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Hello people smarter than myself, I've been having some issues with my carb the last couple times I have gone riding, when I stab the throttle cold or warm it bogs down bad and wants to die on me ,my quad is completely stock other than removal of the spark arrestor, my thought was maybe I needed to rejet because of the exhaust so I bought a main and pilot jet kit, I installed the #42 pilot and a #150 main and adjusted the air fuel screw to 2 1/4 turns from seat, I'm still having the same issue where it wants to die when hitting throttle hard, seems to have power and run as it should past 1/4 throttle, I have also tried going as far as 3 turns on air fuel screw with no difference is response, I'm also at sea level and have fresh gas hasn't been sitting, any ideas or advice would be much appreciated thank you in advance
 

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Well, you did not mention what you have for an air filter - changes to the intake affect function more than changes to the exhaust.

Fuel screw: it is for idle only it has no effect over 1/16 throttle - it has no specific setting - the initial setting is so it will run well enough to get the engine up to operating temperature - for proper adjustment you ride the vehicle for 15 to 20 minutes then bring it into the shop - connect an accurate tachometer, set a window fan in front of the quad, start the engine, set the desired idle speed, turn the fuel screw in by 1/8 turn increments pausing 5 to 7 seconds between adjustments, when the engine rpm drops by 50, turn the fuel screw out one full turn and it is done. No need to mess with it from this point on.

Understand the bog: bogging is caused by vacuum drop and the inability of air passing through the venturi of the carb getting mixed with sufficient fuel to support combustion. Now carburetors are stupid and don't care which direction the air is flowing for it to be mixed with fuel. When you stab the throttle open, the vacuum drops and air flow instantly comes to a standstill - because of the overlap of the valve timing, the intake valve begins to open while there is still pressure in the combustion chamber and a small amount of air flow backwards through the carb picking up fuel then as the piston travels downward, the fuel rich air is drawn back through the venturi again picking up fuel on its way to the combustion chamber. This fuel rich air is easier to ignite and the engine accelerates normally.

Several things can be done to attempt to eliminate the bog. The first and easiest is to raise the idle speed. The second requires changing the carb settings so the accelerator pump squirts fuel immediately upon throttle opening. The third is to assure the intake is sealed and the restriction through the air box is as designed. If modifications have been made to the air box, then the mechanic is responsible for changing the carburetor to compliment the changes to the intake. Typically, the pilot jet does not need to be changed and if changed no larger than a #40 should be needed (stock is #38). Raising the slide needle one notch changes the fuel mixture throughout the rpm range but is primarily responsible for mid range operation. The main jet does nothing until full throttle and can be any size required depending on the individual combination of exhaust and intake changes. (use of genuine Mikuni jets is recommended unless the carb is other than OEM).

Bog when cold is normal and the engine should not be run hard (no full throttle operation) until the engine is approx. 3/4 full normal operating temperature. BTW, use only 91 to 93 octane non-ethanol blended fuel. If alcohol blended fuel is used, then a #42 pilot jet may be used and it anybody's guess as to what size main jet will work. Also, if using ethanol diluted fuel, use 95 to 97 octane.

Go to work and good luck
 
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