How far out is too far on pilot screw?

Hi all

Got an 02 CRF450, got a JD kit for carb and have been playing round with tune... red needle at 5th clip, 180 main but the pilot is at 3 full turns out to get rid of popping on deceleration... is 3 turns out ok to do or should i do it some other way ???



Sounds like you may need to up a size on the pilot jet. More than 3 turns out on the screw is usually not recommended.

3 full turns out is the most u will want to go.

# turns is too far, you should never be more than 2.5 trns. Go up a size in pilot, probably will be at about 1.25 ~ 1.75 turns.

a slight pop on decel is normal.turning the fuel screw out or going to a bigger pilot jet just to "cure" popping just makes it rcih.

yea it was a lot more than a slight pop, it was more like pop, pop, pop crackle, pop pop etc..... either way thanks for the input guys. went from a #45 pilot to a #50 and 1.5 turns out and is perfect !!! Thanks again :-)


50 is way too big.

you have other issues.

Suspect you have a major air leak at the head pipe, it is letting air in which mixes with hot gas that sipons thru the idle circut at closed throttle (but does not burn as throttle is blocking air).

Fix the head pipe, If you want silence your going to need a pipe a couple feet longer.

42 pilot, no more that 2.5 turns on the screw and acknowledge that its not the carb

Im new to all this 4 stroke stuff so i am still learning and making a few mistakes yea...went back and had another go at the jetting as i screwed pilot in and it didnt change the idle at all, so out came the #50 and put a #48 in. Moved screw into 1 1/8 turn out and idle fell away so i moved out 1/2 a turn and it seems to be working spot on, is this the correct procedure? I dont know if it should be using a smaller jet than this but it seems to be working for me....


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.

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