TRX250R.ORG
Workshop => Carburetor, Intake, and Exhaust => Topic started by: goatracer on October 16, 2016, 06:32:01 PM
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im a bit rich at 1/4 throttle right now my current set up is a 370 race gas with a 38 air striker 58 pilot dgh second from full rich and a 180 main what cn i change to lean 1/4 throttle just a bit
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That seems like a huge pilot. You could also drop the needle
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i did lower the needle one spot today it was full rich, this did help some
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Are you sure the problem you are having is occurring when the slide is 1/4 open or when the throttle lever has been moved 1/4 of its total travel. In order to determine what circuit is responsible for your problem, you have to accurately determine where the slide is positioned when the problem is occurring.
Where is your idle stop adjusting screw set? If it is turned in all of the way and the air screw is 1.5 to 2 turns out there is a good chance that the pilot jet is too large. I usually end up with a 45 to 52 pilot in similar setups. If the idle stop screw is not turned in all of the way and the air screw is somewhere between 1.5 to 2 turns out I would install a DGJ or DGK needle. The diameter of the straight portion of the needle and slide cut away is what controls the fuel flow between the needle jet and needle from zero to almost half throttle. Moving the clip a position will not change the mixture at 1/4 throttle!!!!!!!!!!! Moving the clip on the needle does not change the mixture until the throttle is open enough for the taper to cause a change in fuel flow. Put a mark on your needle where the taper starts. Remove the carb from the reed. Open the throttle and observe when the mark becomes visible. This is the throttle position where moving the clip will change the mixture.
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idle speed screw is almost all the way in, it does not seem to like a pilot less than 55
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That seems to be the way pwk end up with the idle screw
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my elevation is around 700 foot above sea level
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Are you sure the problem you are having is occurring when the slide is 1/4 open or when the throttle lever has been moved 1/4 of its total travel. I order to determine what circuit is responsible for your problem, you have to accurately determine where the slide is positioned when the problem is occurring.
Where is your idle stop adjusting screw set? If it is turned in all of the way and the air screw is 1.5 to 2 turns out there is a good chance that the pilot jet is too large. I usually end up with a 45 to 52 pilot in similar setups. If the idle stop screw is not turned in all of the way and the air screw is somewhere between 1.5 to 2 turns out I would install a DGJ or DGK needle. The diameter of the straight portion of the needle and slide cut away is what controls the fuel flow between the needle jet and needle from zero to almost half throttle. Moving the clip a position will not change the mixture at 1/4 throttle!!!!!!!!!!! Moving the clip on the needle does not change the mixture until the throttle is open enough for the taper to cause a change in fuel flow. Put a mark on your needle where the taper starts. Remove the carb from the reed. Open the throttle and observe when the mark becomes visible. This is the throttle position where moving the clip will change the mixture.
Thanks for your input. Didn't realize needle wouldn't change at 1/4 throttle. I would listen to Jerry. He is far more knowledgeable than me
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Have pressure tested you motor. To see if you have air leak.
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no i have not
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my elevation is around 700 foot above sea level
The pilot jet for 700 ft will be good for sea level to about 3000 ft.
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idle speed screw is almost all the way in, it does not seem to like a pilot less than 55
What running symptoms do you experience when you go leaner than a 55 pilot jet
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very hard starting and it does not pull as well
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That seems to be the way pwk end up with the idle screw
If the slide is open more than about 2mm it will usually take a large pilot jet to give the right idle speed.
Most of these carburetors need the slide to be open 1 to 2 mm to allow the proper air flow to make the engine idle at the right RPM when the idle mixture is correct.
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very hard starting and it does not pull as well
Does activating the choke button improve starting when you go leaner on the pilot?
Does going leaner on the pilot cause the engine to have a hesitation when suddenly opening the throttle
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choking helps but very hard starrting still even after being ridden, no hesitation just not as strong
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Are you sure the problem you are having is occurring when the slide is 1/4 open or when the throttle lever has been moved 1/4 of its total travel. In order to determine what circuit is responsible for your problem, you have to accurately determine where the slide is positioned when the problem is occurring.
Where is your idle stop adjusting screw set? If it is turned in all of the way and the air screw is 1.5 to 2 turns out there is a good chance that the pilot jet is too large. I usually end up with a 45 to 52 pilot in similar setups. If the idle stop screw is not turned in all of the way and the air screw is somewhere between 1.5 to 2 turns out I would install a DGJ or DGK needle. The diameter of the straight portion of the needle and slide cut away is what controls the fuel flow between the needle jet and needle from zero to almost half throttle. Moving the clip a position will not change the mixture at 1/4 throttle!!!!!!!!!!! Moving the clip on the needle does not change the mixture until the throttle is open enough for the taper to cause a change in fuel flow. Put a mark on your needle where the taper starts. Remove the carb from the reed. Open the throttle and observe when the mark becomes visible. This is the throttle position where moving the clip will change the mixture.
Jerry, how much difference is a #6 slide vs a #7... If someone were running a G diameter needle with a #7 slide with proper AF mixture, and then went to a #6 slide how much would the needle diameter need to increase to compensate for the change? H or J diameter? I noticed slide selection is rarely discussed in people's mention of jetting. My understanding is you typically use the leaner slides for large bore applications like a cr500, when should someone consider a slide change and what do you recommend for 250r's? Thanks!
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Jerry, how much difference is a #6 slide vs a #7... If someone were running a G diameter needle with a #7 slide with proper AF mixture, and then went to a #6 slide how much would the needle diameter need to increase to compensate for the change? H or J diameter? I noticed slide selection is rarely discussed in people's mention of jetting. My understanding is you typically use the leaner slides for large bore applications like a cr500, when should someone consider a slide change and what do you recommend for 250r's? Thanks!
If you have the wrong slide you cannot compensate by changing the diameter of the straight portion of the needle just like you cannot change the pilot to compensate for having the wrong needle diameter or slide. All the fuel circuits overlap each other but, each fuel circuit has a primary throttle position that it has the largest influence on fuel control.
The fuel flow area between the needle and needle jet does not change from closed throttle to the point where the taper starts to change the fuel flow area. The taper on the needle starts to change the fuel flow area at around 1/2 throttle opening. The cutaway on the slide changes the angle that the air flows over the needle jet shroud. At small throttle openings a slide with a large number directs the air more downward as the air passes over the needle jet shroud, causing less suction and thus a leaner mixture than a slide with a smaller cutaway with the same needle diameter. The effect of the slide cutaway is greatest at about 1/8 to 1/4 throttle and has diminished to zero at around 1/2 throttle.
Understanding what fuel circuits are working and the throttle position where each fuel circuit has the heaviest influence is the key to being able to tune like a veteran tuner. Without this understanding one is wasting their time trying to tune a carb.
The pilot jet and air screw have the heaviest influence upon the idle mixture after all of the surfaces in the crankcase have become saturated with fuel and oil and have stabilized so that air fuel ratio from the carburetor passes through the crankcase to the combustion chamber unchanged. It is not uncommon for this to take 10 seconds or more when the engine is returning to an idle after a few seconds of partial or full throttle. Not understanding this phenomena is one of the main reasons guys should not waste to much time trying to make a two stroke idle like a four stroke. A four stroke only has the intake port surface area that has to saturate and stabilize before the air fuel ratio from the carburetor passes through the intake port unchanged.