Fuel starvation

[Repsolnc30]

Ok thanks will change position of larger flap and see if that works

[arsey30]

I would have suggested the vacuum hose to the tap, or the tap diaphragm.
However, as it runs well on the dyno, more like air flow. [Unless a dummy tank was used to allow easy access to the carbs]
The rubber flap may be lifting to obscure the air box intake, apart from that it would not matter how it was fitted as regards to poor running at 100 mph.

[Neosophist]

Have you done the fuel tap mod? Common problem at high revs is for the carbs to run out of fuel, which to me describes your problem...that or the air box set up, but I used to notice it at around 60-70mph not 100 when I messed with my scoop etc

I think "common problem" it is not.

The rubber flap keeps the warm air from the air box [less dense]
Fuel starvation occurs when flat out for a while, not at 100mph, the standard tap delivers enough fuel for road use, the HRC mod can give rise to fuel leaking into the engine.

I agree with what arsey30 has said.

A lot of peopel seem to think "HRC" is synonymous with performance increase.

The vaccum tap serves as a safety device, if you bin the bike fuel will not continue to leak out indefinatly if the engine isnt running.

If one of your float valves fail the tank wont drain all over the floor.

I have ridden an NC30 jetted to 118/120 flat out for a 50 mile stretch without any sign of fuel starvation.

Most high rpm issues are caused by vaccum pipe failing, removing the diaphram obviosuly fixes this too in a roundabout way.

The diaphram does block a small amount of the tap but wth standard jetting you shouldnt have any issues.

Now if you look at the F3 setup its running an open-air tray, difference rods and camshafts and pistons and what not along with 145+ main jets.

Honda obviously had issues with this setup so needed to bypass the vaccum tap. For a roadbike in good working order I dont see any reason to do it

the rubber flap seems to make most difference as already mentioned, especially on a stock setup these bikes suffer a lot from disurbing the air-flow.

[Icemaestro]

I agree absolutely that it makes things worse - a bike I bought had it done and I changed it back as I would occasionally forget to turn it off and one of the float valves didn't seat properly... It was simply something I have been told several times from people who raced these that at extended periods of high rpm and load - I can't say I know anyone who sits at 100mph that isn't on a track hence my comment. Good to know it only applies to the full hrc setup if you plan to race.

Yep not many people get to test it, but with a stock jetted bike you can ride up and down the autobahn flat out until you run out of fuel without any issues with the standard tap setup. :)

Unless your running a race setup wtih big jets / open carbs I wouldnt recommend it, and even then install a dry-break when not using the bike.