Fuel tap problems

[dicky]

Hate to be a pain, but which one is the inlet manifold hose?
Appreciate the quick responses to

I don't understand your question, so here is the step by step guide.
There are two inlet manifolds, alloy castings, between the cylinder head and the carburetors.
These bolt on the to the cylinder head and are connected to the carburetors with rubber sleeves.
Each of these manifolds has a small port exiting to one side to which is attached a rubber hose, one manifold hose goes to the fuel pump and the other goes to the fuel tap.
If you replace the original fuel tap with a 'normal' tap then you need to block port on the manifold so that air is not sucked in bypassing the carburetor. That would be bad.
It should be the left manifold, but you should trace the hoses to make sure they haven't been swapped at some time.

[kenbev]

Dicky, replaced my fuel tap with on/off/res and blocked off vacuum hose then connected fuel line directly to the carbies. My question is should I be going through the fuel pump. Bike starts and runs well as is but I just want to get it clear in my own mind. cheers. Kenbev.

[dicky]

Yes, it should run via the pump.
The bottom of the tank is lower than the inlet to the carbs, so without the pump you'll run out of fuel sooner than you think.

[kenbev]

Once again Mate many thanks for the answer. Happy new year. Kenbev.

[DreadmondDross]

Hi Guys,
New to the forum and new to bikes in general.

When you guys are talking about having problems with the Pet Cock leaking you mean leaking from around the surround rather than leaking through to the fuel Pump unwantedly?

I've made assumptions 3 stages on the Tap that they are
ON (ON - Activated by the vacuum pipe from the carb)
RES (RESERVE - Also Vacuum activated, assume just a lower pipe in the tank)
PRI (PRIME - I assume this allows Petrol to run without any vacuum activator)

[HolerTogni]

Hi DreadmondDross!

First a heartily welcome to the forum - have fun here and in the real life!

Then to your question:
The typical leaking of the fuel tap discussed here many times is the lurking of fuel through the "closed" fuel tap into the float chambers of the carburettors and - in the worst case - further on into the cylinder, where the fuel can (will) cause severe damage if the engine is started.

"Closed" because there is no closed position of the fuel tap and the fuel is lurking by the not so tight seals that should prevent exactly this.

That leads me to the assumptions you made on the positions of the fuel tap - they're all correct.

Welcoming and answering greets from Munich!

PS: You (already) own a TRX? As your first bike?
In this case: Congratulations!
And hopefully you get accustomed to her character and like (love!) it.

[dicky]

As already stated, the tap leaks through the internal diaphragm, leading to filling of the float bowls, and if they don't seal correctly, then filling the cylinder with fuel and possibly causing catastrophic damage due to hydraulic lock when the starter button is next pressed. Bent con rods, bent crank, cracked heads. Not good.
The tap can also leak around the outlet spigot, as this is glued in place and sideways pressure on the outlet can cause it to break free and rotate, which at first sight looks like a useful thing, but then it begins to leak. Not so useful.
Replace the entire tap assembly with one from a 98 R1 (5JJ) and then replace the hose connection to the fuel pump with a much longer hose that coils around under the tap, then you can lift the fuel tank back on the pivot bolt without having to disconnect the hose.

[DreadmondDross]

Thanks for the replies and welcome guys I don't think I have a problem with it yet but sounds like something worth changing before it does become a problem. Is the R1 tap a straight swap?

I know a TRX maybe isn't the obvious choice for a starter bike lol my brother has a 125 we are riding about on while waiting on covid to piss off and we get the test, the theory keeps getting pushed back. The TRX was my dads, unfortunately he dropped it about 10 or so years ago and never got round to fixing the front fairing and has sat in the shed ever since. Was having trouble running smooth or even staying running at idle and thought maybe it was fuel starved, replacement spark plugs on the way to rule that out at the minute.

[dicky]

The R1 tap bolts straight on. It is a normal On/Res/Off tap, not vacuum operated, so you will need to block the vacuum hose that is connected to the original tap.
For the other problems you described, check that the vacuum hose is actually connected, both ends. There is a second vacuum line that runs to the fuel pump. Both are connected at the inlet manifold, there is a spigot on the aluminium inlet adaptor. One one the left goes to the fuel tap, one on the right goes to the fuel pump.
There is also a small plastic cover on the side of the carb that can crack and cause an air leak. You can see the one on the RHS easily.
Other than that, normal aging will perish the rubber boots on the carbs and lead to cracks and air leaks.
A can of aerostart can help to find air leaks. Get the bike running then squirt a bit on the inlet manifold boots. If the revs pick up you probably have a leak.

[CapnStubing]

I've gone with this one..
https://www.ebay.com/itm/800659035317?_ ... BMtP20v6Ro