dying on me at high speed

[jcducros]

The bike has supertrapp exhaust I jetted the carbs and it works fine all the way to 85 mph and then I have to milk it to 115 mph or it just start to sputter badly, too rich  too poor ????? any idea ??thanks for help

[Gear Jammer]

Maybe starving for fuel, as in a collapsing line at high demand?

[Scott from FL, now in Maine]

I also have Super Trapps on mine and have never had a problem. Since you have recently worked on the carbs, I suggest you check for kinks in the fuel line or tank vent. I also wonder what kind of airfilter you have in it? I have a K&N installed. Could the airflow be getting restricted? Check your plugs and see if it is running lean. The whole Super Trapp system is designed (if you have the discs installed) to increase air flow. Almost acts like a mini turbo in the fact that at higher rpms the discs at the end create low pressure zones that actually pull more exhaust from the system and draws more air in thru the intakes. All back pressure is gone with this system. Mine, according to the dyno actually gives me about a 6 HP increase. Last note, the Super Trapp website recommends between 8 to 11 disc installed on each side. I current have 11 installed.  

[Patrick]

Kinda, sorta sounds like fuel delivery issues.. Will backing off on the throttle a little immediately set the engine to running correctly??  I too would look at the fuel tank vent line,, its all too common for it to kink when installing the tank.. If you have an in-line fuel filter, I'd check that also..  It doesn't sound like a jetting problem unless you went kinda nutz with them.. These monsters tend to run a bit rich on the top end with the 100 jets, so a new exhaust shouldn't require much larger ones..

[Chrisj CMA]

The bike has supertrapp exhaust I jetted the carbs and it works fine all the way to 85 mph and then I have to milk it to 115 mph or it just start to sputter badly, too rich  too poor ????? any idea ??thanks for help

If you have a stock (OEM) petcock you should replace with a high flow valve to rule out fuel delivery problems.  See, the stock petcock at max flow is SO close to actual fuel need volume that any amount of flow being diminshed will effectively make your petcock the high speed jet and limit fuel flow down to below actual need.  You will be draining the float bowls faster than they can fill at high speeds........starve and then they fill and its ok, until you over draw again and starve again, and again

I bet thinking about it that way describes what is going on

[sandy]

In addition to Chris's note, at high speeds, the manifold vacuum drops. If there's any faults in the petcock vacuum line or the diaphragm in the petcock, you'll starve for fuel. Mine use to do that at 90+. I replaced the whole petcock and no more problems.

[Scott from FL, now in Maine]

If the petcock has troubles I agree with rebuild or replace, but I have the Super Trapps and have never had any trouble with the fuel flow from the standard petcock. It doesn't sound like an upgrade is needed, but possible a repair 

[Blackduck]

Check the colour of the spark plugs.
Loosen a plug from either side, nip them back up and take the bike for a spin.
Run it above the RPM it is missing at, can be in a lower gear to keep the speed down, shut the engine off at that RPM and coast to a stop. Pull the selected plugs and check the colour of the end of the plugs. Dark sooty is rich and white is lean.
As the air intake design on these causes them to run rich at higher RPM if you have increased the jet sizes the chances are it is running rich.
A simple fix without pulling the carbs is to remove the foam pad in the intake trac. If it improves the response it was rich and if it makes it worse then it is lean.
Cheers Steve