Question about Yamaha Xv 250 Virago S Motorcycles

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Engine stumbles coming off the idle (1996 250 Virago). A preliminary twist of throttle overcomes the problem, but should not be necessary. This occurs even when in gear & moving.

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Several different factors can cause the stumble you talk about. It could be one thing or a combination of things. First buy a new pair of spark plugs and a new pair of spark plug caps. You can get NGK brand spark plug caps for about $5 each and they are the same caps Yamaha will charge $28 for. This should address any issues with poor idle or take off from electrical issues.
Next, an air leak or dirty carburetor could be the cause of a bad hesitation. There is a vacuum piston in the carburetor. If the diaphragm is stretched of damaged (cracks or holes) or if the actual sliding surface of the carburetor piston and piston cylinder surface is dirty or sticky you will have acceleration issues. Carefully unscrew the top if the carburetor and remove it noting the order of the spring and sealing o-rings. Gently peel off the diaphragm and pull the piston out. Clean the piston and the carburetor mating surfaces being careful not to get carburetor cleaning solution on the rubber parts. Inspect the rubber diaphragm for damage and replace the assembly if necessary(about $135). Consider removing the carburetor, disassembling it completely and shooting carburetor cleaner through and the jets and main body passageways.
Finally, age may be a factor on the intake manifold . Unbolt the manifold from the heads and carefully inspect the rubber boot that seals the carburetor to the manifold. Replace the manifold if damaged (about $90). When installing the manifold back on to the cycle use NEW o-rings to address any air leak issues between the heads and manifold. Be sure to inspect all the tubes and plastic T fittings for cracks or damage and replace any damaged parts..
Any one of the these items or the combination of all of them is probably the cause of your hesitation.

Posted on Apr 09, 2011

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