Ideas on where to start.

2008 S40. Never really did highway cruising but I have latley and the bikes not acting right. 0-70 bike seems good to go, no issues at all. The only issue I've seen is it won't start with the choke out at all. The choke has to be pushed in or "off" to start the bike. Outside of that, accelerates great, runs great.

75ish to 80 it starts chugging on the highway, lunging almost. It's so bad that I have to either get off the highway or off to the side. If I slow down its great. Sometimes if there is a strong headwind, same thing even at 70 mph. I normally pull in the clutch, go to neutral and cost to a stop. Today it was doing it on the highway and I attempted to "ride it out" as I got off the highway and it was backfiring like crazy.

Mods:
Cone filter - K&N RC-1250

155 main

Can't remember the other jet size.

Exhaust - VooDoo Industries VC403 Chrome Universal Cafe Style Exhaust Pipe

Aftermarket Petcock - 5LP-24500-01-00 Fuel Valve Petcock Assembly Replacement Compatible with YAMAHA 2005,2004,2003,2002,2001 YFM660R RAPTOR 660# 5LP-24500-01-00


Location:
Las Vegas

No, aftermarket.  Updated post, sorry should have put that in there.  

Never ran it at highway spoeds with the original petcock as it was faulty. I'll have to possibly try a new petcock. Do you think that specifically could be an issue ast those speeds and those speeds only?

5-6 months of 60 mph or under with the current setup, no problems. Never did highway driving.

Yeah the 'chug' is a fuel problem.
1st cause has been eliminated by upgrading to the raptor petcock.

Do you have a fuel filter on it?  That's the 2nd likely cause.

Did you remove the plastic shield from the new petcock when you installed it?

The new petcock has a screen... check that and there's a screen above the float valve, check that too.

Last thing I can think of is the float level.

It could also be a clogged tank vent. Some vent in the cap, some vent via tube to a canister.

Hey Brandon, what did you find?

You can check for sufficient fuel flow by removing your float bowl, placing a suitable container under the carb, and turning on your petcock.  You need to determine how much fuel the system will flow in one-minute.  

You need about 6 ounces per minute to support 35 horsepower.

You want to perform this test through the normal flow circuit.  In other words, through the petcock, fuel hose, and needle & seat.  To verify that the tank is properly vented, your gas cap must be installed while you are doing the test.  If it doesn't flow at least 6 ounces per minute, something is wrong.

Your carb will look like this picture with the float bowl removed.  See the little tang circled in yellow.  That tang adjusts float drop.  If you aren't flowing at least 6 ounces per minute, and none of the components are obstructed, try adjusting your float drop to allow the needle to open a little more.  See if that increases fuel flow.  Make sure the system will deliver at least 6 ounces per minute.

Good luck.

Fine line between hugging it and rubbing it.