Hi iv heard alot about the HRC fuel tap mod and how it can leak fuel into carbs and fuck up the engine etc but whats it actually for?

Im building a race bike and is it worth doing this mod? I was planning on putting a dry break fuel line coupler thing on anyway so is it worth a go?




o before you say i tried a search and didnt find much

You can convert the fuel tap to full flow, described here:

http://www.akhara.com/nc30/fueltapmod/index.html" onclick="window.open(this.href);return false;

This site has some good info for the NC30.

I belive it allows a better flow of fuel to the carbs, i did it to my trackbike but cant say i noticed any difference or had any problems with it, even forgot to turn the tap off after a trackday once and it sat like it for a month before i noticed . Didnt do no damage tho and started on the button.

The only reason for it is when you run with no filter (nc30 and nc35 hrc setup) there's not enough vacuum to open the std fuel tap always.

The basic principle around it is that with a full F3 bike, the vacuum wouldn't be enough to fuel the bike and it would suffer from starvation with the monster jets in the carbs and last of air restriction from running no air filter. For the very same reason I did it to my track-bike when I had the ram-air fitted and a fuel pump. As long as you split the dry break after every session then you'll be sweet.

To answer the bit about leaking fuel is more to do with the floats not cutting off the fuel leading to the fuel running down the cylinders and into the engine-oil. The petrol wreaks havock with engine internals that should be lubed by the oil and can eventually kill your motor.

ok so I guess you need it for a ram air setup? think il do it and put the dry break in then its done and I dont need to worry about it in the future

Cheers for the help guys

When I took my bike to the Dyno Shop, (Ahem.. Not now boys hey?) We found that the bike produced more power with bigger jets. (And the Slide Air-Bleed holes drilled to 2.5mm) We kept on increasing the jets by one size until we noticed the power starting to level off or drop..
10 sizes bigger now, and the power was still getting stronger in the bottom of the revs, 3'000-8'500rpm, but towards the top the power bogged down from starvation of fuel. (For some reason?) I did the HRC Tap mod, and converted the tap to gravity fed so there is an equal and constant feed to the carbs and hey presto, the power curve returned to a good shape. Really made a difference to the top end according to the Dyno. Bike pulls like a train now from 3'000rpm right upto about 13'000rpm where the power starts to slope away.


So to summarise, the HRC Mod converts the tap from vacuum fed, to constant gravity fed so you dont get any fuel starvation at any rpm. Not really necassary on a road bike at all, even on a track bike, unless your messing with the carbs a lot, i dont see why you would have to do it. but it is good advice to do it if your getting serious with the machine. Just remember to turn the tap off when not in use. I regularly forget to turn mine off and I cringe everytime I hit that starter button the next time.. LOL

Spike16 wrote:ok so I guess you need it for a ram air setup? think il do it and put the dry break in then its done and I dont need to worry about it in the future

Cheers for the help guys

Go the fuel pump route for ram air spike, wont have to worry about it then.

Drunkn Munky wrote:

Spike16 wrote:ok so I guess you need it for a ram air setup? think il do it and put the dry break in then its done and I dont need to worry about it in the future

Cheers for the help guys

Go the fuel pump route for ram air spike, wont have to worry about it then.

I did both. Didn't want to suffer from any sort of fueling starvation at 14,000rpm

viper_biker wrote:

Drunkn Munky wrote:

Spike16 wrote:ok so I guess you need it for a ram air setup? think il do it and put the dry break in then its done and I dont need to worry about it in the future

Cheers for the help guys

Go the fuel pump route for ram air spike, wont have to worry about it then.

I did both. Didn't want to suffer from any sort of fueling starvation at 14,000rpm

Yup, if you use a fuel pump, then do the hrc tap mod. Pumps work by intermittently pushing fuel through the line (and hence intermittently blocking it!), you can still run into issues if you rely on vacuum operation of the fuel diaphragm.