86 ATC250R fouls plugs - bigtime

[NewfieBish]

Hey all! Been a while, but I've been having the same old plug fouling issues since rebuilding the 250R as before the rebuild. I've been using NGK plugs, both BR9ES and BR9EG with no real success. I get maybe an hour runtime outta a plug, it fouls, I pull it out and it usually looks wet and black.

If I use a wire wheel on the plug it may work for maybe another 5 minutes but it'll be very misfire-ey, so I usually toss the plug, get another in it and it'll fire right up and run smoothly. I have been thinking its got something to do with jetting, since that's about the only thing I havent replaced on the bike with the rebuild that could likely cause fouling. Its got new piston rings, head gasket, new K&N air filter. So what do you guys think? And how would I order new jets, Honda has them but they have a wide range. This bike's cylinder bore is stock and so is the exhaust.

Thanks again to you roosters who surely know this off the top of your heads

[j4duncanr]

im going to guess center case gasket or right crank seal.mine was center gasket after my rebuild but you didnt specify you had split the cases.

[bkm]

What ratio are you mixing your oil and since you say its stock I am assuming your jetting is stock also?

[jmax857]

do a leakdown. save yourself some headache.

[TtownJoeShow]

you need to re-jet it since you put the k&n on. do a search for "jetting" or "jetting for performance" it will state that you need leaner main jets fersure... and it could be a leaking tranny case gasket..that is if you split the cases, cant see them just leaking... you might just be putting too much oil in your gas too.

[NewfieBish]

Well to answer you guys, I never split cases during rebuild, I redone topend. Jets are stock. Also gas is mixed 40:1, and it smokes alot during warmup, and maybe sometimes during riding. I noticed that it wouldnt idle when I first bought it. Now that Ive been mixing its gas, its began idling with the screw screwed in alot but it still fouls plugs and smokes alot.

[AtcFactoryRacer]

If your plug is black it is obviously too rich, your need lean it out some but not too lean, the plug should look cinnamon brown at proper jetting, if it looks white it is too lean. When i do my jetting i start the bike and let it warm up to normal operating temperature, then i go ride it and open the throttle up, when i pull back in my garage i do i high rpm shut off to make sure that the plug is burning hot before the engine is shut off, then i immediatly pull the plug out to look at it. After you examine the plug you will be able to tell how it is burning and which direction you need to go with your jetting. Make your adjustments and do the same process again to see how you effected your jetting, you may have to repeat the process many times until you get your plug burning brown

[bkm]

Well to answer you guys, I never split cases during rebuild, I redone topend. Jets are stock. Also gas is mixed 40:1, and it smokes alot during warmup, and maybe sometimes during riding. I noticed that it wouldnt idle when I first bought it. Now that Ive been mixing its gas, its began idling with the screw screwed in alot but it still fouls plugs and smokes alot.

Have you checked your transmission fluid lately? It may have a bad crank seal and its pulling trans fluid into the crankcase.

[pablo]

I had the same problem a few years ago with my 85R.

I recommend getting a carb rebuild kit first. Approx. $18 for a Moose kit. Read the service manual for carb settings for your area (altitude and temp).

Then beg borrow or steal a vacuum tester. It will tell you if your case gaskets are sealing good or leaking in air.

[RubberSalt]

When turning the air screw in, your riching up the pilot jet. You man have your needle clip off a notch or 2. Heres a simple tuning guide.

Put a new plug in, give it 1/4 thottle while riding it for a minute or so, kill it at 1/4 throttle and then pull the plug. Like stated, it needs to be cinnamon brown on the porcelin around the elctrode. Once it's brown, either clean the plug, or get a new 1. Do the same procedure at wide open throttle. Kill it after riding WOT for a minute or so, check the plug. If it's black - you need a smaller main jet, if it's white, you need a richer main jet. Once you have the main jet figured out, it's time for the needle. Start with the needle at the middle clip position. Ride around for a minute, new plug, at 1/2 throttle. Check plug, if black, lower the needle(move the clip up 1), if white, raise the needle(move clip down 1).

[jmax857]

you need to re-jet it since you put the k&n on. do a search for "jetting" or "jetting for performance" it will state that you need leaner main jets fersure... and it could be a leaking tranny case gasket..that is if you split the cases, cant see them just leaking... you might just be putting too much oil in your gas too.

you couldnt be more wrong. first of all if anything he would want to richen the main jets when installing a higher flow filter. and secondly you shouldnt even need to re-jet when installing a higher flow filter.

i stand my my first statement. you can fiddle with the carb for a month and get it to run good for 5 mins here, 5 mins there, to eventually find out at a later date your crank seal is toast, or your centre case gasket. Do a plug check and look at a symptoms chart, if you have any signs of coolant burning, or oil burning. do a leakdown. it will save you a tonnnnee of headache, i've seen it a million times.

[TtownJoeShow]

you couldnt be more wrong. first of all if anything he would want to richen the main jets when installing a higher flow filter. and secondly you shouldnt even need to re-jet when installing a higher flow filter.

i stand my my first statement. you can fiddle with the carb for a month and get it to run good for 5 mins here, 5 mins there, to eventually find out at a later date your crank seal is toast, or your centre case gasket. Do a plug check and look at a symptoms chart, if you have any signs of coolant burning, or oil burning. do a leakdown. it will save you a tonnnnee of headache, i've seen it a million times.

hmm well when i built my2 trikes, rad valves, bigger carbs, k&n and piped, it all depends what you put on. some upgrades require leaner and some require richer jets... my plugs would last 2 or 3 months, riding every weekend.... when you buy a brand new PWK, they give you a booklet on how to jet for performance.

[jmax857]

i've told a few people that you dont need to re-jet after a filter change, no one understands me. i used to think the same thing. i read a very very good article online that explained why you shouldnt have to re-jet. ill try and find it. basically the way a carburetor works is the air flowing through the carb atomizes the fuel right? when you install a higher flow filter, it gets a higher flow of air through the carb. the more air that flows through the more fuel it atomizes. so in theory the more air that flows through the carb, the equal amount of fuel to air is still pulled into the engine.

[RubberSalt]

I have to agree with jmax. Th eonly true way to know if you have a leak is a leak down, cap the exhaust, make another crap with shradder valve that you stick in the carb boot, fill till about 7 psi. Wait an hour, if you lose no pressure, your good. If it drops any, get soap water and spray all over the engine, case valves, cylinder ->case, head, spark plug, intake, around the leak down(make sure it doesn't leak). If it leaks and you check everything, check the crank seal on the flywheel side, if it leaks then.. take the clutch cover off. If it leaks then, you missed something.

Usualy an air leak means your lean though.

[NewfieBish]

Drained the oil off today, it was black as oil gets with us of course, but before I say anything else: what does bad transmission oil look like? And thank you for your responses, I'm going to try to mix the next tank of fuel a little lighter, since I mixed this one a bit heavy where it was its first tank since rebuilding the topend with new rings.