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Old 01-30-2005, 04:05 PM   #1
bluex6rider
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how to tune a 4-stroke carb?

i have a 4 stroke pb and am having trouble with getting to run right. it starts up but i can't give it full throttle from a complete stop , i would have to ease my way up to full throttle, when i would give it full throttle from a complete stop the engine will just die out. there are only 2 screws available to adjust one of them is the idle screw and the other one seems like it does nothing, i've tried to turn it all the way in and it acts the same so i turned it all the way out and it still acts the same..........can anyone please help me out
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Old 01-30-2005, 04:52 PM   #2
smn1
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Tuning of the engine at idle and low speeds is accomplished by adjusting the idle mixture screw (555585) or changing the size of the pilot jet, also called slow jet. The jet size or diameter in millimeters is stamped on the jet (32 = .32mm orifice). The idle mixture screw is an air bleed adjustment, so closing the screw or turning it clockwise will richen the fuel mixture, and opening the screw or turning it counterclockwise will lean the fuel mixture.

To adjust the idle mixture screw proceed as follows. Turn the idle mixture screw in until it lightly seats or stops. Back the screw out the specified number of turns. Warm the engine and set the Idle Speed screw slightly higher than the desired idle rpm. Turn the idle mixture screw in or out to obtain the highest rpm. Turn the idle speed screw to the desired idle rpm. A slightly rich idle mixture is usually better for acceleration.

If a smooth idle cannot be obtained with the idle mixture screw between 1/4 - 2 1/4 turns out from closed, a different size pilot jet may be needed. The proper size pilot jet will allow for smooth acceleration from an idle and steady engine speed up to / throttle opening.

Mechanical Idle SPEED Adjustments

The overall idle speed is set using the Idle speed screw (555586). Movement of this screw clockwise will raise the slide, effectively raising idle speed. Counterclockwise movement of the screw will lower idle speed. This adjustment will affect the overall idle speed of the engine and with adjustments of the mixing screw, will control idle and initial responsiveness/acceleration of the engine.

Midrange / Part Throttle

The jet needle (555602) primarily controls fuel flow between 1/4 and 3/4 throttle opening. The jet needle has five notches and a C-clip on the top of it. To richen the part throttle operation, move the clip to the next lower notch. To lean the part throttle operation, move the clip to the next higher position. The highest notch (farthest from the tip) is considered the first position. Needle taper reference letters are stamped on the needle for identification. This adjustment is inside the carb. You have to take the top of the carb off and pull the needle jet out. It has a c-clip that you adjust by moving up or down. Mine came in the middle of the 5 adjustment settings.

Good luck

Last edited by smn1; 01-30-2005 at 04:55 PM.
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Old 01-30-2005, 05:20 PM   #3
bluex6rider
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Quote:
Originally Posted by smn1
Tuning of the engine at idle and low speeds is accomplished by adjusting the idle mixture screw (555585) or changing the size of the pilot jet, also called slow jet. The jet size or diameter in millimeters is stamped on the jet (32 = .32mm orifice). The idle mixture screw is an air bleed adjustment, so closing the screw or turning it clockwise will richen the fuel mixture, and opening the screw or turning it counterclockwise will lean the fuel mixture.

To adjust the idle mixture screw proceed as follows. Turn the idle mixture screw in until it lightly seats or stops. Back the screw out the specified number of turns. Warm the engine and set the Idle Speed screw slightly higher than the desired idle rpm. Turn the idle mixture screw in or out to obtain the highest rpm. Turn the idle speed screw to the desired idle rpm. A slightly rich idle mixture is usually better for acceleration.

If a smooth idle cannot be obtained with the idle mixture screw between 1/4 - 2 1/4 turns out from closed, a different size pilot jet may be needed. The proper size pilot jet will allow for smooth acceleration from an idle and steady engine speed up to / throttle opening.

Mechanical Idle SPEED Adjustments

The overall idle speed is set using the Idle speed screw (555586). Movement of this screw clockwise will raise the slide, effectively raising idle speed. Counterclockwise movement of the screw will lower idle speed. This adjustment will affect the overall idle speed of the engine and with adjustments of the mixing screw, will control idle and initial responsiveness/acceleration of the engine.

Midrange / Part Throttle

The jet needle (555602) primarily controls fuel flow between 1/4 and 3/4 throttle opening. The jet needle has five notches and a C-clip on the top of it. To richen the part throttle operation, move the clip to the next lower notch. To lean the part throttle operation, move the clip to the next higher position. The highest notch (farthest from the tip) is considered the first position. Needle taper reference letters are stamped on the needle for identification. This adjustment is inside the carb. You have to take the top of the carb off and pull the needle jet out. It has a c-clip that you adjust by moving up or down. Mine came in the middle of the 5 adjustment settings.

Good luck
this sounds really technical. did you get it out of a manual? i really appreciate your help in this matter

Last edited by bluex6rider; 01-30-2005 at 08:00 PM.
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