new guy with old question

[billy the kidd]

first of all hello, this is my first post, i live in northern California, i just bought a new to me 2007 wr 450, i love the bike,,it didn't have many hours on the bike as far as i could tell, i went on a couple short rides on around the house and was impressed with the power, very smooth and strong,since i didn't really know what all was don't to the bike i took it to the local Yamaha shop to have them go through it , adjust the valves ,and give i t a check over to see what had been done to it,,as it turns out the ais is removed, grey wire cut,adjustable fuel jet installed,throttle screw changed,and it has a fmf power core 4 pipe, so to try to get to the point, Friday i loaded the bike up and went to the local ohv area with a buddy and rode about 30 miles through the trails , again worked perfect , no problems i could tell, very strong, and smooth, after i got home i washed the bike as it got dark and then stared it up to put it away , it started coughing and spitting and all of a sudden from an idle if i snap the throttle to wide open it will stumble,,

I went out the next day and loaded it up and took it out to ride with my father, it was doing the same thing after it warmed up (the weather and the bike)it seemed to get alot better,,,,this was the first time i noticed it stumble while ridding it kinda cutting out from idle on a hard acceleration, and doing some popping on decel maybe even a little backfire

so my thoughts are that maybe its a little lean, my only explanation for it not doing this stuff the first couple of rides is that it was about 35 or 40 degrees warmer on the days it ran good than on the days it was popping and stuff,, could it be that i was just on the line of being lean, and the cold dense air made it leaner,,, or do i have something else going on,,,,

i don't know what jets are it it,, i would think with all the other things done to the bike they would have re jetted it , but it came from southern California where it is usually alot warmer , I'm only at 800 ft. but i do get some pretty cool weather,

my last question is how hard is it to change the jet my self , as I'm not usually the kind of person who lets others work on my stuff,,,, thank you for reading this long explanation and i would really appreciate some help,,,

[FORMA MOTO]

Take out the jets and clean them.

Check your hot start plunger: it hangs up and causes random issues.

Adjust your fuel screw ever ride for best results.

[billy the kidd]

do i have to pull the carb off to pull jets? and how do i check the plunger? thanks for the input

[FORMA MOTO]

do i have to pull the carb off to pull jets? and how do i check the plunger? thanks for the input

No, you don't have to remove the carb. It helps to have a friend keep the carb tilted/twisted. while you do jet work.

The plunger issues will be obvious when you remove it. Be careful! The black plastic cap breaks easily! It unscrews, but is flimsy. You can replace it with a zip-tie allow one if you want.

[billy the kidd]

where is the plunger at? i hate to say it but I'm a little ignorant when it comes to newer bikes,, i picture would be awesome if anyone has one thanks

[tribalbc]

Are you sure you didn't get the air filter wet when washing it?

[FORMA MOTO]

where is the plunger at? i hate to say it but I'm a little ignorant when it comes to newer bikes,, i picture would be awesome if anyone has one thanks

See the black thing at the front of the carb? That is where the hot start cable goes in. That black thing screws into the top of the carb, but it gets brittle over time, and no longer screws in correctly. The plunger then get oxidized from exposure, and gets sticky. Heck, even a kinked hotstart cable can drive you nuts chasing down jetting issues.

http://www.motocrossactionmag.com/Media/News/2010_YZ250F%20airbox.jpg

[billy the kidd]

Are you sure you didn't get the air filter wet when washing it?

it maybe got a little wet , but i dried and reoiled it and it still seems to be doing it,,,

[tribalbc]

it maybe got a little wet , but i dried and reoiled it and it still seems to be doing it,,,

It just seems coincidental that this started after you washed it, and water in the carb/intake will give you the same syptoms.

Check the intake boot is dry and remove the drain plug on the carb. Any water that gets in the carb will sit at the bottom and take a while to get rid of.

Otherwise lean jetting would cause these syptoms and colder weather will cause you to be leaner. But you would have been close to running lean before in warmer conditions to have that drastic of change in running.

Does it run better warm than cold = lean

Do a pilot circuit check to start in the jetting stickies.

Wacking open the throttle on the stand will cause almost all 4 strokes to stumble. Does it do it when riding?

[billy the kidd]

to answer the last question ,, it did stumble once or twice while rideing , only if i reallly snapped the throttle open from a low rpm,,, i assumed that it must have been close to lean prior to the cold weather, like i said i think any jetting that may have been done after the mods would have been done for alot warmer climate

[tribalbc]

to answer the last question ,, it did stumble once or twice while rideing , only if i reallly snapped the throttle open from a low rpm,,, i assumed that it must have been close to lean prior to the cold weather, like i said i think any jetting that may have been done after the mods would have been done for alot warmer climate

But when the bike is cold (engine) does it stumble then get better as the engine warms up?

[billy the kidd]

But when the bike is cold (engine) does it stumble then get better as the engine warms up?

a little , but it never goes away,, i didnt notice it when riding on warmer days,,,, i just drained the bowl and found a very small bit of water, through the drain tube, i then opened the large plug , but couldnt catch the fuel so i dont know if there was any there,,, i pulled the plug, and it is mostly black, except the tip of the electrode, witch is white,,,, after putting the bike back together, i took it for a ride after i let it idle for about two minutes or so,, i took it up the hill and rode around for about five minutes and i can still notice a little stumble on a fairly quick snap open,, on the kick stand if i try to quick snap it open it will die,,,,,

[tribalbc]

Try this first

https://www.thumpertalk.com/forum/showthread.php?t=327405

[tech24]

everyone here is probably on the right path but just wanted to mention.......did the spark plug well get water in it? I've done it plenty of times but never on these motors cause the coil seal pretty good...just a thought

[billy the kidd]

tried that a couple of times,,, at a fairly low idle if i turn in the screw it starts to stumble but dosnt die, it sounds like it is going to if you were to leave it be for a second, but i thought it should just die. i then back it out until it smooths out some where 1 1/2 to 2 but it dosnt run seem to be very snappy so if i go out 2 1/2 it seems to be the best,, again if i snap the throttle open fairly fast it will just stumble a little, but if i snap it open as fast and full as i can ,, it just shuts off, dies,,, does it sound like i may be lean,,,, i wish i had some warm weather in the future to test my theroy,, but it looks like it is going to stay in the low 40s to high 30s the next week or so,,,,,any idea what the main jet size should be,,,, maybe ill see if i can pull it and see what it has in it,,, this is really starting to bother me ,,,,, by the way it dosent seem to have had any water around the spark plug,,, the boot seemed to be sealed fairly well,,,

[tribalbc]

,,,,,any idea what the main jet size should be,,,, ,

168 to 170

[billy the kidd]

ok ,,, so i pulled the main and i found a 168 , the cold weather im having is between the 30s and 40s , and according to this chart i should be in the 172 range,,, again im at 800 ft. or so,, on the warm days it was in the high60s to low 70s and again according to this chart i had the correct jet for that ,,, so my question now is should i go up,, or am i just bullshitting my self into believing this is the problem?

so should i go 170 or all the way to 172 ,, the problem is in the summer it easily gets in to the 110s-115s in the spring it is usually 70s-90s so i dont want to go to far and have to change it for the season

before i forget thank you very much for helping me with this ,

Elevation 0 to 4,000. feet

30 to 45 degrees: 172 main, JD Blue #5, 48 Pilot, 2.0 turns, 75 starter jet, #0 leak jet

45 to 60 degrees: 170 main, JD Blue #4, 48 Pilot, 1.75 turns, 72 starter jet, #0 leak jet

60 to 75 degrees: 168 main, JD Blue #3 or JD Red #5, 48 Pilot, 1.5 turns, 70 starter jet, #40 leak jet

75 to 90 degrees: 165 main, JD Red #5, 48 Pilot, 1.25 turns, 68 starter jet, #50 leak jet

90 degrees plus: 160 main, JD Red #4, 45 Pilot, 2.0 turns, 65 starter jet, #60 leak jet

[tribalbc]

If you're in the 30-40 temp range, low elevation a 172 wouldn't hurt. But be prepared to change that when it's hot.

Main is only 3/4 - full throttle range but does effect the needle.

You should see what size your pilot is. A 48 would be right.

Otherwise try raising your needle a clip.

I have YZ exhaust system and extra modded open air box and I run 168 main, 45 pilot 500-4000ft. When it's cool like your temps it's not optimum but still runs decent.

[billy the kidd]

thanks, i just took it for a ride,, and it didnt seem too bad,,go figure,, i cleaned the main while i had it out,, who knows, i was going to take the carb out or spin it, and see what pilot jet is ,, but wow ,, what a nightmare to get to everything, i think that if it gives me any more trouble, this may be one of those things i let someone else deal with,,,lol ill just take it to the shopand have them check the jets while im on the subject,, and have audiance i keep a drum of leaded 110 octane fuel in the garage for my jet boat,, will it hurt to mix a little into each tank of fuel,

[tribalbc]

thanks, i just took it for a ride,, and it didnt seem too bad,,go figure,, i cleaned the main while i had it out,, who knows, i was going to take the carb out or spin it, and see what pilot jet is ,, but wow ,, what a nightmare to get to everything, i think that if it gives me any more trouble, this may be one of those things i let someone else deal with,,,lol ill just take it to the shopand have them check the jets while im on the subject,, and have audiance i keep a drum of leaded 110 octane fuel in the garage for my jet boat,, will it hurt to mix a little into each tank of fuel,

Yeah I still think it could be a water problem and could get better.

No harm or gain done in using the leaded 110