fuel delivery problem

[Cwad_BoyEX]

ok i went to rejet my carb and i did and no matter what jet i put in the carb the spark plug always comes out black so i dont know what the right jet to use, i have my fuel mixture screw is turned out 3 1/2 turns what should i do?

[stupid driver]

get yourself a new plug first, then do some full throttle runs and chop the plug. This will give you a main jet reading. paper bag tan is the color you want. I would also turn your screw in to maybe 1 to 1.5 turns out.

[Cwad_BoyEX]

What do you mean chop the plug?

[JOEX]

Here are a couple of methods that were posted here awhile back......

With all the different kinds of fuel we see (including unleaded) there is no way to get the right color.The way I read a plug is to ride for 10-15 min. to get it up to temp.Run down the road wide open in the top gear and hold it there for 5-10 sec. then kill the motor, pulling in the clucth and come to a stop. Pull the plug and look at the ground strap,you want to see a carbon line in the middle of the 90*bend. If the line is closer to the tip of the strap its to rich. If it is down around the 90* bend towards the plug threads its to lean.This works on 2 and 4 strokes.It does not matter what color the plug is just make sure you use a used plug that has carbon on it.

Mickey Dunlap



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Reading Mr. plug can be Voodoo at best with today's lean fuel. Try this test, I have used it when reading plugs made me crazy.


The Roll-Off technique is the quickest and is almost as accurate as the Roll-On method. First, one gets the engine warm on the way to a safe roadway. If there is room, use fourth gear as this allows more time to assess the result.

Now, get the engine rpm high enough that it is on the cam and in its power band. This may need to be as high as 4000 rpm with some cam choices. Apply full throttle. Let the engine accelerate for a couple of seconds until it has settled in and is pulling hard. Quickly roll the throttle off to about the 7/8ths position. When you do this, the mixture richens slightly for a second or so.
If the engine gains power as you roll the throttle off, then the main jet is too small and you need to fit a larger one.
If the engine staggers slightly or has a hard hesitation, then the main jet is too large and you need to fit a smaller one.


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White_Knuckles

[cals400ex]

first get a new plug. 2nd, tell us what mods you have done to your bike. i will try and help you with what jets to use when you tell us your mods. are you trying to change the pilot, main, and needle or just one or two of them??? i need more info. if you are using the stock pilot right now, i would not turn the fuel skrew out only a turn or two. the stock position is 2.25 turns out and it is lean from factory. so you probally need to be out a little farther than that.