Bike wont idle stalls when i stop. if i adjust the idle screw to idle properly then once i start riding and let off the throttle the rpms stay at about 3000 to 4000 like i have cruise control on. what can i do?

Typical for any carburetor is 1 1/4 to 1 1/2 turns (out). These are just rough settings to get the saw running. Remove chain, turn idle throttle speed screw in to increase idle rpms so its less likely to stall. Follow mfg instructions for starting.

Once running, adjust low speed mix and allow a couple minutes to warm. Then re-adjust low speed and lower idle rpms by turning out idle throttle speed screw. Then with throttle wide open adjust high speed mix. If saw hesitates from idle to full throttle, open low speed mix 1/8 turn and readjust high speed mix.

If saw doesn't fire in 3 or 4 pulls remove plug. If plug is dry no fuel, if wet either no spark or idle mix to rich (or fuel metering may be fouled).

possible cause could be that the idle mixture adjustment for the carbys is out
find the adjuster screw and with the motor stopped turn all the way in then turn back out 1 and 1/2 turns start the engine and using the throttle to maintain engine running adjust each screw until the throttle is no longer needed
at that point turn one screw at a time in until the rpms slow then count the turns out until the rpms again slow , the turn in half that number of turns
at that point the carby is tuned for that cylinder
repeat for the other cylinder
failing that take it to an accredited bike shop and have it adjusted professionally

People this is a scooter. The problem is that your idle screw on the Carb needs adjustment. The idle screw can be adjusted with a Philips screw driver. Follow your throttle cable to the carb. You'll see a screw that pushes a pulley down raising your rpms. This will lower your idle causing the rpms to drop and since your scooter transmission is propelled my higher RPMs the bike will stop thrusting you forward when you stop at red lights.

If this is a new bike take it back to the dealer and have them properly set it up.
Options:
Sometimes a clogged air filter will cause the fuel/air mixture to become to rich and the bike will stall. Remove the filter and air blast it clean then wash wash in solvent/gasoline then let dry. Apply a very light oil to the filter to keep dirt out, then re-assemble.
Sometimes filters are in-expensive so just replace with new.
You also have a slide stop screw on the carburetor. This can be turned in about 1/8th of a turn to increase the idle speed.
Also: The throttle cable has adjustable ends both at the twist hand throttle and at the bottom where it goes into the carburetor. Vibrations may have loosened the adjustment and you may be able to re-secure the cable adjusters in the correct position for proper idle speed.
Best wishes,
TF

Do you have a vacuum comparison guage? You need some kind of guage setup to work on the TB sync.

Here is what I would do:
-perform a valve clearance check/adjustment to ensure everything is in spec. (this does make a difference!)
-Ride bike for 10-15 minutes, make sure it is fully warmed up.
-connect your vacuum guages to each throttle body.
-ensure that there is throttle cable slack on each throttle body. You don't want the cables holding the throttle plates open at this stage.
-set the brass air screws out equal turns on each side. Start with one and a half turns from bottomed.
-start engine (it may not want to idle, so open brass screws another half turn till it idles)and check vacuum guages.... see how far out things are at this stage.
-adjust throttle stop screw(s) so that each throttle body is set-up exactly the same.
-Once the throttle bodies are adjusted so that the vacuum is exactly the same at idle, start to remove slack from the throttle cables so that vacuum stays the same on each side as the throttle is opened.
-above all, you want the throttle plates to rest on the stops at idle and the cables adjusted with enough slack to allow this to happen. DO NOT tighten the cables too much as this causes the throttle plates to "bounce" at idle and wears out the throttle plate shaft bores quickly.

I think that about covers it, Post back if you have questions.

1 turn out is approximate setting fo H and L screws...once running adjust H screw so that it is just rich at full throttle (4 stroking then 2 stroking with out changing screw) once thats right adjust L screw at idle till it starts to pick up speed then just back off 1/8 of turn ....then you can adjust tapered screw to nice idle....if this fails you have carby problem

Hi,

Thanks for writing to Fixya.com.

I would check idle adjustment first. There are two idle controls on our cars, so it's not as straight forward as you'd think. There is the base idle (controlled by the screw) and the idle air control valve, controlled by the computer. This computer controlled value is used sparingly when needed. Mostly the car relies on the idle screw control. If this is set too low however, the computer will take over, and you'll think you have idle set correctly, until you let rpms drop from 2,000+ to idle, it will stall, or almost stall.

Adjust the idle screw up until idle raises to 1,000 rpms, then adjust it back down until you get to 850, but no more. If you adjust it more, the idle will stay at 850 because the computer controlled idle takes over. A lot of people (me included) will keep turning the screw all the way down, thinking everything is fine. Don't do it. Stop adjusting once you hit 850 rpms with a warm motor.

This is the easiest, quickest thing to check, so do it first before trying anything else.

Thanks for contacting Fixya and please accept the solution if it has helped you.

those are the throttle adjustment screws H is high L is Low for the air mixture of the idle.