honda 450r jetting and ap mod 07 questions

Ok SO I bought an 07 awhile back in terrable shape so i striped it ALL THE WAY DOWN cleaned and replaced everything SO 700 $LATER in cosmetic and maitnance parts, I am in the last steps putting it back together , I read all the ap mod threads i could find , bought a 90 leak jet , and finally took the carb apart yesterday , what I found for jetting was a 180 main, a pilot jet 42 and another jet 72 and leak jet 50 ,and the air screw at 2 turns ,i did not ride the bike to any extent before i toar it down , but it did pop alot when wicking the throttle on decel So my question is the bike only has a carbon white bros full pipe which has a short pipe and a long muffler with a large bigger then silver dollar size exit, and a uni air filter with the screen still in it, does this jetting sound good? and how do the two other jets 42/72 work together? and finally the diaphram was a short one already ,and i found there wasen't a reason to oring or wire the drum together because it followed the stroke from closed to open staying in contact the whole way,

Any guidence you can give will be much appreicated

165 main in the summer, 168 in the winter, and a 45 pilot at 2.0 turns out on the fuel screw.

That will help with the decel popping, and be a close enough starting point that you'll probably never change it.

thank you , wonder why the guy had a 180 in it? what do the two jets do together the pilot and that 72jet in there how do they work together?

You may find even the 165 is too big. Keep in mind, the main is only for WOT. People put stupid big jets in often the main because they always think richer is better. It is an easy part to swap and even though it is way large, they rarely ever run WOT and therefore do not notice. They just think the bike runs better, they never actually test. Bizarre, isn't it?

The 72 jet is the starter jet, it is fine.

You may regret having changed the #50 leak jet to a 90 unless all your riding is high speed desert running. If you run the woods, you will want that 50 to make the AP give you the fuel you need for low rpm throttle opening.

Read the following to set the fuel screw crorrectly and ensure the pilot you have in is best. Too small a pilot makes the bike prone to stall, increases decel pops. Too large a pilot makes hot starts more difficult.

Fuel Screw/Pilot Jet

Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.

Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.

*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***

Turn the screw in until the idle becomes rough or the bike stalls.

if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.

If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.

Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.

If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.

If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.

If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.

As far as decel pops, once you have the pilot, fuel screw set for a perfect idle, you can check the exhaust for leaks. Hld a towel over the end and listen for hissing. If the decel pops are a big proble, go back to the stock exhaust.

Race bike+race exhaust=excessive decel popping. Mainly because no one in a race ever coasts.

thank you for the reply i know that took a while to type up , i don't do any desert riding all small-med mx tracks ,so i'' keep the 50 and swap it back in so i can get a back to back comparison , because the bike had pretty bad decel pop and the pipe turned bright orange near the head , real quik at warm up i think i'll start with a 45 pilot and a 165 main and tune from there i put in a finger adjustable fuel screw also to make it easier to tune

thanks again

Decel pop has nothing to do with the leak jet. Glowing thin wall header is normal for a bike sitting in the garage idling. It needs air flow to keep it cool

I knew about the leak jet, it was just part of what everyone recomended as part of the ap mod , what i came to understand is there were differences from 02-08 that got blended to gether in the ap mod threads ? i havent took the time to understand what affect it had excactly , i just assumed bigger jet there meant more fuel available to the squirt , im assuming from your post it leaks more fuel back out to the fuel bowl leaving less gas for the squirt?, seemed kinda weird to me that a 50 comes in it , and i was jumping jets almost double couldn't see kiehn engineers being that far off , if im understanding this right ,i'll just throw the 50 back in , when i change the main jet, have to look and see if i can find one in my jets i know i have a 45 i know the pipe wasnt leaking so with a 42 now and just over two turns out , i think ican assume a 45 will help

thanks again

There are three types of FCRs when talking OEM Honda. Old slant style, from 2000 and prior, standard FCR-MX up through 2007 (I think) and from 07 to now push linkage instead of pull FCR-MX. This difference means no stiffer spring/oring or wiring of the linkage needed.

Now, most small bore bike do use a leak jet, many large bore do not however... the goal with leak jet selection is to always run the biggest you can without a bog. A bog is basically dependent on two things. Quantity of fuel delivered (leak jet and/or diaphragm rivet length) and AP timing. Starting with the timing carefully set exactly per OEM specs, then you ride and fine tune the timing. Then use progressively larger leak jets till the bog returns. See if further timing adjustments improves things, if not, go back one size in leak jet. The smaller the leak jet, the more fuel the system delivers. A leak jet 'leaks' fuel away from the AP so a bigger jet means more leaking.

OEM leak size is based on the type of rider who is supposed to be buying the bike. Meaning these are state of the art race bikes and the rider is a near pro level MXer. Which 99.99% of the buyers are not. The rest of the jetting is based on the bike being at sea level, 65 degrees F, 30 inches of mercury, 50% humidity.

Your last sentence was misleading. You talk of the 50 leak jet but then transition to talking about (I hope) pilots.

thanks again , carbs coming back off and going back to the 50 leakjet, 45 pilot , and 165 main as a start.

i read back threw my last post i confused myself ,i was thinking faster then i type :thumbsup:

thanks for clearing up how the leakjet works

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now