Pilot Jet Help!

2StrokeBlaster

New Member
Jan 9, 2009
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im not sure wat it is but wen i hold the throttle like 1/4th the way it starts to sputter. i tried messing with the air/fuel screw turning it 1 1/2 ways out and moving it to the right and left. it still didnt seem to fix the problem
does this mean i have to get a bigger pilot jet? if so what size do you recommend?
 
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im not sure wat it is but wen i hold the throttle like 1/4th the way it starts to sputter. i tried messing with the air/fuel screw turning it 1 1/2 ways out and moving it to the right and left. it still didnt seem to fix the problem
does this mean i have to get a bigger pilot jet? if so what size do you recommend?

What is your current jet setup? This seems to be coming more from the main jet, not pilot, is your jetting stock right now? (definitely will conflict with your mods)

Did you just install the mods in your sig? Give us more info, details, etc.
 
I don't know your altitude etc, but with your mild mods, 310 sounds very big. If it runs good everywhere else except 1/4 throttle, try dropping your needle 1 notch. But yeah, I'd say 310 is pretty big. Try a 290 or even 270. I was running 260 with my stock carb with DMC pipe and VF3 reeds.
 
Depending on where you live (temp/elevation) that definitely could be big for just a pipe and a high flow airbox.....but maybe if you're in a different climate from me that could be normal?? If it runs well except there, try the needle clip. I'm no expert but sometimes when you have the jet about right, it just takes a change in the needle to fine tune it.

It could also be rich though....
 
hope this helps a little.....

…..Please remember that we tune each of the carburetor circuits based on throttle position and not RPM. We also go from the bottom to the top, because to varying degrees there is a culmination/overlap of mixtures from one circuit/position to the next one. If these overlaps were not present and correctly tuned for… you would experience flat spots or bogs and/or surges as you open the throttle.
Idle to about ¼ throttle opening is primarily controlled by the pilot circuit and this fuel/airflow continues all the way to WOT… and thus affects the whole jetting spectrum. This is one of the major reasons that you jet from the bottom to the top.

1/8 to about 3/8 is controlled by the slide valve cut away.
¼ to about ¾ is controlled by the needle jet and jet needle.
5/8 to WOT is controlled by the main jet.
Note how each circuit overlaps!

An important point to note is that if a particular circuit is either too rich or too lean… the amount of overlap can shift up/down, shrink/expand the range that it should normally control. Due to an engines design characteristics, rider driving technique and a multitude of other variables… a particular circuit may need to be richer/leaner than it would be in a different situation. Then an adjustment would have to be made on either side to make the transition smooth.
 
The toomey kit def comes with a 310, but I think they also say to move the needle clip down to #3 slot from the top. This should raise the needle and add more fuel at 1/4 throttle where the main/needle take over from the pilot jet.

This sounds like a lot of fuel (but maybe you need it). I know most people run 260-290 mains with the stock carb but it's still Toomey's pipe and you'd like to think they know what they are talking about. You can always email them as well.

tech@toomey.com
 
Prob the most solid way to tell if that is a lean sputter or a rich bog is to putt around at that throttle for a min or three and then cut it off. Don't let it return to idle, just kill the ignition. Check the plug. Is it black (rich) or lean (white)? Go from there.
 
i'd bet money on the needle needing adjusted

Agreed. The engines not getting the right amount of gas off of idle. The needle effects performance from off idle to something like 1/2-3/4 throttle

Put the clip on the needle to the middle notch and see if it makes a difference. This I also learned from experience and help from members on this forum.

Here is some good info on the needle from another post:

NEEDLE: The jet needle is the most important component in determining your carburetors jetting. The needle is broken into 3 main functions; Diameter, Length, Taper. These needle functions have a large effect on the carburetors jetting from ¼ to ¾ throttle. In the following paragraphs we will explain the needles functions and how to adjust them.

DIAMETER: The needle diameter controls the jetting just above the pilot jet, right as the engine begins to pull. On most engine combinations the needle diameter is felt in the ¼ throttle range. The setting of the needle diameter is crucial to both the engines low RPM power and reliability.

The jetting at ¼ throttle is adjusted by changing the diameter of the needle. On gold colored needles identified with the 3 stamped in letter I.D. system the last letter refers to the needle diameter size. By referencing the enclosed jetting chart you can verify your needles size, and be able to determine what needle size may be required for your specific situation. In many instances you can leave the taper and length settings the same (if they are correct) and adjust only the diameter. EXAMPLE: If you have a needle marked DGJ and change it for a needle marked DGK, you have effectively Leaned the jetting at the ¼ throttle position. Reference the enclosed jetting chart to clearly understand this adjustment.

When the needle diameter is Lean the machine will have a loss of low-end power. The engine will feel very zingy (like a 125cc engine). When an engine is in this condition and then put under a heavy load the engine becomes very susceptible to seizing.

When the needle diameter is Rich the machine will sputter at ¼ throttle and be hesitant to take the throttle. In extreme cases the engine can feel like the choke is on or the plug is fouling.

When the needle diameter jetting is set correctly the engine will accelerate evenly thru the first part of the power band. The proper diameter setting will provide maximum low RPM power and very ride able throttle response.

It is important to remember that even though the needle diameter is mainly responsible for the jetting at ¼ throttle there is some bleed effect. With experience this can easily be deciphered. An excellent way to pin point the feel of the needle diameter is test needles in your machine that have both the same taper and length but richer and leaner diameter settings. Try a needle of each setting in your machine for 10-15 minutes of riding and you will begin to understand specifically what throttle position your dealing with.

LENGTH: The needle length is determined by the clip position (grooves at top of needle) setting on the upper portion of the needle. On most needles there are 5 clip positions. The top clip position is referred to as #1 and is the Leanest setting. The clips are referred to in numerical order with the bottom position being #5, the Richest (refer to attached jetting chart illustration). The clip/length setting covers the largest percentage of jetting in your carburetor. With an emphasis at ½ throttle, the clip (length) setting will bleed both up and down to some degree to cover a wide portion of the midrange jetting.

When the clip/length setting is Lean the machine will be very zingy sounding and feel kind of similar to an 80cc or 125cc machine. Lean in the midrange will also rob power and cause the machine to run hot and seize easily.

When the clip/length setting is Rich the machine will have a lazy feeling in the midrange. Exhaust note will be a little flat sounding. In extreme cases of richness the engine will even sputter or kind of crap out in the midrange.

The safest way to set the clip position is to richen up the clip position setting until the machine loses a little power (feels lazy/unresponsive) then lean it back one position. Ideally you like to run the needle setting in either the 3rd or 4th clip position, if possible. The needle clip jetting is especially critical to your machines reliability because on average more time is spent in the midrange than any other part of the throttle. Most machines pull very hard in the midrange, putting quite a load on the engine. This makes a lean condition very detrimental to your reliability.

TAPER: The needle taper is the angle of the needle at its lower half. The taper works the transition between the midrange and full throttle/main jet (¾ throttle position). The taper is the least sensitive function of the needle. Changes in the taper have very mild subtle changes in the jetting. The taper also affects the main jet size your carburetor requires. A leaner needle taper will use a richer main jet than a comparable engine/carburetor combo with a richer needle taper.