Fuel tap

[SDN]

Since I ran the bike out of fuel on reserve I have had some problems starting it, I can be cranking away for ages with the odd pop or bang, but it doesn't stink of fuel like it is flooded

it starts first off and runs fine on remote tank, but when I connect it to the tank I am really having to crank it.

It made no difference undoing the filler cap so I don't think it is the breather

I have tried a spare fuel pump which I tested and know is good - same.

In line fuel filter is good recently bought a new one

Which leaves me with the tap - anyone got any ideas?

One thing that I have noticed is that the Fuel filter which is clear doesn't seem that full of fuel and nothing seems to be happening when the bike is running, I thought I would see fuel moving

Some of you guys have mentioned running a conventional on / off / reserve tap - what type / model do you use?

Once running the bike runs fine ??? its doing my head in

[Rich]

doesn't have a fuel pump, the square alloy block with the pipes going into it is a vacuum operated cut off valve.

I think if you take the fuel tap to bits you can reconfigure it to be on/off/reserve.

I would try undoing the drain plugs on the float chambers and seeing what comes out, may be a case of jets blocking with crap or water in the carbs.

[SDN]

No carbs are OK coz it starts like a dream on remote tank and runs fine, there is a vacuum powered diaphragm fuel pump

[Rich]

there is a vacuum powered diaphragm fuel pump

Must work on impulses then I though it was just a cut off valve - good job I'm going to use EFI Have you taken it to bits and checked the diaphrams are clean and seating correctly. Did you connect the remote feed through that or direct to carbs?

[Con Rod]

the fact that it starts ok and then diest suggests there is a blockage, kinked hose prehaps? same goes for the vacuum hoses. Mat sure they are not kinked or damaged and are connected to the spigots on the inlets

You can test the fuel tap pretty easily if you dont mind spilling a bit of petrol, same goes for the vacuum pump.

Not unusual for a bit of water at the bottom of the tank to get sucked into the carbs when you go to reserve so no harm draining the float bowls

[SDN]

Right checked fuel tap its good filters clear and it feeds fuel on prime, put some suction and reserve and main work.


Carbs been off no blockages no crap in float bowls

Brand new fuel pump

Bike starts and runs on a gravity remote tank

Connect fuel tank and it is really difficult to start and when running, is not filling the fuel filter chamber its like pump is not delivering - might try new vacuum pipes.

[SDN]

Tested vacuum pipes last night and both sound, swapped pump over to other inlet manifold same result.

Seems like non return valves on new pump are not working, allowing fuel to run back, possible reason for fuel filter chamber not filling and fuel seems to be moving backand forward when pump is operating - Possibly on remote tank, there is more static head as it is higher than the fuel tank.

Any ideas?

[Excalibre]

Sounds like a blockage somewhere between the fuel tap and the carbs. Try a new inline filter, the current (almost new) one may have become blocked from crud when you ran the tank dry.
Is the filter installed the right way around? It'll have an arrow on it to indicate direction of flow.
Check carefully for hoses that are kinked, getting pinched when the tank is lowered or have tight bends. Did you shorten the hoses a bit to allow for the length of the filter when you fitted it?
Check the tiny filter screen that fits in the T-piece at the carbs. Is it blocked, has it become dislodged and jammed itself in the fuel hose? As you're using an inline filter, I suggest getting rid of it altogether anyway.
Is one of the vacuum hoses connected to the pump?
Have you connected the fuel hoses the wrong way around at the pump?

Good luck

[SDN]

Thanks for coming back - checked all that, not a problem, now decided to check the fuel pump non returns by blowing down the outlet to the pump and I could blow straight through, so I reckon my brand new pump non return is passing and fuel is just moving back and forth - does my logic check out? Don't want to look like a holiest of holy sending a good part back

[Rich]

sounds like the logic is right, if the old one worked before running out I would take it to bits and check it for crap assuming it is connected up right.
Have you read this:
http://www.trx850.com/phpBB_forum/viewt ... =37&t=9741

[Excalibre]

Thanks for coming back - checked all that, not a problem, now decided to check the fuel pump non returns by blowing down the outlet to the pump and I could blow straight through, so I reckon my brand new pump non return is passing and fuel is just moving back and forth - does my logic check out? Don't want to look like a holiest of holy sending a good part back

I agree, if all that checks out, to quote Sherlock Holmes, "......when you have eliminated the impossible, whatever remains, however improbable, must be the truth".

It must be the pump!

[cobbadiggabuddyblooo]

Have you tried disconnecting the fuel pump from the tap, crank the motor over and see if the vaccum line attached to the tap does as its suppose to. The vaccum line should open the tap to allow fuel to flow from the tank to the pump.

Then try attaching a fuel line from your gravity remote tank to the pump and make sure the vaccum line is attached and disconnect the fuel line to the carbies.
crank the motor and see if your pumping fuel.

This way you can see that both vaccum operated devices are doing their jobs.
Attach everything back as std but keep the fuel line disconnected from the carbies and crank away to see if you have a fuel feed to the carbies.
Also check the vaccum feed spigots are not blocked at the manifold.

[SDN]

Have you tried disconnecting the fuel pump from the tap, crank the motor over and see if the vaccum line attached to the tap does as its suppose to. The vaccum line should open the tap to allow fuel to flow from the tank to the pump. I know the tap works, coz if I suck the vacuum pipe fuel flows - also fuel runs out fine on prime, I also stripped the tap checked the filters and all the diaphragms - all good. I checked both vacuum pipes and they were fine, also checked that I was getting Vacuum from both pipes as I was cranking motor
Then try attaching a fuel line from your gravity remote tank to the pump and make sure the vaccum line is attached and disconnect the fuel line to the carbies.
crank the motor and see if your pumping fuel. Done this and fuel was pumping, but fairly weakly, I think my new fuel pump has a poor NRV seat which is aloowing fuel to flow under no back pressure, but add in gravity and fuel filter resitance and the NRV not seating is allowing fuel to flow back This way you can see that both vaccum operated devices are doing their jobs.
Attach everything back as std but keep the fuel line disconnected from the carbies and crank away to see if you have a fuel feed to the carbies. Fuel feed is present, but very weak and running back and forwards - fuel will not fill the transparent filter housing, there is just a small amount of fuel at the bottom of the filter housingAlso check the vaccum feed spigots are not blocked at the manifold.

I would say they are not blocked as I am getting vacuum

[cobbadiggabuddyblooo]

You tried the tap by your mouth but not the motor did you say???
You mentioned earlier you swapped the vaccum lines around and tried the fuel tap vaccum line on the pump. If the spigot is blocked that feeds the tap when the vaccum lines where swapped you may still have the same problem but may have missed this by checking the tap with your mouth.
Sounds padantic but this way your actually testing the fuel tap vaccum under real conditions.
I would suggest checking the fuel tap again via the vaccum line attached to the motor.
Blow back down each vaccum line just to double check there is no blockage at the spigots.

Very unusual for a new vaccum pump from yamaha would be faulty off the shelf but hey, nobody is perfect.

[SDN]

Cheers Cobba will double check the vacuum lines - but I have felt vacuum on both pipes with the bike running - but maybe there is reduced vacuum. I would rule out the tap because the problem persists on prime and I pulled off the pipe while the tank on prime and tank was on the bike and got drenched in fuel! So I know fuel is getting from the tank when on prime and the problem with the fuel persists when tank is on prime

The pump I am afraid is not a genuine Yamaha item, but pattern so possibly not built to the same quality and the fact that I can blow fuel from the pump outlet to the pump inlet points to a problem with the NRVs. I should be able to blow from the inlet to the outlet but not from the outlet to the inlet.

On vacuum stroke drawing fuel in, outlet NRV is closed inlet NRV open on pressure stroke inlet NRV closes outlet NRV opens

If outlet NRV is not seating, on the vacuum stroke the pump will be pulling fuel back down the line from the carbs

If inlet NRV is not seating, on the pressure stoke, fuel could be pushed back towards the tank as well as up to the carbs

As I can blow from outlet right back to inlet would suggest that both valves are not seating

I think my logic is good but dont want to waste any more riding time chasing down a blind alley - so any critique is welcome