Popping and running lean

well my bike is slightly popping and running lean

can really tell when letting off in say 3rd gear it will pop and what not..

i was told to adjust the air-fuel screw but just curious if i should loosen the screw and move it out or if i have to move it in and tighten it??

thank you for the response and should i do 1 full turn or 1/2 turn or what would be sufficient to start with

thanks in adavance

bike is 04 yz450f

You want to richen it up some.

Turn it out (left) to richen it up. Usually when the temp is cooler. 1st thing of a morning.

Turn it in (right) to lean it out. Usually when the temp has risen. Later in the morning or day.

Make your changes in small increments. 1/8" to 1/4" turns to find the sweet spot.

Do this everytime you ride and you'll be alot happier with how it runs.

Slight popping is relatively normal, my bike will also do it occasionally when letting off the throttle in 3rd gear. The fuel screw (don't call it an air-fuel screw on these four strokes) is adjusted as follows:

Make sure the bike is fully warmed up (don't just let it idle, it's better if you have already been riding it) 1) shut the bike off, and use a very short screwdriver to turn the screw in until it LIGHTLY seats. 2) Now unscrew the fuel screw, while keeping track of how many turns you are backing out, and stop at 2 full turns. this is basically a default setting. 3) Start the bike up , and use the idle adjustment knob to make a higher than normal idle ( I think 1900 rpm is recommended, but most of us don't have a digital inductive TACH, so just give it a higher than normal idle) 4) begin turning the fuel screw in until the bike starts to stumble, run rough and almost quit.(by turning the fuel screw in, you are leaning out the carb) stop turning the fuel screw in, and then slowly turn the screw out till you get to maximum rpm. As soon as you get to maximum rpm, STOP; this should put you pretty close to proper mixture. What you want to acheive is this maximum rpm setting with a crisp sounding exhaust. What I mean by this, is that when you are at this setting (maximum rpm) the exhaust sound should sound crisp, when you hit the throttle. If the exhaust sounds muffled slightly, or dull sounding than you have unscrewed the fuel screw just a tad to far out (too rich) and need to turn in maybe an 1/8th or 1/4 of a turn. Just remember to try and acheive the maximum rpm, along with the crispest sounding exhaust note. My bike on a hot, humid day will need to have the screw turned in a little, and than the crispness comes right back to the throttle. Oh by the way, do yourself a favor and get a Zip-Ty fuel screw replacement or another aftermarket fuel screw replacement; using that little screwdriver to do these adjustments is a pain in the rear. It becomes easy with the Zip-Ty or another company's fuel screw replacement.

man i know this sounds bad, but which side is the fuel screw on? by the idle knob side?

Did you check your exhaust for air leaks? If the gaskets are bad it will cause popping too.. Just a thought, thats what was causing mine to pop and bang on the downshift. Adjusting the air/fuel screw did help but it was like putting a band-aid on the problem.

ALso the pilot jet is the smallest jet in the carb. They can clog easily. Clean it out first if this has just kind of started recently.

man i know this sounds bad, but which side is the fuel screw on? by the idle knob side?

It is under the float bowl and unless you have an aftermarket adjustable fuel screw, you will need a small flat screwdriver or just the bit.

well my bike is slightly popping and running lean

can really tell when letting off in say 3rd gear it will pop and what not..

ibike is 04 yz450f

You know these bikes pop and backfire if they are rich too?

You may be rich or lean. Don't rule either possibility out. The rich jetting popping is louder and more obnoxious and the bike doesn't run correctly.

Lean just feels more anemic but it doesn't do all the bucking and coughing that rich jetting gives.

For some reason everyone here likes to give advice that winds up jetting obscenely rich. I have no idea why either. :banghead:

check the clamps on the carb. My old use to do that.

In reality the popping on decel doesnt indicate rich or lean when under acceleration, only that there is not enough fuel when the slide is closed. 2 entirely different problems. A slight amount of popping on decel seems to give better throttle response. It takes patience and the willingness to try different settings.

In reality the popping on decel doesnt indicate rich or lean when under acceleration, only that there is not enough fuel when the slide is closed. 2 entirely different problems. A slight amount of popping on decel seems to give better throttle response. It takes patience and the willingness to try different settings.

Fastest......going to the GMB? :banghead:

right on i found it.... good tip for the screwdriver bit too

You know these bikes pop and backfire if they are rich too?

You may be rich or lean. Don't rule either possibility out. The rich jetting popping is louder and more obnoxious and the bike doesn't run correctly.

Lean just feels more anemic but it doesn't do all the bucking and coughing that rich jetting gives.

For some reason everyone here likes to give advice that winds up jetting obscenely rich. I have no idea why either. :banghead:

Well, and for some reason, some people can't determine where to start first.

OK, then what's his problem?? Where would you start? Fuel screw in or out?

It could be a 1/2 dozen different scenarios but you gotta start somewhere. In his original post, he suspects that it is lean and wanted to know how to adjust his fuel screw for a lean condition.

Well, and for some reason, some people can't determine where to start first.

OK, then what's his problem?? Where would you start? Fuel screw in or out?

It could be a 1/2 dozen different scenarios but you gotta start somewhere. In his original post, he suspects that it is lean and wanted to know how to adjust his fuel screw for a lean condition.

It would be real easy to figure out where to start if everyone would post thier jetting specs in relation to thier riding conditions.

And considering that its isn't real cold anywhere in the country, why would it all of a sudden become 'lean'?

well it has always been a little lean i suspect since i got it...

completely stock bike motor wise and no changes to jetting, exhaust, NOTHING DONE AT ALL

so i was just wondering how to richen it up a bit, i ride in michigan which should be right at sea level or nothing too high above...

thanks for all the answers and suggestions!

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