JOHNDOE83
06-30-2010, 12:45 PM
This is based on a 400ex, it will also help anyone running a non EFI atv.
The most controversial subject on here is how to properly read a plug, I have some advice and some facts to clear up and help everyone having jett issues and plug reading problems. I donot plug chop, will explain at the end...
The pocelain "IS NOT" the proper way to read a plug....in fact the porcelain is how you determine timing, detonation....AND partly needle position....even Trinity will tell you the porcelain is not the way to tell proper jetting.
The ground strap "Where your plug sparks to" and "is the base of the threads" determines heat range....and "part" of pilot jet.
The carbon ring, "inside the plugs threaded section" determines your actual jetting...
Determining heat range: Our ATVs dont really apply here being that they are setup for the right plug from the start...but here you go. "The ground strap" this is the piece attatched to the plug threads where the spark hits. If the color on the strap is closer to the end...its to cold...if the color goes almost to the threads on the plug its to hot...you want it in the middle of the strap.
This is only important if you have a crazy built "Highly Modded Motor" NOS...High compression 13:1 or more....custom timing, not 3 or 4 degrees...Alcohol....not even a motor like mine.
The pilot jet slightly affects the gound strap area and the ring around the base of the plug...not really nessesary to check being that you want it a tad rich...like a 42 pilot on a stock carb and a 50 in a 450r carb. If its a nice dark even color and your not poping on decel...your pilot and air fuel screw is fine.
The porcelain: The porcelain shows detonation and timing, also needle position. The "tan color" everyone sees on the porcelain after riding a few hours comes from a proper needle setting only.
If there is deposits on the porcelain "Black or shiny" you have detonation, timing really isnt an issue unless you have that "highly modded motor" stated above...ex's are fine with 3, 4, or 6 degree timing depending on mods.
ACTUALLY DETERMING JETTING: OK, if all the above is ok after riding for a few hours, then you need to do a plug run!
Ride at wide open throttle till fourth or fifth gear, squeeze the clutch and kill the motor, coast to a stop, pull the plug, replace with another, ride back home.
Once back at home, take the removed plug, use a grinder with a metal cut off wheel, hold the plug by the porcelain with your hand or vice grips, cut the base of the threads with the wheel all the way around, THE PORCELAIN WILL NOT GET CUT BY THE WHEEL, becareful anyway to not cut into it....this is why its called a "PLUG CHOP"...lol.
Remove the threaded part and look at the plug, your looking for whats called the base ring. This will be a tiny blackish, tanish ring at the base of the porcelain.
You want this ring to be about 1/8th inch thick, making a complete circle around the plug, and evenly distributed, a lil off is fine.
The thickness also determines needle position, the full and even distribution by the main jet, if your not popping on decel, your pilot/ air fuel screw are fine.
If its slightly black or tanish, your in a good spot.
This stuff is on sites all over the internet, YOU CANNOT go based on pulling the plug and seeing tan.
I donot plug chop, because after extensive plug chops and tunning, what works for me as some of you know, is the "GO BIG OR GO HOME" method.
How its done: I make sure my pilots big enough to start without the choke, I leave the needle in the middle position, and get large size main jets in incriments of 5 from stock size 148 to almost 240..."I have a big bore".
I start with a large size main jet like a 190, then go for a ride, if it doesnt sputter on the topend, I go up 10 sizes, I do this till it sputters at wide open throttle from being rich, then go down to the smaller incriment of 5 till it stops. Your main is now "almost perfect" as close as youll ever get it.
I only adjust the needle if theres hesitation or a slight sputter on acceleration, if theres hesitation, its to lean, if it sputters, its to rich. If your not sure its hesitating, go rich till it sputters on accel and back it off a lil bit till it stops.
This method "WORKS" and is nearly perfect without plug chops.
It will leave you a touch rich, not by much, but BELIEVE ME THATS WHAT YOU WANT....
When you need to rejet: new pipe, new carb, big bore, filter, cams?, popping, backfiring, hesitation, elevation changes, temp changes...etc.
if I left something out, let me know, if Im wrong we can look it up and make proper corrections.
Long but informative...look it up if you have any issues...ask a question if you need to...good luck and ride hard.
The most controversial subject on here is how to properly read a plug, I have some advice and some facts to clear up and help everyone having jett issues and plug reading problems. I donot plug chop, will explain at the end...
The pocelain "IS NOT" the proper way to read a plug....in fact the porcelain is how you determine timing, detonation....AND partly needle position....even Trinity will tell you the porcelain is not the way to tell proper jetting.
The ground strap "Where your plug sparks to" and "is the base of the threads" determines heat range....and "part" of pilot jet.
The carbon ring, "inside the plugs threaded section" determines your actual jetting...
Determining heat range: Our ATVs dont really apply here being that they are setup for the right plug from the start...but here you go. "The ground strap" this is the piece attatched to the plug threads where the spark hits. If the color on the strap is closer to the end...its to cold...if the color goes almost to the threads on the plug its to hot...you want it in the middle of the strap.
This is only important if you have a crazy built "Highly Modded Motor" NOS...High compression 13:1 or more....custom timing, not 3 or 4 degrees...Alcohol....not even a motor like mine.
The pilot jet slightly affects the gound strap area and the ring around the base of the plug...not really nessesary to check being that you want it a tad rich...like a 42 pilot on a stock carb and a 50 in a 450r carb. If its a nice dark even color and your not poping on decel...your pilot and air fuel screw is fine.
The porcelain: The porcelain shows detonation and timing, also needle position. The "tan color" everyone sees on the porcelain after riding a few hours comes from a proper needle setting only.
If there is deposits on the porcelain "Black or shiny" you have detonation, timing really isnt an issue unless you have that "highly modded motor" stated above...ex's are fine with 3, 4, or 6 degree timing depending on mods.
ACTUALLY DETERMING JETTING: OK, if all the above is ok after riding for a few hours, then you need to do a plug run!
Ride at wide open throttle till fourth or fifth gear, squeeze the clutch and kill the motor, coast to a stop, pull the plug, replace with another, ride back home.
Once back at home, take the removed plug, use a grinder with a metal cut off wheel, hold the plug by the porcelain with your hand or vice grips, cut the base of the threads with the wheel all the way around, THE PORCELAIN WILL NOT GET CUT BY THE WHEEL, becareful anyway to not cut into it....this is why its called a "PLUG CHOP"...lol.
Remove the threaded part and look at the plug, your looking for whats called the base ring. This will be a tiny blackish, tanish ring at the base of the porcelain.
You want this ring to be about 1/8th inch thick, making a complete circle around the plug, and evenly distributed, a lil off is fine.
The thickness also determines needle position, the full and even distribution by the main jet, if your not popping on decel, your pilot/ air fuel screw are fine.
If its slightly black or tanish, your in a good spot.
This stuff is on sites all over the internet, YOU CANNOT go based on pulling the plug and seeing tan.
I donot plug chop, because after extensive plug chops and tunning, what works for me as some of you know, is the "GO BIG OR GO HOME" method.
How its done: I make sure my pilots big enough to start without the choke, I leave the needle in the middle position, and get large size main jets in incriments of 5 from stock size 148 to almost 240..."I have a big bore".
I start with a large size main jet like a 190, then go for a ride, if it doesnt sputter on the topend, I go up 10 sizes, I do this till it sputters at wide open throttle from being rich, then go down to the smaller incriment of 5 till it stops. Your main is now "almost perfect" as close as youll ever get it.
I only adjust the needle if theres hesitation or a slight sputter on acceleration, if theres hesitation, its to lean, if it sputters, its to rich. If your not sure its hesitating, go rich till it sputters on accel and back it off a lil bit till it stops.
This method "WORKS" and is nearly perfect without plug chops.
It will leave you a touch rich, not by much, but BELIEVE ME THATS WHAT YOU WANT....
When you need to rejet: new pipe, new carb, big bore, filter, cams?, popping, backfiring, hesitation, elevation changes, temp changes...etc.
if I left something out, let me know, if Im wrong we can look it up and make proper corrections.
Long but informative...look it up if you have any issues...ask a question if you need to...good luck and ride hard.