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Join Date: Jan 2011
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When you open the throttle, you ARE giving it gas, but it's the wrong kind of gas. Air is a gas, but it won't burn. What you desire is for the carb to mix the correct amount of COMBUSTIBLE gas the air that you allow into the engine to make it perform. If you understand the operation then it makes it easier to solve the problem. As you open the throttle and allow more air into the engine, several things happen at the same time.
With that being said; there were 3 TRX300's produced 97 - the TRX300 and the TRX300FW used a VE91C A carb and the TRX300EX used a QB02A A carb
I'm going to presume you do not have a 300EX as the EX carb had an accelerator pump to get you past the stumble inherent to the VE91 carb - the VE91 is a CV carb without an accelerator pump, so you need to figure out if the sputter is caused by being too rich or too lean then you can start addressing the cause.
With the CV carb - as you open the throttle the velocity of the air passing through the venturi slows and there is an accompanying drop in vacuum - it is the design of the CV carb to attempt to keep the velocity of air 'constant' - this is achieved by using the loss of vacuum to lower the slide to increase the velocity of the air passing through the venturi - consequently, as the slide lowers, the slide needle reduces the amount of fuel allowed into the air stream. If the slide falls too quickly, the fuel decreases rapidly and too little fuel is mixed with the air and the engine misfires due to too little fuel - this is usually accompanied by a backfire through intake. If the slide does not fall fast enough, the velocity of the air in the venturi slows and too much fuel is mixed with the air. The engine loses power and 'blubbers' until the mixture corrects itself and starts running properly again.
If you have a 300EX and it's sputtering just off idle, it is usually caused by a maladjusted accelerator pump linkage or a faulty check valve in the float bowl accelerator pump fuel passage.
There have been entire books written addressing the problems of each style of carb. Please consider what I have put forth here and reveal what kind of carb you are working with, what model TRX you have and what type of fuel you are using (brand and grade).