I start her up and all I hear is a high pitch whistling/hissing noise. Mainly from the front cylinder! Help ...

no fuel line leaking

 

More info. What year? sounds like a possible vaccume leak somewhere

 

2001 sporster. Its a high pitch like whistling noise thru my baffle when it is running. But when I take the spark plugs out to turn the motor over, there is no sound like that at all???

 

Coming from the exhaust? Maybe the lifter is stuck and the valve is not closing all the way.

You may have also bent a valve and it is not sealing now.

Did you replace the heads or use the 883 heads? Your compression ratio may be way too high if you used the small chambered 883 heads without modifying them... could result in a blown head gasket. This can sound like a pulsing whistle. What head gaskets did you use?

 

Tell us more and help us to help you. Have you done the 1200 conversion recently? Is this happening just after you completed the build?

Frankly a whistle sounds more to me like a leaking head gasket. Is there any trace of oil around the head/cylinder join?