2002 Cr125 fouling out on start-up *EDIT* Running REGULAR 87 Octane GAS

[charlevoixboy]

I've got a nice 2002 Cr 125 that will foul its spark plug while starting it. The bike is completely stock, pipe, reeds, air filter- all stock. Runs great and starts 2nd kick every time. Upon starting it up you have to rev the heck out of it (12,000+ RPM) to let the fuel that accumulated upon shutting down, clean out of the engine. It smokes vigorously for 10 seconds then will clear up. I always shut the petcock to "off" ,duh, after shutting down. Once it's warmed up, it'll start 2nd kick, with no fouling issues. Just if you don't rev it- it'll surely foul the plug. Sometimes it will foul even if you rev it. I've gone through like 8 $6.50 plugs and don't want to start changing for a hotter plug because I ride it in fields and it's not an issue when it's warm. The carb has had its air screw set to 2 1/8 turns out just as the manual says. I'm running Klots oil in it, top-of-the-line. 32:1

I'm just tired of fouling plugs and having my cousin laugh at me with his CRF150F saying: "yep it's a 2-smoke!" because I foul a plug. I'm running regular gas. Plug is golden brown and looks great once warm. Currently the bike fouled a plug and now wont start because it in a "hole" since a new plug will almost clear all the old fuel out- then also foul. The process is then repeated. ? So it's sitting with no plug in it right now and airing out. The bike gets good spark (blue).

From one bike owner to another: Everything on the bike is in GREAT CONDITION! I'm mechanic-ly inclined if that helps! Spark, fuel, air screw, filter, oil, plug EVERYTHING. I've yet to crack the carb because it runs great save for this issue, and the fact that I don't know what jet sizes to change out. ?

Please post with any info you have! It'll help another dirt-biker (2-stroker) out

[charlevoixboy]

Bump......

[Videon07]

That's really odd. I know stock bikes tend to be jetted a bit rich. Try leaning it out a bit. You said you already messed with the air screw but try messing with the jets. I don't know a damn thing about jetting a bike though so someone else will have to help you with that.

[charlevoixboy]

I found this article: http://www.motocrossactionmag.com/me2/dirmod.asp?sid=&nm=&type=news&mod=News&mid=9A02E3B96F2A415ABC72CB5F516B4C10&tier=3&nid=250DEDD54E4C4FFE84F8E5298E89749D

I'm going to try some of those jets in my bike, any help is appreciated!

[charlevoixboy]

Anyone else?

[anthony250]

well if your out that far out on the airscrew then you need a smaller , leaner slow jet "pilot jet" / everything else is good 32:1 Good/ just smaller slow jet you can get online or at you local mx dealer buy one or two steps smaller "number on the jets" if it gets better keep going smaller till its good and read the other link!, and look at the chart it really helps and read this !!

https://www.thumpertalk.com/forum/showthread.php?t=412662

heres what the effects do

[charlevoixboy]

Would running Regular (87 Octane) gas make the bike foul on start-up???

[anthony250]

maybe ? try running something around 91 , give that a try

[dmcca]

Would running Regular (87 Octane) gas make the bike foul on start-up???

No, that alone wont make it foul. Sounds like your pilot jet and possibly your needle clip position are too rich.

What elevation and temp are you riding at? What are the current jetting specs? Start with this data then you can work out where to go from there.

You also need to make sure that the engine is in good condition, do a compression test and make sure that the top end is in good condition. Does it use trans oil?

[charlevoixboy]

I'm at 664' above sea level at 60-85 degrees F. I've never cracked the carb, and I'm the second owner. Previous owner said they had only done one top-end once, a few months before I bought it (before the winter, fall maintenance for next season) Previous owner seemed very honest. If it was using tranny oil wouldn't it smoke all the time? I know the smoke it puts out on start-up is the premix because I can smell the klots.

[charlevoixboy]

Well, turned the air-screw out a little bit (so its around 2 1/2 turns out) and got it running, rode it around and it ran great! Parked it and went to start it about 10mins ago and fouled the plug again! So now I'll rejet. The problem I think it has is that it will run fine and everything, but when you shut it off there is remnants of unburned premix- as the bike sits (24hrs) all the gas evaporates and what you have left is all the oil. You start the bike and all that oil is instantly on the spark plug and not diluted with any gasoline- so it instantly fouls. Would jetting the pilot jet help this? The bike ran fine (golden colored plug) when shut off and in less than 5 secs after starting and the fouling, it looks like this- all the black is wet oil only-no gas. I really can't imagine that jetting would cure that unburned oil?

[Keith72]

did you check your float and float needle?

if its leaking it will make it run rich no matter what your jetting is

[68b_body]

sometimes id have a similar problem as yours. if i don't let it warm up before i ride it and it dies. it would foul the plug and be a pain to start. i would have to let it sit for quite a while before it would start again. long as i let it warm up i have no problems. i also run 87 octane.

[charlevoixboy]

That's a good point. I'll crack the carb and clean/inspect everything especially the float height. The previous owner said "if you don't shut the petcock after you shut the bike off, upon the next start-up it'll surely foul the plug." That leads me to believe in the float height. We'll see when I take it apart.

[charlevoixboy]

Fixed the bike. IT WAS THE FLOAT HEIGHT! I should have taken a pic of it because the float was 3/8 of an inch off! Amazing it was running like that. Starts great now, since it doesn't leak all of the carb and fuel hose's gas into the engine now. Thank you so much for the help everyone!

[mjprice]

I have the same bike get belray h1r oil and mix it to 38:1 if it's still rich try playing with the air fuel screw and drive the bike if it bogs when warm keep adjusting. if that doesn't work get the carb float adjusted i think it should be set at 12mm double check to book the last time i did it was 1 year ago(bad memory) or get a br8es spark plug to bump up the heat range. good luck

[mjprice]

just looking at the puics you posted maybe a crank seal is leaking causing the rich condition.

[fxrs]

sounds like your float is sticking

[phatcat]

Fixed the bike. IT WAS THE FLOAT HEIGHT! I should have taken a pic of it because the float was 3/8 of an inch off! Amazing it was running like that. Starts great now, since it doesn't leak all of the carb and fuel hose's gas into the engine now. Thank you so much for the help everyone!

he fixed it

[Keith72]

just looking at the puics you posted maybe a crank seal is leaking causing the rich condition.

wouldnt a leaky crankseal make it run lean?????