Rapid RPM change at 3/4 throttle

[Mraw]

Hi, I have a 2001 sporster with the 951, I have been having an issue with surging rpms at 3/4 throttle or higher, for example when going from idle to WOT it will quickly get to 7,000 but then surge back and fourth between 4,500 and 7,000 rpm for around 3 minutes until dying. The rave valves have just been cleaned. Any idea where to start?

 

[JeremyD615]

I’d start by looking for an air leak somewhere in the fuel system. The first places to check will be the fuel filter/separator, and the selector switch...

 

[Mraw]

Should I bypass the filter and switch and see if the issue returns?

 

[JeremyD615]

That’s fine to do for testing. If that gets rid of the problem, you’ll want to go through and find the problem though. Don’t leave it bypasses.

 

[Sportster-2001-951C-Stock]

I'm reaching here a little but it would be easy to clean the RAVE crankcase check valve and confirm it's working well.

Sounds more like a fuel system issue though, which can roast a piston.

 

[Mraw]

Thanks guys got it working, it was leaking in air through the fuel filter

 

[JeremyD615]

Glad you found it! It’s always nice when people come back and close a thread out with a solution...