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!

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, 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...

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

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??

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...

vhoomaha - I saw your idea but don't quite understand how that would increase the induction 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! 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+ )?

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...

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...

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! 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....

av: Good post, new ideas are always COOL. Need more of them, on how to increse VELOCITY some good reading at
http://mototuneusa.com
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THANKS TO ALL

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?

Cool where can I get it ?

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

Marc

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) .

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.

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.

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

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?

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.

Quote

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.

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?