Fuel starvation - likely causes, things to check etc?

[Taipan]

Hi All

I'm trying to track down the cause of the problems i'm having with my bike (see airbox mod thread). I'm becoming suspicious that it may be a fuel delivery problem and not a ram air issue. I'm not familiar with these bikes at all, so if I've missed anything out or if you know of a good way to check anything please let me know.

1. I've checked all the fuel pipes and there are no kinks in the pipes.
2. The fuel appears to flow freely from the tap from both the on and reserve settings.
3. Fuel pump - if this wasn't working would the bike still have some gravity feed? Can you feel the pump clicking? If I put the outlet into a bowl should it deliver x amount of fuel in x amount of time or suchlike?
4. Fuel pump relay - how can I check this? Or can it be bypassed to eliminate it from being the cause?
5. Is there a tank breather or does it just vent through the cap?
6. Have I missed anything?

Many thanks.

[Steve-TC1]

Fuel filter dirty or blocked or fitted wrong way round

no feed if pump isn't working

Try put the exit pipe from the pump to the carb in a milk bottle and hit the starter button , you'll know if there a good supply

[yorkie]

Yes the fuel pump relays are prone to going tits up, and can cause other problems with the number 1 coil and ic ignitor unit.
The book say how to check it with a multimeter.
You can conect the pump straight to the battery and it will pump like mad, same happens when you press the starter button, but once released its the spark pulse to number 1 coil that pumps it when that fires.
You can feel the pump pumping by resting your finger on the black cap of the pump where the wires go in.

[Steve-TC1]

[Taipan]

Top information! Many thanks Chaps. Hopefully i can get on and check all that out and "eliminate them from my enquiries"! It does sound like it could be the fuel pump relay based on that description?

[abacky]

You should also check the wiring going to the relay, i had this problem and it would start but the pump would only fill the carbs once and the fuel would only last approx 5-10 mins then it would cut out this was down to a brocken wire going to the relay.
Another problem with fuel delivery i had was the pump its self, under the black end cap there is a points type system for driving the pump and i had to clean the points with a nail file otherwise it would onlt work intermitantly and then the points welded togeather once i cleaned them its been fine ever since.
You can feel the pump working when you press the starter and every few seconds when its running.

[Taipan]

How obvious is it when the pump is working? I can't feel mine clicking when I press the starter or when its running or if I can its very faint?

[irish-zx9r]

i had the same problem it was caused by a kinked fuel pipe going from the tank to the fuel filter.
when i lifted the tank and the fuel line was not kinked the bike was perfect so
i replaced it with a new fuel pipe and never had any trouble with it since.

[Steve-TC1]

[hey9r]

Nice car mats

[abacky]

Not only is the pump operation easy to feel if its working you will know by touch and you can hear it this sounds the same as the problem i had when the when the points welded togeather, then the pump wont work and you will feel nothing.
If you have the tank off its easy to get the pump off and remove the black end cap only 1 screw holds it on and you can operate the starter and see the pump working be carefull of petrol fumes as the point will spark if its working.

[Steve-TC1]

Nice car mats

Not mine m8 , yet another pic nicked of ebay

[Taipan]

Hi All

Ok I got the filter through and whilst they look identical the inlet from the tank end is a slightly smaller bore and the squeeze clip wouldn't nip it up enough to make it leak free. A jubilee clip nipped it up ok though. So it can be fitted if you want it to. The bore size is of a minimal difference and as the carbs are demand fed and not constant I think it safe to say the bore size wont cause any problems.

My filter was dirty, not blocked but certainly clogged. But the good news is it looks like that was the cause of my problems! It couldn't maintain enough fuel flow at motorway speeds over a few miles and hence the problems i was having. I was pretty convinced that it couldn't be a ram air issue, although that may have been contributry at speeds, but if it was just that it should have equalised pretty much straightaway when I slowed down, which it didn't.

So I now have a near perfect running bike, or at least one I can now get set up on a dyno. I'm one happy man! Many thanks to all for the advice and help given.

[Taipan]

Short victory, it reverted to type on the way home tonight. Ahh the familiar surroundings of being back at square 1.

[Steve-TC1]

Could it not be carb ice