I don't get the AP trends!

[whenfoxforks-ruled]

05 CRF450R, 168 main,42 pilot,needle 5th from top,mixture at 13/4 out, 40 degrees. Indoor racing is sick with this! It was difficult to jet until I put in a 65 leek jet. I added the jd big o-ring for kicks and I was not happy with the stock setup! The gap is set at 1mm, alot better off idle than 2mm. So there is this ap circuit that shoots a small amount of fuel when the carb comes off idle, #55 (stock) is to rich, flooding my jetting out! One jd kit had a diaphram without the stop nipple, increasing the charge, why? Quickshot, near as I can tell increases the volume of fuel, why? Performance wise has greatly increased throttle response over the stock setup. I see no purpose in chugging fuel into the header and turning pipes blue and belching flames on occasion. Did I miss something, now if I could charge all the fuel these setups offer, say 100lbs then I would not need any jets! (a little exaggerated) No spooge in the header!

 

[Ol'89r]

In my experience with the AP circuit on the 450 carb, it's not how much fuel is sprayed into the carb but when the fuel is sprayed. The slide has to be opened a little bit before the ap sprays the fuel. If the ap sprays before the slide opens it will hurt your throttle response, especially if you are using an aftermarket system that sprays more fuel than stock.

Most of the jets in the carb don't really start to work until the slide opens a little and the atmospheric pressures in the carb change. Only then will the engine accept a direct charge from the ap circuit. If you introduce a charge to the carb before that is is too much, too soon.

 

[whenfoxforks-ruled]

No its not like that, the ap timing is the easy thing to set, 1 mm and go! Why is jd and quickshot hellbent on flooding the carb??? I had to tame the stock leek jet to get it to respond. If I put the 30 leek jet in, the jd diaphram and quickshot, I'm saying why do I need a pilot or main, that is how much fuel it dumps in!!! The entire stroke of the slide is flooded with fuel, not a shot off idle,as is my knowledge of what the ap circuit is supposed to do.

 

[Matt90GT]

first off you are better eyeing the AP timing so that it just missed the carb slide rather than measuring it. Second read this so you understand the relationships of different parts in the AP circuit:

<img src="http://m.bobbitt.home.comcast.net/yz426fm/tech/ap1.jpg">

Once you get the timing down, then you need to set the volume. Which is EASILY done with different leak jets and diaphrams. Most of the time, you just install a different leak jet.

Now before the leakjet was installed in the FCR carb bowls (aka the yz 400f and 426f) you had to tap and drill the carb and add some limiting screws to mimic what you can do with the leak jet. Still the jets are much more precise.

for the AP covers, they are a waste of money. The leaks jets and diaphrams is the correct way to jet the circuit.

 

[whenfoxforks-ruled]

I was pretty much right! Got a note from jd himself, he ducked around what his diaphram was for, but confirmed the quickshot crap!
"The Quick-shot does less than adding a leak jet. Yes, grinding the stem off the diaphragm has a greater effect.
(---And I don't get it either---- but good marketing sells the covers like candy)
I don't sell Quick-shot covers because it's simply taking unknowing people's money.
See- http://www.pbase.com/jdjetting1/image/67912885
And- http://www.pbase.com/jdjetting1/image/27786716
The pump O-ring increases pressure on the diaphragm, which is also a more significant benefit on most bikes." I'll be checking out some of them needles, thanks jd. Before trying to dial in your jetting you have to dial in the leek jet and ap timing, you don't want to be flooding your throttle response off idle with, bad timing or to much raw fuel! I'm betting that properly jetted that them fancy headers would not be turning blue or the pipe glowing yellow! Until someone harnesses burning fuel in the header and getting it to the ground??? Good Luck

 

[sandflyz]

The diapram is so that you can wire your ap link lever to yur timming screw and ensure there is no gap between the two. The diaphram has a shorter stud. Unless you use the diaphram with the shorter length, your throttle linkage may start to bind at wide open throttle. Jd gives you an oring with his kit. This isn't the way to go. You have to wire it to get the full effect. Once it is wired then what happens is your duration increases because because of the shorter rivet length on the diaphram. So. What you do is put in a larger leak jet. Lots of guys are using #90's. I think they are 55 stock. By doing this, you are leaning out the ap circuit as more of the fuel will be returned to your bowl instead of being shot into the motor. The leak jet combined with wiring your linkage makes for some crazzy throttle response. So much so that for 07 Honda revised the linkage to emulate this mod guys have been doing. whenfoxforks-ruled you are only touching the tip of the ice berg. The reason that your bike responds so well is because you put in a leaner leak jet. If you put in the diaphram that jd gave you and dropped in a #90 leak, your throttle reponse would be crazzy. It not only works on Honda's, but any bike with an FCR carb. Which is all of them i think.
For the most part the quick shot is junk. It is only making a bad situation worse in that most of these bikes are rich in the ap cirsuit to begin with. Then guys put on a quick shot and make it worse.
Make sure you ap timming is good, jet the bike properly, then do the mod.

:blah: