RPM Flat Spot?

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Stevil25

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Ok so I know just about the basics when it comes to the mechanics of motorcycle engines, so im hoping i can get some good explanation and advice to this. I was wondering if its just me or if anyone else has the same problem with their bike. Some times I like to open up the throttle a little bit while out for a ride, as most of us do im sure, and it seems that there is a little bit of a dead (flat spot) in the rpms around 4500-5000 rpm ultimately not providing full power throughout the range but once you hit 6000 or so it takes off again providing a little bit of a jolt. Its not much but just slightly, and it leaves me to believe Im loosing a little bit of the power that could be produced. Is there a cure for this or am I just crazy and the only one that has the problem? Any help or comments needed and appreciated.
 
I don't have a Gen I bike, but have owned other carbureted Yamaha's with the EXUP valve. Two things...make sure your EXUP valve is properly adjusted and get a jet kit. These bikes are notorious for running lean from the factory so I suspect that it's very lean in that range and that's why you're noticing the lack of power at those RPMs.
 
Jetting

Wonderful info thanks.

Now you bring me to another question. The elevation here is about 4500 feet so if I do a jet kit on my bike how is that going to affect it with drastic increase and decrease of elevation. will the bike be affected or no?
 
Stevil25 said:
Wonderful info thanks.

Now you bring me to another question. The elevation here is about 4500 feet so if I do a jet kit on my bike how is that going to affect it with drastic increase and decrease of elevation. will the bike be affected or no?
Click to expand...

Well that is one of the drawbacks of carburetors...they have no way of automatically compensating for the thinner air at higher altitudes like EFI does. You should get your bike tuned and jetted for your altitude and then just deal with the elevation changes as they come. If you get a quality jet kit like Dale Walker's or Ivan's, one of the advantages is that you'll also get access to their knowledge. Either one should be able to tell you how to properly set up the carbs for your altitude.

As for the EXUP valve, everything you ever wanted to know is on Pat's page:

http://www.cartestsoftware.com/fz1/exupmaintenance.html
 
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