HP and I'm doing wheelies much easier :cool: :D :thumbsup: Can't wait to go riding which will be very soon now... :D :D

Here is the dyno graph (http://home.earthlink.net/~avinh3/motorcycles/wr250f/misc/dyno_uncorked_small_with_text.jpg).

[av]

First real test on the track at RocketRaceway (http://www.rocketraceway.com/). The track condition was pretty ideal with some tacky/muddy areas but overall pretty dry and sunny ~70oF.

The avNow version 1.2 ran flawlessly, no stalls all day, idled great, had to lug my bike around in first & second while escorting the lady around the track a few times. When I did get away by myself, it revved great through and out of the berms, plenty of power on hills and wheelies where easy - can't complain :cool:

[av]

Here are pictures of the avNow version 1.2 after a season of hard riding through trails, mud, water, tracks, etc. - 320+ miles or so, that's pretty good for a weekend rider like me :lol:

avNow version 1.2 with subframe raised (http://www.imagestation.com/picture/sraid99/p793c5118ef07ae4b6f496f3165f91c6a/f9fdf41a.jpg)
avNow version 1.2 close up 1 (http://www.imagestation.com/picture/sraid99/p83bcc55647cb0e790ba05be8ef3bcdd0/f9fdf4bc.jpg)
avNow version 1.2 close up 2 (http://www.imagestation.com/picture/sraid99/pd2cf0ab55ede58a227d94ac058fe0554/f9fdf46e.jpg)

The glue and plates held up well! :cool: :thumbsup:

[Taewa]

Permission is forbidden to the last two links. Is there an update?

[wrooster]

the correct link is in his sig.

e.g.,
http://mysite.verizon.net/avinh/motorcycles/wr250f/avNow.html



jim aka the wrooster
'01 wr250f

[e.myers]

It lives!!!!!!!!

[yamaha_george]

Hi,
since the plates are supposed to help the venturii effect how come you have not curved the plate at the slide end so that the effect is maximised?

[wrooster]

yeah Av, what's up with that? :excuseme:

didn't this show up when you did the wind tunnel testing?
you could of even found it with CAD/FEA hydrosimulation.

jim aka the wrooster
'01 wr250f

ps: :goofy:

[pkley]

Anyone else using the avNow 1.2?

[av]

since the plates are supposed to help the venturii effect how come you have not curved the plate at the slide end so that the effect is maximised?




didn't this show up when you did the wind tunnel testing?
you could of even found it with CAD/FEA hydrosimulation.



I should have hired both of you to come up with the best fit/design and paid you the same amount I got for putting it all together - zilch! :lol: :lol:

George, way at the beginning of the post (if you had read the whole thing we had discussed this somewhere in there), the original PowerNow design didn't have a perfect fit either (see link to pictures of it in my sig), so I didn't worry about the perfect fit either. BTW, the newer design for 03, 04 & 05 isn't a perfect fit inside the venturi either, their gaps are bigger than my plates have next to the side, i.e. their plate is still too short IMO, and they use the same piece for a 250F and/or 450F so you KNOW the fit is NOT exact. Anyway, the bulk of the air velocity/pressure that is changed from the plate(s) is what counts, not the minor leaks on the side and front of the plates. :excuseme:

[thump353]

what about trying to make them the shape of an airplane wing (i know we are working with a small area) when doing the dual avNOW with the arched part of the wing on the top. do you think that it would speed the air up and give you almost some sort of slight supercharged effect :thinking:

[homernukem]

I think your kidding your self on thinking it will help on the dyno. Unless you can limit the throttle to only open 1/3 or 2/3 the way then I believe it will help. I plan on doing a similar mod soon.

[SUnruh]

thanks for bringing up a post 4 years old!