150cc running problem

[Frank Castle]

Originally Posted by Lefty

If the RPMS at IDLE are bounceing it is running really LEAN, you either have a AIR LEAK or the Carbs Fuel Mixture is way off.
So First check for any Air leaks take a Spray Bottle of Water and spray Indiviudal Areas, If the IDLE CHANGES you found a leak. Also check your Air Filter tubing for cracks and what not also you air box. If cracked tape them up etc..

If all that is good then adjust the Carbs Fuel Mixture
Lefty

Follow this procedure to tune the carb: Take your time 1/4 turn to much in either direction makes a big difference.


ADJUSTING YOUR FUEL RATIO MIXTURE:

YOU WANT THE HIGHEST RPMS OUT OF THE AIR RATIO MIXTURE SCREW:

Start your scoot and Get The Engine Nice and Hot about 5 minutes so that the Enricher IF it has one is no longer Allowing Extra Fuel to come in. Then do the following to fine tune the Fuel Ratio Mixture:

FUEL RATIO SCREW:

FIRST TRY RICHENNG THE FUEL MIXTURE FROM ITS CURRENT SETTING:


RICHEN THE FUEL RATIO MIXTURE:

1. Turn the Fuel Mixture Screw COUNTER CLOCKWISE 1/4 of a turn and wait 10 seconds to let the engine catch up with the new setting.
a. If the RPMS go up REPEAT #1 UNTIL the RPMS GO DOWN OR NO CHANGE(then go to b).
b. TURN the Fuel Ratio Mixture Screw CLOCKWISE 1/8 and that should be your highest Fuel Ratio Mixture setting—GO TO #3.

******If on the FIRST 1/4 TURN from the STARTING Position IN #1 ABOVE the RPMS GO DOWN OR NO CHANGE , turn the Fuel Ratio Mixture Screw Back the 1/4 turn to the Starting position and wait 10 seconds until the engine catches up -- GO TO #2 ******


LEAN THE FUEL RATIO MIXTURE:

2. Turn the Fuel Mixture Screw CLOCKWISE 1/4 of a turn and wait 10 seconds to let the engine catch up with the new setting.
a. If the RPMS go up REPEAT #2 UNTIL the RPMS GO DOWN OR NO CHANGE(then go to b).
b. TURN the Fuel Mixture Screw COUNTER CLOCKWISE 1/8 and that should be your highest Fuel Ratio Mixture setting—GO TO #3.



IF YOU GOT TO THIS POINT AND NOT INSTRUCTED TO GO TO #3 THAT MEANS THERE WAS NO CHANGE IN RPMS FROM DOING #1 or #2 ABOVE, IT IS TIME TO CLEAN THE CARB:

YOU NEED TO CLEAN YOUR PILOT JET AND PASSAGE AND AIR PASSAGES AND THEN START FROM #1 AGAIN.


IDLE SPEED SCREW:

The Idle Speed Screw on a Carb that are on most 4Ts you will find on the right side on the THROTTLE CONTROL WHEEL. It is the screw with a SPRING on it.

To Lower the IDLE you turn it COUNTER CLOCKWISE to Raise the IDLE you turn it CLOCKWISE.

3. If after adjusting your Fuel Ratio Mixture your idle is to fast Turn the IDLE SPEED SCREW COUNTER CLOCKWISE. For the 50s-150s they like to idle around 1500-1800rpms, for the 250s+ they like to idle from 1800-2000 rpms, pick the smoothest idle with the rear wheel not spinning ---GO TO #4.


TEST YOUR ADJUSTMENTS:

4. Now give the Throttle a QUICK twist and the RPMS should climb up quickly without hesitation or bogging and come down to where you set your Idle at---GO TO #5.

5. NOW take a ride and try it out, the Fuel Ratio mixture may need a tweak in either direction now that the motor has a load on it.

The tweak will be minor maybe a ¼ turn richer or leaner IF it acts up with a load---GO TO #6


6. When it acts up BACK OFF the throttle about ¼ of an INCH AND HOLD IT THERE:

a. If the motor speeds up it is LEAN you need to richen it up a little.

b. If the motor settles down and or stumbles and then settles down it is RICH you need to LEAN it out a little.

GO TO #5 AGAIN.



Problems with the IDLE:

1. Give the throttle a quick twist:

A. If the rpms drop below idle speed, then recovers (or stalls), it is RICH —Turn the Fuel Mixture Screw Clockwise ¼ turns at a time and go to #1.

B. If the rpms do not drop quickly to the idle speed but hang and drop slowly it is LEAN —Turn the Fuel Mixture Screw Counter Clockwise ¼ turns at a time and go to #1.

great info