[mdtoney]

After reading the AP mod how-to I opened up my carb to verify the jetting and see what mods have been done.

I have a '07 450X with opened air box, smog hoses removed, backfire screen removed, and full Yosh exhaust. I ride mostly woods and occasional desert terrain near sea level, in temps 45-75.

Jetting:
Main-165
Pilot-45
Leak-70
Starter-70
Slow air-100

Needle: JD red, clip is 4th from the top

Fuel screw: 1 3/4 turns out

When I bought the bike I did the AP link o-ring mod and added a Boyesen Quick Shot 2 cover.

The diaphram rivet has NOT been shortened yet.

The bike starts easy enough, idles good, and runs cleanly once it warms up. To be fair, I've never ridden a FI dirt bike, so I don't know how much better throttle response 'could' be, but I don't have any noticable issues.

When I twist the throttle, there is no gap between the AP link lever and AP set screw at WOT. With the o-ring mod, the lever and screw always move together.

I've seen that a 70 leak jet is recommended as well as the shorter diaphragm rivet, or a complete updated AP kit http://www.crfsonly.com/catalog/product ... ts_id/3932

Do I need the longer rod and shorter diaphragm rivet in this kit? And is the updated AP cover better than the QS2 cover?

If there is a noticable difference in throttle response I'll shorten the rivet and install the 70 leak - but I'm not sure if I would need the complete kit - I don't want to waste my money if it's not needed.

Thanks for the help guys! Sorry this was so long....

[crfsonly]

it would be worth installing the AP kit we offer as preventative maintenance if for no other reason. the AP diaphragm are known to deteriorate over time so doing this will provide you a fresh diaphragm. letting them go to the point they start to break away you risk getting bits of rubber in your AP circuit.

the update will help the function of the AP both in the improved diaphragm and the check valve being moved to the AP. Your QS2 will not longer work if unless it is the version that has the check valve in the cover.

ken

[mdtoney]

I ordered the 50 leak jet and the AP kit.

As I understand it, the check valve needs to be removed because the new cover has a check valve built in. I'm not sure what the check valve actually does, but I noticed that I've been running the built-in check valve, plus the one in the QS2 cover.
I'm really confused now - I thought this wasn't supposed to work??

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[crfsonly]

fuel gets from the float bowl to the AP via a circuit that uses a check valve to prevent fuel from flowing out of the AP back into the float bowl. initially this check valve was in the float bowl. now it is in the AP cover reducing the distance and thereby increasing the responsiveness of the AP.

ken

[mdtoney]

Ken, thanks for the explanation on what the check valve does!

The check valve in the updated cover is in a different location than the check valve in the QS2 cover.
Is that why I can no longer use the QS2 cover? It sucks I spent $90 on it and have to throw it out!

[crfsonly]

you can continue to use the QS2 with the update kit. however, if you do use it do NOT remove the check valve in the float bowl. install all but the new AP cover and continue to use your QS2. you will still benefit from the updated diaphragm, new spring and o-ring/d-rings.

ken

[mdtoney]

Cool. Thanks for all the help Ken!!

[mdtoney]

After changing the leak from 70 to 50 and doing the AP mod, is it necessary to re-jet??? I've ridden it twice since the changes and don't notice any positive changes.
The bike ran really clean before the changes and didn't need either of these mods, (I was just hoping a good-running bike might run even better!), but now there is a low-end bog when I hit the throttle quickly. I've tried to dial it out with the fuel screw but it doesn't do anything.
The bike still idles fine and still runs good (once in a while it's a little harder to start), but now there's a low-end bog that I never noticed before.

Any ideas what I did wrong?

[crfsonly]

did you have a check valve in the float bowl? if so, what it removed? what AP cover are you using the QS or the updated Honda cover? what is your fuel screw set at? are you sure the fuel screw has just one of each of the washer, spring and o-ring?

[mdtoney]

I stayed with the same setup that I had before changing the leak jet and doing the AP mod - the check valve in the bowl and the one in the QS2 cover.
Right now I'm not sure what the fuel screw is set at, I changed it so much on my last ride trying to remove the bog. Before the mods it was 1 3/4 turns out - it's probably pretty close to that now. I'll check tonight.

I took the fuel screw out (as well as all other jets) when I did the mods and cleaned everything. There is only 1 washer, spring, o-ring in there.

The bog is only at low rpm, if I hit the throttle quickly. The throttle response seems fine otherwise.

[crfsonly]

have verified you have a long and strong AP squirt? you'll need to look into the rear of the carb to see this squirt. it's not unheard of for the nozzle to become clogged or partially clogged.

[mdtoney]

I have not verified the AP squirt. Is there a good video or write-up explaining what to look for and the proper way to adjust it, if it's off? I watched one video that was confusing and poor video quality, so it didn't help at all. Plus, the bike ran good before the mods and the mods I did were both supposed to further improve throttle response, so I didn't even bother checking the squirt... I probably need to go back in there.

[crfsonly]

i'm not a fan personally of the the leak jet adjustments. the AP update kit has a shorter pin diaphragm (good) and a replacement spring, washers and the cover. all good and would not have negatively affected your AP function if installed correctly.

AP squirt is just the fuel squirting from the AP nozzle in the throat of the carb. it's a visual test. so, all you need to do is be able to look into the back of the carb and then whack the throttle it engage the AP.

[crazybrother]

Here's a good video of the AP squirt.
http://www.youtube.com/watch?v=ool_jiy4kxQ

And another one:
http://www.youtube.com/watch?v=ZbzBbLYeATw

I personally would buy the kit and replace your QS2 and remove the check valve and spring from the float bowl. Then put in a #50 leak jet and you should be good to go as long as everything else is clean...
I see your bike is an '07 therefore you don't need the O-Ring MOD.
The check valve is right next to the Leak Jet, just push the ball,spring and plug right out the bottom with a small tipped screwdriver or similar tool.

Here is the best tutorial on how to rebuild a Kehin Carb.

http://www.dirtrider.com/features/proti ... b_rebuild/
Read the top portion, then click on the first picture, then scroll through them all and reading the description on each picture will tell you all you need to know.

[mdtoney]

Thanks for the video link! I'll check it out and tear into it the carb this weekend.

I've already swapped the 70 leak for a 50 and installed the AP kit with the shorter pin. However, I did not use the new AP cover, I used my old QS2 cover. When I have it apart, I'll remove the check valve in the bowl and use the new AP cover.

I checked the fuel screw last night, it's 2 turns out.