spark plug eater

YamaB · Apr 4, 2004

I just bought a 99 yz250 and it is going through spark plugs like crazy... It seems to run fine, but after about 30 minutes it just up and dies... Inspecting the spark plug, the end is completely black...

The throttle response seems good and power is very snappy... It "seems" to flatten out a bit at the top of the rpm range, but I'm not sure how it is supposed to feel as this was my 1st time on the bike. It does have a pro-circuit pipe and silencer on it... I am a total noob and don't know a thing about tuning carbs... Any suggestions??

thanks,

Brian

biglou · Apr 5, 2004

I suggest bringing her over to Lou's Monster Garage! :) Seriously, if you don't get it sorted before the weekend, I'm sure we can find out what's going on. :thumb:

ben.handasyde · Apr 5, 2004

use a fully synthetic oil and change to a NGK iridium tip plug running 40:1

YamaB · Apr 5, 2004

I bought some iridium plugs so I'll see if they help. As for oil, I'm using Klotz R50 oil.

I'm a bit confused on jetting. Does anyone actually sell a jet kit for a dirt bike?? None of the web sites I've seen offer them. Also, there is a main jet, pilot jet, and needle?? What should I start with??

- BA

gwcrim · Apr 5, 2004

Sounds like you need to lean out the pilot and/or needle. Jet kits & expen$ive spark plugs are usually a waste of money, IMO.

If you want to try something on the cheap, try lowering the clip on the needle. But cheap isn't always effective. I'd wager that your pilot jet is too rich.

Find out what pilot jet you have and go about 2-3 sizes smaller, considering how bad your problem is. Once that is done, readjust your idle mixture screw and the idle speed screw.

I'm not sure about your application, but there are plenty of carb tuning guides to be found online. They'll take you step by step through a proper jetting sequence.

YamaB · Apr 5, 2004

Thanks for the advice... I'll probably try to lower the clip (have to research on how to do this), and if that doesn't help I'll change pilot jets... Any chance it could be the main jet??

I guess 1st things 1st I better yank that bugger out of there and get my hands dirty...

- Brian

souphmars · Apr 5, 2004

if u riding it hard, and then it does it, try lowering the main-i have a 1998 yz250-i have been having plugs fouls like crazy too-i have an fmf fatty and an fmf shorty silencer-i have tried the needle clip, and the pilot-right now i am experimenting with the main jet-i have put new reeds in it and topend, cleaned the carb countless times, and had the float adjusted-i am still experimenting

zoommx · Apr 5, 2004

On my 98 yz, I once had a bad fouling problem a couple years after I had been riding it. Since riding conditions and jetting hadn't changed I didn't know where to start. The top end turned out to be in spec, so I went looking at the ignition. Measuring the coil, I found the resistance was out (of spec). It was supposed to be about 28 ohms or so and it was in the upper 30s range. But measuring to the tab coming out of the coil the thing was o.k. After cleaning up the pathway to ground, I haven't fouled like that since.
:yeehaw:
MahaRog

souphmars · Apr 5, 2004

could u explain that more zoommx??did u have any other porblems???when did it foul the plug??i have been wondering about my ignition-

sunnyboy · Apr 5, 2004

lowering your needle is the place to start,you need to check with your dealer to see what the stock jetting on the bike is supose to be and change to those jets to stock.your dealer can get them for you.while you are thier get a set of manuals for your bike owners and a shop manual will help you with your mantainace and other usful info.once you have the stock jeting in your bike take it out for a short ride and check the plug using a new plug each time if the plug is still black lower the needle one notch and try again,you want the plug to look brown.i dont like the oil you are using i used to be a big klotz fan intell i had a problem years back my tuner told me it did not have the luberisity needed to lube the rings,i disasimbled the top end and found the ring groves in the piston were full of carbon,i replaced the rings and cleaned the piston ,put it back together and changed to golden spectro at 50-1 and never had the problem again-this would be somthing to remember while you are checking out your jetting

zoommx · Apr 5, 2004

Soup,
No other problems at the time. Bike would foul at any time. Hot or cold, mx practice or trail riding. I believe the main source of resistance to the frame ground was where the tab coming out of the coil assy is spot welded to the laminated bars. I put some flux in there and heated a little, then put some oil to prevent further rust, checked resistance (back to normal) and rode. All good now. I imagine that a little corrosion around the mounting screws could have the same result. I don't have my manual with me right now or I would let you know where the resistance is measured and what the spec number is. I think it was from the orange wire to ground, 24-28 ohms, but I'm not sure about that. May have been from the plug wire to ground.
Roger

RAH RAH · Apr 6, 2004

from the description of your problem its seems as though that either the ignition is breaking down or that you have too rich of a main jet if its in the upper rpm range.

Rm250sRalRight · Apr 6, 2004

Zoommx, you could very well be godsent!
I have been scratching my head for a while trying to figure out why the heck my 96 RM250 fouls up plugs about each hour. It used to run fine for about 1.5 years then this.
As I read through this forum (amazing source of knowhow, you guys rule) I learned a few things and am in the process of trying them. Last night I played with the floats in the carb, didn't seem to help much.
Now I come across your msg about the ignition coil. Sounds like a promising lead. However I don't know much on how to test it, to be honest I don't even know where it's located. I have a voltmeter, is this what you use to test for ohm values? If so, how is this done? With the bike running, etc? Please describe the process in detail if you can, I want to take a closer look at this. A friend thinks it could be oil leaking from the crankshaft seal although I'm hoping to try the simpler things before the hassle of replacing that seal.

Please provide as much detail as possible, even links to good sources online, if you wish.
As is, the bike fouls up and I have already changed the jetting, adjusted the floats, changed the mixture (running Yamalube R2 at 40:1). Nothing seems to help. I think you may be up to something here regarding this ignition coil.
Thanks

zoommx · Apr 6, 2004

Your friend could be right about a leaky seal, but testing the ignition is alot easier.
A multimeter can be used to measure. Just set it to the ohm scale, (it may have a symbol like the greek letter omega)
The "ignition coil" is where the spark plug wire goes. Usually the gas tank will need removed. I don't know the values your bike should be, but I'll give you the info about my 98 250, which btw, the numbers for my 100 and 490 are much different. none of the 3 are the same.
Ignition coil inspection: Primary side-test lead + to orange lead, test lead - to black lead, .20-.30 ohms at 68 degrees F. Secondary side: + to spark plug lead, - to orange lead; 9.5k - 14.3k ohms at 68deg. Note, when inspecting the secondary, remove the sparkplug cap.

You can also check the pickup coil and source coils resistances while you're right there at the plug with 6 or so pins. pc: Mine is + to white/red lead, - to white/blue lead 248-372 ohms; sc1 + black/red, - green/white 720-1080 ohms, sc2 + green/blue, - black 44-66 ohms.

souphmars · Apr 6, 2004

sorry zoom but can u give some pics or something-around some of my ignition components i do see some rust and corrosion-this would help me out alot at giving me a better pic of it-do u have an aim, if so email it to me if u can-if the seals were leaking u would see oil coming out of the exhaust or u might be able to see iti n the cylinder or carb-

YamaB · Apr 6, 2004

Does anyone think that running a br7es might serve as a temporary fix... Will I risk tearing up my bike in doing so??

Anyway, I'm a total ignoramous when it comes to carb tuning (learned alot on here and from Lou's emails though), and am worried that if I tear my carb down tonight, that I won't have it back together by the weekend... I REALLY want to do some more riding this weekend...

For now, my bike is getting 100% trail use if that matters...

- BA

YamaB · Apr 6, 2004

In taking apart the carb, it has a 160 main jet and a 38 pilot jet... Lean as heck... Not sure on the needle as I can't figure out how to get it out... I guess I'll take a look at the coil... Any other suggestions... Any other yz250 riders have jetting reccomendations??

thanks,

Brian

YamaB · Apr 6, 2004

Not sure if this is relevant, but one of the outlet tubes from the carb was jammed in the rear shock joint and completely pinched closed...

- BA

zoommx · Apr 6, 2004

souphmars said:
if so email it

I would email stuff if I knew where to send it. you can email me at zumx@aol if you want.

Roger

souphmars · Apr 6, 2004

i am goin to try a new mix called opti2

YamaB · Apr 6, 2004

My coil mounts are quite rusty indeed... I'll have to clean them up and see if it fixes the problem... Think I'm going to wait til I re-jet though (172/42)... If the coil is the problem, I'd hate to fix it and end up with a fried piston because the bike is currently set waaaay to lean (at least based on the scale in my manual -> 160/38)...

- BA

Rm250sRalRight · Apr 6, 2004

zoommx, I'm working on my bike as I write this and I hope to catch you still online.
Please clarify this to me: you mean that I connect the +(plus) lead - or the red lead from the multimeter onto the orange wire - and connect the -(negative) lead - or the black lead from the multimeter onto the black wire coming from the coil. I suppose you are referring to the 2 wires that connect to the coil and is sitting inside a white plastic case (mine are actually black and white, guess I'll just assume that yours is orange instead of my white). If this is correct, please acknowledge.

As for the secondary test, I'm a bit confused. Do you place the + lead from the multimeter right onto the metal piece that connects to the spark plug? Obviously I have it off the plug - but must I remove the other end of the coil or can I leave the coil where it is for the sake of testing it? Sorry if this sounds redundant, it's my first time doing this and I want to be sure I have this right. Thanks again for the help.

dirtRiceburner · Apr 6, 2004

I didn't read all the advices but most of them. I noticed on a couple of them it said to lower the clip on the jet needle. Don't. You need to go up! This will lean it out. And if you can't raise it anymore, you may have to get a thicker needle. It is also adviseable to do any jetting after the bike is warmed up otherwise the bike will have tendency to run too lean and that could damage your engine real fast. In fact, if you drop down on the main jet and the pilot (slow jet) too many, too fast, it will run too lean and damage the engine.
A simple test is to adjust the air mix screw while the bike is running. If there isn't any noticeable changes as you either open or close, the pilot is too big. If it's too small, you will see instant changes.
Another thing you may want to check other than the carb is to make sure the coil has a good ground. Sometimes the screw that holds the coil on to the the body, aka ground screw, gets some rust and may not have a good contact.
Don't buy anymore expensive plugs. Get the B8es for 2$. They work fine. Lastly, rev the bike more as you ride. This is a good habit to have. It will burn off the excess oil on the plug. Rots of rock!

souphmars · Apr 9, 2004

i think my problem is my crank seals-that won't be easy

Rm250sRalRight · Apr 10, 2004

Souphmars: I suspect I may have the same problem and a friend who is great working with bikes has a test in mind that he says would give us a definite answer, as to whether the problem is with the crankshaft seal.

Here's what he said the test involves: remove the carb, remove the pipe, seal off the exaulst port and something else (sorry, can't remember all the details) and then you force air into the engine and listen for any air leaving through the seal. He says it's a simple procedure and I fear I may have to have that done in a few days, should my bike not run well tomorrow.

I'll keep you posted. I sure hope it isn't the seal, as the time required to replace it is ridiculous.

spark plug eater

biglou

Similar Topics

Privacy & Transparency

Privacy & Transparency