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50 pilot in an 07? UPDATE

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i recently picked up an 07 yz250f. i think i read somewhere that stock pilot is a 42. it has a 48 in it now and still seems to be lean on bottom. carb is clean. the fuel screw is already 4 turns out. it pops and cracks at steady throttle, at least till i reach past 1/4 throttle. gets worse as i turn it in. should i bump it up to a 50 or could there be something else that would cause it? seems like 50 would be pretty big for it or is that normal?  elevation here ranges from about 1000 to 2600 feet. temps are in the 70's

 

UPDATE!!! just changed the pilot to a 42. screw is at 2 3/4 turns out to get best idle. man this thing is finicky. 1/8 turn in either direction and the idle starts dropping. still have the popping at constant throttle (below 1/4 throttle), probably due to the needle. off idle bog is gone after doing the o ring mod. havent taken it on a real ride yet. just up and down the road.

Edited by ridinredneck

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Pilot and fuel screw are for idle ONLY. Anything over a 45 is to rich. At 7,000 feet, I'd think youd be running a 40 or a 38.

 

Off of idle, is the straight diameter of the needle (changed by swapping out the needle) and above that (half throttle) is the taper, adjusted by the clip or changing the needle length).

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Pilot and fuel screw are for idle ONLY. Anything over a 45 is to rich. At 7,000 feet, I'd think youd be running a 40 or a 38.

 

Off of idle, is the straight diameter of the needle (changed by swapping out the needle) and above that (half throttle) is the taper, adjusted by the clip or changing the needle length).

i have to disagree. the needle comes in to play at around 1/4 throttle. the pilots job is from idle to about 1/4 throttle and the mixture screw helps from idle to almost 1/8 throttle

Edited by ridinredneck

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i have to disagree. the needle comes in to play at around 1/4 throttle. the pilots job is from idle to about 1/4 throttle and the mixture screw helps from idle to almost 1/8 throttle

 

I was not sufficiently clear and you mis-read.

 

A fuel screw is a fine adjustment for the pilot circuit. It is a seperate feed from the pilot. 2.5 turns on the fuel screw equates to about one pilot jet size.

 

The fuel screw/pilot jet operate all the time. As the throttle opens, the needle comes onto play. At first, it is mostly the pilot ciurcuit but the percentage of total fuel being added transitions to the needle as the slide opens and the air volume under it increases.

 

FCRTuningguide.jpg

 

Off idle is the straight diameter of the needle. That is about 1/16th throttle To change this, you must use a different needle. The last letter in the code changes this. Higher in the alphabet, the leaner.

 

Once you get to 1/.2 throttle, it is the needle taper,(and length) The point on the taper is changed (in fine adjustments) by the clip position and in rough adjustments, by the needle length.

 

Carb circuits are all transitional.You adjust the idle first, as the fuel from the pilot circuit affects the fuel from the straight diamter, which inturn affects the fuel the taper which inturn affects the fuel from the needle lenght/clip poision and finally the main jet.

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IMO, if you need a 50PJ to get it to run, you've got problems somewhere else. In all the years of jetting being discussed on this site, no one ever required a 50 PJ. IMO, something is wrong with the wr guy who is using a 48 PJ even though it's a BB.

In all these years of discussing which PJ to use, 38-45 Pj were the choices.

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Pilot and fuel screw are for idle ONLY. Anything over a 45 is to rich. At 7,000 feet, I'd think youd be running a 40 or a 38.

 

Off of idle, is the straight diameter of the needle (changed by swapping out the needle) and above that (half throttle) is the taper, adjusted by the clip or changing the needle length).

The 42 PJ worked fine with the stock engine.  But after a rebuild with a 269 kit and stage one cams it was a little too lean so I went to a 45.  Had to replace the carb with one from a newer bike.  Carefully cleaned it, still a little too lean to went to a 48.  

 

Maybe something is wrong.  I saw on a sportbike forum how the best way to clean a carb is to use an ultrasonic cleaner with Pine Sol.  Something to try this winter.  

Edited by flyandride

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A big bore should require leaner jetting, not richer. It is taking bigger gulps, this in turn creates a higher vacuum at the carb, which sucks in more fuel, hence leaner jetting needed. The is whight the bigger the engine, the smaller the jets. Look at the main of a YZ450 compared to a YZ250.

 

Nearly every YZ250 I have worked on uses a 42 pilot except in extreme cold. The YZ is one of those bikes that feels like it is on the cusp of needing a 45 however when you try and fine adjust the fuel screw, the bike tells you it is too rich.

 

You have something wrong with your carb.

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IMO, if you need a 50PJ to get it to run, you've got problems somewhere else. In all the years of jetting being discussed on this site, no one ever required a 50 PJ. IMO, something is wrong with the wr guy who is using a 48 PJ even though it's a BB.

In all these years of discussing which PJ to use, 38-45 Pj were the choices.

 

I would also add that on any big bores I ever did you usually stayed close to the same or ended up jetting down.

Edited by Charlie755

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Needle position is only for above 1/4 throttle.

 

You need to start at the beginning (idle) and work your way up. Do not just 'do something', do it for a reason. Identify the exact problem area (not just 'feels like 1/4 throttle', know EXACTLY). Otherwise, you will never get it right. Popping and such at steady throttle is 99.99% of the time a rich condition. But first find out why you are so rich on the pilot.

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Needle position is only for above 1/4 throttle.

 

You need to start at the beginning (idle) and work your way up. Do not just 'do something', do it for a reason. Identify the exact problem area (not just 'feels like 1/4 throttle', know EXACTLY). Otherwise, you will never get it right. Popping and such at steady throttle is 99.99% of the time a rich condition. But first find out why you are so rich on the pilot.

i have identified the problem area. here is what i know for a fact. it has very little power on bottom until i hit the 1/4 throttle mark, then it screams. starts easy, idles great. has a bog to it if i try to take off fast or on an incline. (have to work the clutch). at a constant speed (but higher rpms like going down the highway) it crackles and pops through the exhaust, but only below 1/4 throttle. it has the stock pipe on it. when i got the bike it already had the 48 pilot in it. it had a horrible bog to it, it would die if i cracked the throttle very fast. played with the screw and got it to where it doesn't die. but the above problem remains. i have checked for air leaks with carb cleaner and it has a new air filter in it. the carb is clean. 

 

you said it sounds like a rich problem. so i will pick up a couple smaller pilot jets and see how that affects idle and starting. i will also check to see where the needle is set. i WILL get it figured out (with help of course lol). the reason i started this thread is because a 48 pilot seemed awful big to me. thanks to all for the help thus far

Edited by ridinredneck

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Aog has nothing to do with the pilot, it is the AP. You must get the base jetting right (for steady throttle, under load) correct prior to attempting to resolve a bog. It sounds to me like the typical attempt at jetting where the person has no idea what to do. First, they turn the fuel screw because it is 'right there' and it goes down hill from there.

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i'm gonna get the jetting right first then see if it still has the bog to it. i just came off a long run on 2-strokes and have been jetting them for some time now. i had forgotten about the AP on 4-strokes till a couple days ago. i am also gonna check the ap squirt and get that right too. but correct jetting is first. 

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when you're doing your jetting, forget about the bog until last. roll on the throttle during testing. the bog will be cured by adjustments in the AP circuit.

FYI, the OEM needle for the 07 wasn't well like by most of us. We found that the 08 or 09 needle worked much better. A JD needle worked well also.

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yea jetting is gonna be first. and thanks for the heads up on the needle. i will look in to getting a different one if this one dont suit me.

my experience with the 07 needle was I couldn't lean it out enough. I was on 2nd clip (another TT'er was on 1st) and while the bike ran pretty well while in the needle part of the throttle, when you turned throttle WFO, the MJ was lean. I'd switch to fatter MJ and the needle portion would be too fat.

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