why is my bike doing this

[ftw666]

99 yz 250

on a cold start up my bike fouls a plug (black and wet) but as soon as i put a new plug in the bike it runs great. when im done riding i take that plug out and check it and its tan and looks perfect .
then the next day i ride on the plug that i used the day before that i checked, it fouls that plug on start up.
i have done spankys rejeting tips and i dont know what the hell the problem is.
40:1 mix
clean air filter
bikes not using any tranny oil
anyone know whats going on?

 

[kshackleton]

Perhaps your pilot circuit is too rich? Have you tried starting it cold with no choke?

 

[ftw666]

i have done it both ways but when i use the choke i only use it to start the bike i turn it off as soon as the bike starts

 

[kshackleton]

i have done it both ways but when i use the choke i only use it to start the bike i turn it off as soon as the bike starts

So even starting the bike cold with no choke it fouls the plug. Does the bike idle reliably when warm or does it eventually load up and die?

If I was in your shoes, I'd be thinking that the pilot circuit is too rich.

Maybe the float level is too high?

 

[ftw666]

the bike idles fine and with a new plug it dosent load up. its only on cold starts that if fouls plugs. i have a 162 main jet with a 48 pilot jet, needle at the second clip from full lean and just had a shop look at my carb and they said everything was in perfect order (float level, no dirt,etc) its has been baffeling me for 3 weeks. if i were to change the pilot jet what should size should i go to?

 

[kshackleton]

the bike idles fine and with a new plug it dosent load up. its only on cold starts that if fouls plugs. i have a 162 main jet with a 48 pilot jet, needle at the second clip from full lean and just had a shop look at my carb and they said everything was in perfect order (float level, no dirt,etc) its has been baffeling me for 3 weeks. if i were to change the pilot jet what should size should i go to?

So...prior to 3 weeks ago...all was fine? Did anything change? It seems odd that the existing jetting would have been fine before and now there's a problem.

if you do change the pilot....don't reduce it by much and see if that makes a difference.....but if this is a new issue, perhaps something else is going on.

 

[darringer]

Sound like th pilot. Try changing to a 45 or even a 42 and see if the problem goes away. If you end up running too lean of a pilot during testing , it's no big deal. The bike won't seize because of it.

 

[ellandoh]

let it idle with the choke on for longer, without ever touching the throttle, after 45 seconds then shut the choke and continue to let it idle til you can give it gas without killing it

 

[ftw666]

heres the scoop on this bike
i bought it off a friend of mine for dirt cheap last year and it ran awesome.
then this year it ran great early in the season (colder weather)
then all of a sudden it started fouling plugs so i took it over to a friend of mines house who races and he thought that the bike was over jetted for the type of riding i do( woods riding the kid i bought it off of ran mostly tracks)
so we decided to change the main from a 172 to a 165 and the pilot jet from a 50 to a 48. the needle is at the second clip from full lean( moved the needle to the top clip and it didnt help) and the floats look fine, and the air screw is 2.5 turns out.
and it still did it. so then i decided to do a top end rebuild and i also bought a pipe and v-force reeds. after the rebuild it still did it. i ran it for a while and i always fouled a plug on a cold start. so yesterday i put a 162 main jet in it becaues it still is running rich and the bike runs better then ever but it still fouls on cold start. so today i put a 45 pilot in and the bike ran like crap(wouldnt idle and it would bog every time i gave it gas so i put the 48 back in and it ran awesome again but it still fouled on a cold start. i noticed today the when i started the bike that some gas was comming out one of the overflow tubes from the carb which tells me that its getting to much gas or not enough spark on startup none of the shops around my area know what to do. ive been through about 15 plugs in 2 weeks and im running br8es/br8eg also tried a 7 but it didnt help

 

[ellandoh]

when you changed the pilot did you then adjust the air screw?? for better idle

 

[ftw666]

yea but the bike didnt feel right no power on the bottom end and also i put that pilot in before i started the bike today and it still fouled the plug on startup

 

[steve.emma]

just my 2 cents worth here but maybe the float needle valve is a bit worn and/or the fuel petcock dribbles fuel even when turned off? i have had this on older model yz's and it causes fuel to leak into the crankcase or air boot area. when you start for first time the extra fuel plus the choke being on causes a over rich condition that makes the plug foul. you could try disconecting fuel line and draining carb after use.
good luck!

 

[2-strokes-4-life]

if you have gas pouring out the overflow you may have a float issue.was the bike sitting upright when it dumped the fuel?if the float is sticking open it could be flooding the motor and causing you to foul plugs

 

[DLHamblin]

99 yz 250

on a cold start up my bike fouls a plug (black and wet) but as soon as i put a new plug in the bike it runs great. when im done riding i take that plug out and check it and its tan and looks perfect .
then the next day i ride on the plug that i used the day before that i checked, it fouls that plug on start up.
i have done spankys rejeting tips and i dont know what the hell the problem is.
40:1 mix
clean air filter
bikes not using any tranny oil
anyone know whats going on?

What plug are you using?

 

[SQUIRLEYMOFO]

In my experience the V-force reeds make them harder to jet. In fact if the Kehien carb doesn't help clear my CR up I may put the stock reeds back in it. With the stock TMX carb it was either to rich, or down on power.........

 

[Micahdawg]

Plug type and gap is something to consider.

Micah

 

[ftw666]

my local shop said my floats are fine and everything in my carb is in workin order. using a br8es plug. and i just cleaned out my fuel tank and petcock and the petcock is working fine. i can start the bike with the petcock in the off position and it still fouls plugs. even with the tank disconected using just the fuel in the carb and still fouls. using the gap setting in my book

 

[kshackleton]

my local shop said my floats are fine and everything in my carb is in workin order. using a br8es plug. and i just cleaned out my fuel tank and petcock and the petcock is working fine. i can start the bike with the petcock in the off position and it still fouls plugs. even with the tank disconected using just the fuel in the carb and still fouls. using the gap setting in my book

Could this be an ignition problem? I am thinking that the spark while kicking the bike over might be weaker than when it's running due to a slower rotational speed. It doesn't light the fuel right away and the plug fouls.

As far as starting goes....on my KX250....I have to keep the throttle closed while starting.....hot or cold....I use choke while cold....kick it with no throttle....it usually starts on second kick....then I let it idle with choke on for 30 seconds.....then choke off and let it idle for another minute before riding. If I open the throttle while starting....it's usually not a good thing.

 

[ftw666]

i also thought it might be and ignition problem a mechanic told me that my coil might be bad but he wasent sure he said mess with the jetting before you start with ignition

 

[trev]

hey if you find out what's wrong let me know cuz my bike is an 01 yz 250 and it does the exact same thing my e mail is [email protected]

 

[E-man811]

my local shop said my floats are fine and everything in my carb is in workin order.

Take this with a grain of salt.

You have one of a few issues, I doubt any of which is a jetting problem. Not to say that your jetting couldn't be improved, but I don't think it is causing your cold start problems.

Could be.....

1 Fuel leaking into the crankcase through the float. Either mal-adjusted or the seat is in poor condition and is leaking. Take the bowl off and inspect this with your own eyes before you do anything else. Based on your info and your comment about fuel from the overflow lines, this seems the most likely.

2 Transmission oil seeping into the crank case through a worn drive side seal. Could be bad enough that it's happening when sitting or just bad enough that it sucks a bit when cold.

3 Air filter that is over oiled or motor oil is being used on it. Have seem both of these plenty

4 Ignition problems. However, they will usually work or not work, or exhibit problems while the bike is running.

BTW, does your bike ride home in a trailer or in the back on a pickup, if so, make sure that the fuel is turned off.

Open you carb, inspect the float level and the float needle and seat, then report back.

 

[DLHamblin]

my local shop said my floats are fine and everything in my carb is in workin order. using a br8es plug. and i just cleaned out my fuel tank and petcock and the petcock is working fine. i can start the bike with the petcock in the off position and it still fouls plugs. even with the tank disconected using just the fuel in the carb and still fouls. using the gap setting in my book

A BR8EG is standard (at least on newer model YZ's), a BR8ES will work (and is cheaper) but will be more likely to foul than the EG version.

 

[ftw666]

well the other day i started my bike differently and it didnt foul a plug on warm up. i dont know if i just got lucky or if my bike is just being difficult. but tomarrow im going to start it the same way i did it the other day. well see what happens. thanks alot for the info.

 

[kshackleton]

well the other day i started my bike differently and it didnt foul a plug on warm up. i dont know if i just got lucky or if my bike is just being difficult. but tomarrow im going to start it the same way i did it the other day. well see what happens. thanks alot for the info.

What did you do differently?

 

[teknition]

heres the scoop on this bike
i bought it off a friend of mine for dirt cheap last year and it ran awesome.
then this year it ran great early in the season (colder weather)
then all of a sudden it started fouling plugs so i took it over to a friend of mines house who races and he thought that the bike was over jetted for the type of riding i do( woods riding the kid i bought it off of ran mostly tracks)
so we decided to change the main from a 172 to a 165 and the pilot jet from a 50 to a 48. the needle is at the second clip from full lean( moved the needle to the top clip and it didnt help) and the floats look fine, and the air screw is 2.5 turns out.
and it still did it. so then i decided to do a top end rebuild and i also bought a pipe and v-force reeds. after the rebuild it still did it. i ran it for a while and i always fouled a plug on a cold start. so yesterday i put a 162 main jet in it becaues it still is running rich and the bike runs better then ever but it still fouls on cold start. so today i put a 45 pilot in and the bike ran like crap(wouldnt idle and it would bog every time i gave it gas so i put the 48 back in and it ran awesome again but it still fouled on a cold start. i noticed today the when i started the bike that some gas was comming out one of the overflow tubes from the carb which tells me that its getting to much gas or not enough spark on startup none of the shops around my area know what to do. ive been through about 15 plugs in 2 weeks and im running br8es/br8eg also tried a 7 but it didnt help

If you have fuel coming out of the over flow tube when the bike is standing up straight you have one of 2 problems.
1) your float level is too high.
or
2) your float needle and seat are not seating properly.

Throw a needle and seat in it and adjust the float level to the spec in your service manual before continuing on with anything else as all carb circuits will be affected by improper float operation.

Tek