[Scoots_36]

I've never seen a carb for a 03 YZ450f but it sounds like it is similar to the CRF carb, with an aluminum bell. If it is, the guys on the CRF board have been doing the power now mod for a while. There are a couple threads but the best one is titled "you think we've got it bad.....". It has pictures and rough dimensions. The basic concept is to cut two grooves in the carb bell for the dogears of the power now to fit in and have a press fit into the throat of the carb. Hope this helps.

[matt_rohr]

After enjoying the benifits I realized from the power nows I purchased for my wr280f and ktm520. I removed the chokes on a 22 and 24mm carbs I run on my moded xr120 I made a template from a business card then I taped it on a piece of sheat metal. Then you shape it with about a 32nd wider on the side area, next you sharpen it in this area. Next take a tiny file and cut a bunch of groves to create teeth on the side. Then start trying to carefully push it in very straight. It will cut a grove as you do this. Just keep sharpening and narrowing until it fits in very tight. If the carb. is a round slide make the leading edge just miss the slide, shaped around it.If its not perfectly flat or has a little twist, just reach in with some needle nose pliers and straighten. When your finished it will be in there so tight, combined with the sharp teeth it will never come loose. Even if one of these plates came loose its too large from every dimension to ever get through the carb. anyway. Put a little red loctite on the blade area and your finished. good luck, Matt

[Junior_Vet]

These are all great ideas. I'll see what I can figure out. I just brought my bike home today. Had a little boot in the parking lot and it seems real smooth. I was looking for the 1/4 throttle miss but it didn't appear. I'm keeping my fingers crossed.

Thanks for the ideas.

[av]

1) This one is pretty obvious - make the plates and weld/glue them directly into the 03 carb's venturi making sure they can not go forward or backward.

Junior_Vet - I think this may be your easiest option. To add to the above mod (option #1), cut slits into the carb's venturi on the air box side about 1 or 2 mm deep to keep the plates in place, the boot will go way beyond the slits to seal properly (so no worries). Once you have the slits cut into the carb's venturi, you can make the plates with its safety tabs that will slide right into the slits. Glue the plates to the slits and side walls of the venturi and you're done.

WARNING - I don't know who's reading this thread, but kids at home don't try to weld anything to your carb's venturi unless you have your carb COMPLETELY FREE OF GAS :shocked: This is pretty obvious, but you never know who might try this mod and don't think things through - doh! :shocked:

Well what do you know... I went to read the "You think we've got it bad" thread in the Red forum (http://www.thumpertalk.com/bike/ubbthreads/showflat.php?Cat=&Board=UBB29&Number=286103&page=&view=&sb=&o=&vc=1), about a quarter of the way down, "ride_red" did exactly what I've just described above with his plate, he included a nice picture of the plate...

[Junior_Vet]

I saw that post too. The picture really made it easier to understand.

Thanks for the suggestions av.

[kkannracing]

The F is a responsive bike of the showroom floor...but I am anxious to see how it pulls out of a corner .... like a tight corner, in third gear, suspension pressed, good hookup, starting about1/3 throttle.......don't forget to point your toe av. :D

[av]

Shhhhhhhhhhh! Those of you still tuning in, keep it quiet! I need to sell my original PowerNow so don't let the cat out of the bag just yet... :D The rest of you guys with the original PowerNow, do the avNow and you'll want to get rid of the original PowerNow too... :blush:

Physics prevails! All I can say is wow! :shocked: WOW!! WOW!!! :D :D :D The air induction really works! :D

I've been running the following setup for the last 6 months on my 02 WR250F:

- 178 main jet, the rest is stock jetting
- 12T/52T sprocket ratio
- PowerNow
- FMF PowerBomb SX head pipe
- WR stock silencer and Vortip
- WR timing

As you can tell, my power concentration is for bottom end to mid pull using the sprocket ratio, the PowerNow and the FMF SX head pipe.

On Saturday it was partly cloudy and around 30oF (-1oC). I blipped my throttle 3 times to prime the engine and it started with 1 good kick (I last started it 2 weeks ago). I warmed the bike up, then took it around the neighborhood streets - I wanted to get a good feel of what my throttle response is like doing various things such as WOT, whacking the throttle, etc. with the above setup using the original PowerNow venturi piece. So after a going around for 5-10 minutes I have some baseline "feel" of my bike again.

Right after I stopped the bike, I rode my TTR-125L around to get its juice flowing for about 5-10 minutes while my WR250F is cooling off. I then took out the original PowerNow venturi piece and noticed that it was damp with gas :shocked: I didn't realize that gas went backwards so make sure that if you use glue that the glue is solvent resistant - I supposed the air was cold and perhaps it backfired a little as I decelerate (although I didn't noticed too much backfire happening :confused:). I then tried to install the avNow and noticed that my tapered tongues didn't fit right because the carb's throat is not tapered but it was smaller than the venturi hence the reason why the original PowerNow has a step like cut to its tongue (see the original PowerNow in the background of this picture (http://home.earthlink.net/~avinh3/motorcycles/wr250f/misc/DSC00211.JPG)). You'll have to cut the top avNow plate like this (http://home.earthlink.net/~avinh3/motorcycles/wr250f/misc/DSC00213.JPG) and the bottom avPlate like this (http://home.earthlink.net/~avinh3/motorcycles/wr250f/misc/DSC00214.JPG) - notice the revised step cut in order for it to fit into the carb's throat properly (the 4xxF carb's throat is larger and probably won't need the step cut). I blipped the throttle a few times to make sure the slider was not stuck anywhere in its full range of motion - of course this pumped gas into the carb and caused a flood like condition.

After the installation of the avNow, I first kicked it a few times without the choke to clear it out a bit, then finally a few more kicks with the choke and she started right up. After a minute, I took the choke off and took her out for a spin doing all of the tests that I did with the original PowerNow earlier on the same streets (e.g. WOT, whacking the throttle, etc.). As you PowerNow owners know, it is hard to tell a power gain with the PowerNow and what you end up noticing is the following:

1) Better snap from low to mid throttle, crisper throttle response
2) Resists stalling better at low RPM
3) Starts better (cold & hot), the hot start button may not be needed anymore
4) You can ride/pull a taller gear better in low RPM
5) Even after a spill (i.e. possible flood situation), the starting is easier

I didn't expect too much of a difference but boy was I pleasantly surprised! :D :D :D I just couldn't stop smiling while I was testing (I'm still smiling just thinking of it). My hookup was pretty good since I'm on pavement (i.e. didn't slip) and I'm mostly on straights (i.e. no berms etc. obviously). The meat is brought down low to mid just like I wanted! It felt like I've gained 10cc, a couple of ponies and a hand full of ft-lbs! I kept saying to myself wow! WOW!! WOW!!! I have never felt this BIG a difference in the bottom end pull from any of my mods. Although the 250F isn't known for a strong bottom end, this mod really beefed it up! AND I'M RUNNING WITH A FREAKIN' VORTIP AND THE STOCK WR CAN! I can't stop smiling :D :D My front wheel kept coming off the ground (2nd & 3rd) without my having to do anything with my weight or pulling on the handle bar etc. (the original PowerNow didn't do this) - power wheelies - wow! :shocked:

Bottom to mid was where the most noticeable difference was (as intended/designed), mid to top end seemed similar but smoother like the power band shifted down and hit much sooner - just think when I install the 03 YZF e-cam and get the YZ timing too! :shocked: whoooohoooo! :D

I can't wait to test this thing out on the tracks in the berms, pulling taller gears, lugging her real slowly etc. - I've got a really bad ITCH for riding with my new found bottom end yet it's too cold to go riding... :(

Jetting - I did noticed that with the same unchanged settings to my carb, the throttle seemed even smoother than before with better snap/response and it idled a little faster (less work from better induced air flow?) so I had to lower the idle screw a bit and everything else seemed fine. I didn't get a chance to check my plug so I'm hoping that it won't require any jetting changes since everything seemed to run pretty well but to be sure I'll have to pull the plug to make sure it's not running too lean/hot - if anything, it seemed to run a little richer :confused: anyway, I didn't have enough time to mess with the jetting...

I AIN'T GOING BACK TO THE POWERNOW - I have my original PowerNow on sale on the parts forum if anyone wants it (it DOES work well but the avNow is BETTER :D) - keep it quiet about this avNow mod will ya? I gotta get rid of my old PowerNow piece... ;)

Wait until the factory boys get a hold of this secret/mod! Shhhhhhh, don't let the boys in red know... :D

You guys with the original PowerNows, can you try the avNow in your setup and report back your finding (gains, losses, differences, jetting changes, etc.)? I'm curious as to what the rest of the PowerNow users find in their comparisons with the avNow - especially you guys in warmer weather and can still ride, I'm curious with you jetting gurus (SUnruh if you're reading?) if anything had to be changed to the jetting...

Whooohooo, yeeeha, yippeee :D :D :D

[vhoomaha]

AV
I have an idea that you may want to experiment with!

Without getting into the nitty gritty of how the "***NOW" works, the essential idea
is to get air flowing in a more linear pattern by using the plate, which then also increases
the air flow velocity due to the smaller venturi.

IDEA:
Now if the edge of the plate on the air box side was not cut square but had and edge
that was shaped like the inner edge of an Australian/Aboriginal "Boomerang" or the profile of
an egg, would that not increase more air into the carb since it will also pull air from the top of the plate
- but then you would need to calculate or experiment how far this concave edge will need to
be cut back into the plate without disturbing the airs linear flow.

I could post a picture of the drawing i have in mind but dont know how exactly to post on TT - all i know is
that i need to have the picture on the internet somewhere first ! of which i dont have anywhere on the internet
to put pictures!

Vhoom

[Dirt_Surfer]

av, you better hurry and apply for a Patent! :D


idled a little faster (less work from better induced air flow?)


Your increased idle speed comes from the hole that passes through the intake bell. The Power Now doesn't have this passage which supplies air directly to the main air jet (when the slide is closed). That's my theory since I had to increase my idle speed when I installed a Power Now.

[NemadjiMan]

av - I appreciate the fact that you did a whole bunch of work and it sounds like you ended up with a pretty good mod. I don't mean to throw cold water on your efforts but I want to point something out. You put in two plates, one lower than the center of the venturi and one higher. It is my guess that the lower plate is the one that actually made your bike more responsive off the bottom. The higher plate is so high and far away from the carb's jets that it probably isn't doing much of a "turbulence smoothing" job. I know that the only way to prove this out would be to actually try the "av now" with and without the upper plate. I guess that the next guy that tries your mod could make the top plate temporarily removeable to see if it really makes any difference. Less turbulence over the jets is better, but so is less stuff in the airstream. Just a thought.

[Dirt_Surfer]

av,
I had similar thoughts to what NemadjiMan said, that the "additional" plate may be ignored by the jets. I wonder if World Power Racing had done any R&D with multiple plates. Anyhow, you deserve another gold star! :D

[av]

My 2 plates concept was to induce air into the carb using smaller openings into the carb's throat which also increases the torque/power - as for smoothing out the air turbulence, that was the theory behind the original inventor of the PowerNow venturi (it may or may not be valid I can't/won't debate that theory since I have no way of proving it either way). I can prove the velocity theory via my many examples already...

The second plate was to keep the mid range of the throttle also induced with more air by the same concept (i.e. a smaller opening) thereby increasing the hit in the middle. The smaller plate definitely boost the 0 to 1/3 throttle response but power seems to carry over into the middle hit which is where the power wheelies were happening (i.e. my throttle was not at 1/3 or less - more like 1/2 to 3/4). The concept of using smaller openings to induce air (in my mind - not to smooth out air) for more power seems to work from my initial tests on the street...

It would be nice if others can try it out and report back. These venturi pieces are only $6.96 listed (according to Yamaha of Troy (http://216.37.204.205/Yamaha_OEM/YamahaDB.asp?Type=13&A=209&B=12), part #4), so if you want your original venturi piece back (i.e. the "JOINT, AIR FILTER 1") it didn't cost you much to try the avNow mod out. We're going to try this mod on my friends YZ250F and YZ426F along with testing the original venturi to see the difference. These tests won't be for a while since we have to order the venturi pieces and then make the avNow mod to them, then wait for good weather for our ride tests on real tracks. I wish someone who can ride in Ca or wherever there is decent weather would give it a go and report back...

[vhoomaha]

AV / anyone - any feedback on the suggestion of an egg profiled plate i posted earlier???

[NemadjiMan]

av - maybe I'll putz with this myself. It certainly is cheap enough. It'll be a while before I can try anything out 'cause it's 5 below outside again today. So, have you decided how much you are going to charge us for the royalty fee??

[av]

It'll be a while before I can try anything out 'cause it's 5 below outside again today.

I feel for you - we're in the same situation with the cold just not AS COLD as MN. Burrr... :(

So, have you decided how much you are going to charge us for the royalty fee??

Free for all - no patents ;) if it works out for my fellow TT members that would be great since TT has helped me with many other mods and questions - I'm glad I was daring enough to try it first, you never know unless you try, sometimes it's a bust sometimes you find gold and this is definitely on the golden side... :D

[av]

vhoomaha - I saw your idea but don't quite understand how that would increase the induction :confused: if you have some theories/facts that you can bring to the table for discussion we might be able to think this through before making a prototype...

The plates are there to increase the flow, by opening up the area/plate, you might defeat the purpose - you mentioned testing with various cuts of the concavity but how do you figure that part out? I guess you would just try various cuts and see what works best.

The "seat of the pant" tests are very hard to quantify on paper - but the difference between the PowerNow and the avNow, power wise, was very noticeable hence I was shocked! :D I did NOT noticed a definite power gain with the PowerNow but CAN tell it pulled better on the tracks out of corners, using higher gears, starting, stall resistance, etc. I bet the avNow power gain would show up on the dyno chart - anyone with access to the dyno willing to run the tests? I.e. stock vs. PowerNow/JamesNow vs. avNow? That would be easy to do by taking a stock venturi (part number BTW is 5JG-1440F-01-00 for the 250F and 426F) and cutting 3 sets of grooves in it (the middle set is for the JamesNow and the other 2 sets are for the avNow). How about keeping all 3 plates in there (avNow+ :D)?

I have only one venturi piece and the avNow mod worked out well - if you still have your venturi, why don't you try different cuts with the plates and let us know if your idea has any merits. Just don't glue down the plates until you're sure of the shape that you want...

[av]

FYI - I read in the Feb 03 issue of "Dirt Bike" among all of their recommended mods (I don't remember the pages), but for the PowerNow mod they indicated that for 2 strokes almost all of them had to be jetted leaner once the PowerNow was in place.

I didn't have to rejet my 250F using the PowerNow, but in testing the avNow, I did noticed that it seemed richer even though everything ran well/better - I noticed some slight bogging (i.e. a rich condition) which was strange since it was pretty cold out. I'm thinking that the extra air velocity going into the carb/engine, giving it its new found power is also carrying extra fuel hence the richer condition, so if you try this mod out, keep an eye out for jetting changes (i.e. a richer condition)... I haven't had too much time to mess with the jetting since it's so cold out, but I'll definitely fine tune it ASAP.

I started it again 2 days ago in 32oF and it acted a little differently when I primed it 3 times, choked it and kicked (usually this would crank her right up), but this time it wanted to start but didn't at first and I could see some fuel on the ground. After a few tries, I figured she was flooded, so I pulled the decomp lever in, no choke, WOT and kicked it 20 times to clear the cylinder. I then choked the carb, no throttle or priming, and she started right up - again it seemed like a rich condition and acted differently from the PowerNow mod. I think I'll adjust the fuel screw accordingly when I get around to testing it more. Once started, she ran pretty well with the head pipe glowing and all, I didn't ride it around the neighborhood since it was late and didn't want the noise police on my case... :smirk:

[speedy20]

Hey AV keep typing. I made one for my 03, just slotted carb and left ears on dividers. I think they are about 14 mm apart. I hope it's as good as you say! :D One thought though, will two plates cost anything at WOT. They take up some space but if they are straight with the flow they should be all right??? Please post any jetting changes....Thanks...

Also here is some GOOD epoxy 3M Scotch-Weld 2216B/A. This stuff won't crack, chip or flake. Has very good flex. Used it on my helecopter....

[MADDOG419]

av: Good post, new ideas are always COOL. Need more of them, on how to increse VELOCITY some good reading at
http://mototuneusa.com
You have to sign up to read past & future issues
THANKS TO ALL :cool:

[Junior_Vet]

speedy,
How deep did you cut the slots in the carb?

I'm a little nervous about cutting into my carb.

How did you modify the plate shape to fit the carb instead of the bell housing?

[yamahabud]

Cool where can I get it :D?

[vhoomaha]

AV, you got an email address i can send a jpg file to?
It's a drawing of the idea i posted earlier!

Marc

[speedy20]

I cut about 4mm is all. The ears on the plates look big enough to me at that depth. And the carb is tapered anyway so if didn't want to cut and just use epoxy it should work. I guess it just for safety to me. The neck on the carb has plenty of meat to go a little deeper and still be strong I guess. I made a plate to divide the carb in half and just kept sanding it smaller off of each side to get it to the desired height. The top and bottom plates don't match as the carb throat change's towards the top. I think I'll use a little epoxy just to make sure they hold still, but they are tight enough they don't move anyway (yet) ;).

[Junior_Vet]

speedy,

Thanks for the description. I like the idea of making it a little big and sanding to slowly approach the right size. I'll give it a try on the weekend and see.

I haven't been able to ride my bike yet (there was no snow the week before I got my bike) so I think I'll make the plates but not mount them for now until I get a feel for the new bike. Otherwise, I may not know how much of a difference that the avNOW and your tips have made. ;)

[av]

speedy20 - Glad someone else has the nerves to try the avNow mod! ;) You should notice a definite gain in low to mid, much sooner power hit and better off idle response (i.e. 0 to 1/3 throttle). If you're like me and probably most of us who can't ride WOT all the time, this is were you'll be running most of the time (i.e. in the low to upper mid). Did you get a chance to ride it around the neighborhood yet? Any reports?

As for top-end, I didn't noticed any changes, it still wind out like nuts and once you get past the second plate, you basically should have the same volume for the air intake as the original venturi. I don't think those thin plates would hamper anything - but I'm curious for those who ride WOT to report any changes. This is a pretty cheap mod to try since the venturi piece is only ~$7 for older models - for 03 models, you'll just have to remove the plates if you don't like them (i.e. reversible).

As for jetting - I haven't had a good chance to test the mod other than my initial run with some WOW results. I did noticed what seemed like a slightly rich condition with slight bogs so you might have to adjust your mixture screw inwards (i.e. clockwise 1/4 turn or so), as for the mid, if it's rich there, then drop your needle one notch. The main should be the same since you'll be back at using the full venturi's diameter (although you might have to drop the main jet's size too since the induced air might be carrying too much fuel with it). What you basically want is to lean out the jetting for best throttle response, then adjust so that you are just slightly rich and that would be your best setup (according to our local tuner guy).

Good luck, let us know about your test rides, especially if you are able to get on real tracks and trails.

[TexLaBo]

Okay..now that this conversation is really going, let me throw this at you gurus.

Now, I believe the power now works because of the increased velocity theory, but I don't discount the lack of turbulance as well. It could be they both play a part in this product working. However what about this:

If this works so well on the intake side, but perhaps a combination of these on BOTH sides of the carb...continuing the effect all the way to the cylinder? Or peraps for those of you believing strictly in the "turbulance" theory...perhaps a verticle plate between the carb and cylinder would help? It wouldnt change anything in terms of throttle openings, but rather keep the air flowing in two channels apart from each other to reduce swirling, with the possibility that the two channels of air would swirl together at the final edge of the plate creating a concentrated charge to the cylinder intake.

Just thought I'd send all you big thinkers back into your laboratories <G>.....but it just might work.....

Tex

[RippinInColorado]

Have you had a chance to run the AvNow solution? Feedback?

Does anyone know if the Dennis Kirk device will fit an 03 YZ450? My carb is a 39mm, but a different model. I don't have the model number with me at the moment; let it at home.

I'd be happy to pay $30 for the commercial unit so I don't have to grind slots in my carb. But only if it fits and is an improvement. Anybody used the Dennis Kirk unit?

[RippinInColorado]

Okay, well, I just noticed on the Dennis Kirk site that the Starting Line device is on the engine side, not the air box side, so it does not do the same "make the carb seem smaller" thing. So I'm not really interested in that.

Not being much of a machinist and not very adventurous with my new blue baby, I'd be interested in buying a PowerNow for my 450 if someone does the AvNow (or wants to unload their PowerNow for whatever reason) and wants to sell it.

[yamaha250f]

I'd be happy to pay $30 for the commercial unit so I don't have to grind slots in my carb



You DONT grind slots in the carb. You can buy another intake bell for 5 bucks incase you mess up or do not like how it turns out.

[RippinInColorado]

The 03 doesn't have a separate boot between the air box and the carb. The air box clamps straight on to the carb. The PowerNow folks made a little insert that looks like the 2 stroke models - kind of a cone shaped thing with the wing in it.

To do a homemade JamesNow or AvNow, you have to grind/file slots in the bell of the carb. Or just glue and hope it doesn't move.

Has anyone actually done an '03? Any results to report? Anyone done and AvNow on an '03?