Petcock Maybe Stupid ?

[paulbaker1954]

May sound a daft question but as I am still no further with solving my running issues I am turning to other possible causes

When I have the tank on the bench and open the fuel tap I get flow from only one outlet but if I block one outlet it comes out of the other and vice versa

Is this normal as I would have expected fuel to flow from both outlets pretty equally

This is a virtually new replacement petcock by the way. I have taken it apart and can’t figure out how the internal drilling’s go ie how it is supposed to work

Anyone got a spare tank on a bench they can test to see if this is normal?

[paulbaker1954]

Think I found the answer to my owne question on our sister US site - seems like its normal but I still can’t get my head around it

http://forums.sohc4.net/index.php?topic=111546.0

[Andrew-S]

Think I found the answer to my owne question on our sister US site - seems like its normal but I still can’t get my head around it

http/forums.sohc4.net/index.php?topic=111546.0

Interesting conundrum as I've rebuilt my CB750 K1's petrol tap and about to test it, but cant open your link - could you repost please?

[hairygit]

It works on the principal of filling the first pair of carbs, when they are full the float needles close the float valves, which has the same effect as blocking one outlet with your finger, then fuel flows out of the other outlet to fill the other pair of carbs. As the engine uses fuel, the tank obviously supplies far more fuel than the engine can use, so the carbs file up as dictated by the float levels, but there should always be sufficient fuel available for them. The only problems with the system occur when the flow from the tank is seriously compromised, bolcked fuel filter, blocked air hole in filler cap, creased or collapsing fuel pipes

Sent from my POT-LX1 using Tapatalk

[paulbaker1954]

Think I found the answer to my owne question on our sister US site - seems like its normal but I still can’t get my head around it

http/forums.sohc4.net/index.php?topic=111546.0

Interesting conundrum as I've rebuilt my CB750 K1's petrol tap and about to test it, but cant open your link - could you repost please?

Modified link should work ok now

[K2-K6]

Funny posts in that link 

When the tank is not connected and tap is opened then fuel running out of one pipe will cause a vacuum in the other outlet if the intake side of the tap is not significantly greater than one outlet.  Exactly the same principal of how the carb sucks fuel into the air stream only demonstrated in opposite fluids.

In reality the whole system us sized to make sure the volume can always fill the float chambers under maximum demand so not supply shortage happens.

The whole concept of a float chamber is to isolate it from tank and delivery pipes, all it has to do is have an excess supply that the float valves can regulate.

My favourite is the missing lead theory  stands to reason that fuel will go slower downhill without heavy lead added to it 

[paulbaker1954]

Funny posts in that link 

When the tank is not connected and tap is opened then fuel running out of one pipe will cause a vacuum in the other outlet if the intake side of the tap is not significantly greater than one outlet.  Exactly the same principal of how the carb sucks fuel into the air stream only demonstrated in opposite fluids.

In reality the whole system us sized to make sure the volume can always fill the float chambers under maximum demand so not supply shortage happens

The whole concept of a float chamber is to isolate it from tank and delivery pipes, all it has to do is have an excess supply that the float valves can regulate.

My favourite is the missing lead theory  stands to reason that fuel will go slower downhill without heavy lead added to it 

So I am  wondering if all my rough running issues are down to the  90 degreee nylon  elbows I put between the petcock and carb fuel lines (see other post http://www.sohc.co.uk/index.php/topic,20087.30.html)

What I am getting at is that by putting smaller bore connectors in the fuel lines I am getting fuel starvation in carbs 1 and 2 due to a flow imbalance

[Menno]

So... I have lots of fuel taps.
If I open one gas flows from both pipes.
Sometimes one a bit stronger than the other.

[deltarider]

So I am  wondering if all my rough running issues are down to the  90 degreee nylon  elbows I put between the petcock and carb fuel lines (see other post http://www.sohc.co.uk/index.php/topic,20087.30.html)
What I am getting at is that by putting smaller bore connectors in the fuel lines I am getting fuel starvation in carbs 1 and 2 due to a flow imbalance

First and most important: stick to the exact dimensions of the fuel lines that Honda fitted. It takes very little to hinder fuel flow, is my experience. Abstain from extra inline filters. Have a look at the filters that I have used. They all caused problems, sooner or sometimes much later (when you had completely forgotten you had fitted them!). Are you sure your nylon elbows are fuel resistent?

[K2-K6]

Certainly possible that altering flow will change this and dependant on size restrictions. 

Can't remember if you rigged some float height checks to your carbs?  If you have them then you could run it with them fitted and observe fuel level.

Generally petrol will get through most gaps as anything a bit iffy will give you a leak.  But if you restrict it below engine usage then at some point it will impair float bowl level.  It's usually seen when using higher rpm but letting it tickover would have the potential to let it recover.

That "vacuum" affect I've noted above,  could come into play if you've restricted ALL lines,  as if 3/4 are asking for fuel (depleted carb level)  they could in effect be switching off the 1/2 line by causing a more constant draw on the tap.

You're going to have to suck-it-and-see to prove or dispell it.

[paulbaker1954]

Certainly possible that altering flow will change this and dependant on size restrictions. 

Can't remember if you rigged some float height checks to your carbs?  If you have them then you could run it with them fitted and observe fuel level.

Generally petrol will get through most gaps as anything a bit iffy will give you a leak.  But if you restrict it below engine usage then at some point it will impair float bowl level.  It's usually seen when using higher rpm but letting it tickover would have the potential to let it recover.

That "vacuum" affect I've noted above,  could come into play if you've restricted ALL lines,  as if 3/4 are asking for fuel (depleted carb level)  they could in effect be switching off the 1/2 line by causing a more constant draw on the tap.

You're going to have to suck-it-and-see to prove or dispell it.

Agree will have to wait till I get head back and on again  and I didn’t check with float level (wish I had) as mechanic was convinced I had a valve issue.

Having now checked just about everything on this bike including ignition, pilot jets, idle circuits, float levels, HT leads and caps , valves for bend and head for flatness I am really running out of options !!!!

[paulbaker1954]

I bought some of this Paul.

It's almost the same as the OE piping but made from Nitrile.

Not been able to test it yet as the bikes nowhere near ready to run yet, however I'm sure others on here have bought the same pipe and found it works just fine.

https://www.ebay.co.uk/itm/Nitrile-Rubber-Smooth-Fuel-Tube-Petrol-Diesel-Oil-Line-Hose-Pipe-Tubing-NBR-1MTR/140693835989?ssPageName=STRK%3AMEBIDX%3AIT&var=440044001336&_trksid=p2057872.m2749.l2649

I went for some 5.4mm cotton braided hose as it has a thicker wall thickness than the nitrile stuff I have some of the nitrile but it’s quite thin wall and worried may be more subject to kinking. The overbraided stuff is similar wall thick to the HONDA OEM

Lost the fleabay link though !!