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Fuel starvation


bobzilla7
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When tackling a a couple of recent steep climbs, I seem to be not getting enough fuel to the carbs (brand new SUs). The tank is in the rear of my Tomcat and so is the electric Facet fuel pump. Would I be better putting it near the carbs to pull the fuel up, rather than pushing it?

Or any other thoughts?

Thanks

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isnt a bigger wallet the normal cure for fuel starvation on V8s? :ph34r:

random thought - are the fuel pipes big enough to flow the amount of fuel you need? and not kinked anywhere & so forth.

I'm pretty sure there are no kinks, but it's worth a check.

It only seems to be when the vehicle is facing up on a steep slope, so if the pipes weren't big enough, I'd be getting fuel starvation at other times as well I'd have thought. I'll check the wallet as well! :D

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SU's are easy to take apart though its been a while since I saw one. I can recall the float bowl on the side, how is the float retained (hinged IIRC but don't know the orientation)? It could be on steep ascents the float is not able to rise enough and you're getting a lower than normal fuel level in the float (and hence at the main jet) which will lead to fuel starvation.

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SU's are easy to take apart though its been a while since I saw one. I can recall the float bowl on the side, how is the float retained (hinged IIRC but don't know the orientation)? It could be on steep ascents the float is not able to rise enough and you're getting a lower than normal fuel level in the float (and hence at the main jet) which will lead to fuel starvation.

Yes, that seems a possibility, although my last V8 on SUs didn't seem to have a problem. Someone else suggested fuel vapourisation so I might try heat wrap over the fuel lines in the engine bay.

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Have you installed a flow and return system or just dead ended the flow at the carbs?

A flow and return system stands a better chance of keeping constant fuel availabilty at the carbs as vapour is flushed back to the tank. The fuel pressure at the carbs depends upon the pump pressure and the size of the restrictor you fit in the return.

jw

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My old pick-up used to run very hot all the time, but never ever suffered vaporisation even after a long run.

The float bowl was on the side of the old ones, HIF's which is the ones you want have the float bowls beneath the piston.

Does this mean I can't do anything about it?

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A swirl pot, as the name suggests, lets fuel swirl round inside. A bit like a Dyson vacuum cleaner, the heavy fuel goes to the outside and then the bottom and the lighter air/vapour comes off the top and is returned to the tank. Worked wonders on the 109 between lift pump and EFi pump, stopped the vaporisation problem dead. I'm not so sure that a swirl pot would be the ideal answer for you, for starters they usually need a feed in from a pump and then another pump to take the fuel out, since the pot is effectively open at the top it won't hold fuel pressure, although I restricted the return pipe on mine a bit (using a small inline fuel filter) to help force-feed the EFi pump.

Another method is to mount a small "pot" in the bottom of the fuel tank (not so easy on an already-made tank) and pickup the fuel from that, so that even if the majority sloshes away from the pickup it's still sat in a small pool of fuel.

Jet-ski fuel pickups are another option, they are a heavy end on a flexi pipe, so as the vehicle pitches the end follows the fuel.

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A swirl pot, as the name suggests, lets fuel swirl round inside. A bit like a Dyson vacuum cleaner, the heavy fuel goes to the outside and then the bottom and the lighter air/vapour comes off the top and is returned to the tank. Worked wonders on the 109 between lift pump and EFi pump, stopped the vaporisation problem dead. I'm not so sure that a swirl pot would be the ideal answer for you, for starters they usually need a feed in from a pump and then another pump to take the fuel out, since the pot is effectively open at the top it won't hold fuel pressure, although I restricted the return pipe on mine a bit (using a small inline fuel filter) to help force-feed the EFi pump.

Another method is to mount a small "pot" in the bottom of the fuel tank (not so easy on an already-made tank) and pickup the fuel from that, so that even if the majority sloshes away from the pickup it's still sat in a small pool of fuel.

Jet-ski fuel pickups are another option, they are a heavy end on a flexi pipe, so as the vehicle pitches the end follows the fuel.

Hmmm, an interesting idea, especially the flexi pipe which I could possibly adapt from the existing pick-up.

Has anyone esle tried this before?

I might try restricting the return to tanks as well as perhaps the fuel just wants to return via the easiest route!

How small a pipe did you down size it to?

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i never knew jetskis had that sort of pickup. thats known as a clunk tank in the RC aircraft world, cause you turn it over & the pickup goes cluck down to the 'new' bottom of the tank.

possibly just extend/bend the pickup in the tank towards the rear, ive never seen inside a series tank though so that might not be practical.

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i never knew jetskis had that sort of pickup. thats known as a clunk tank in the RC aircraft world, cause you turn it over & the pickup goes cluck down to the 'new' bottom of the tank.

possibly just extend/bend the pickup in the tank towards the rear, ive never seen inside a series tank though so that might not be practical.

The things you learn on here, eh?!!!

It's a straight pipe going more or less from the top to bottom with a filter on the end. It should be fairly easy to cut the pipe and fit some flexi-hose in the middle as long as i can find something that's happy sat in petrol (standard petrol pipe?).

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I might try restricting the return to tanks as well as perhaps the fuel just wants to return via the easiest route!

How small a pipe did you down size it to?

Well I just stuck a small bike filter inline:

ff100.jpg

But a mate used a biro cap down the fuel hose instead, fuel is very searching and will flow through a small hole surprisingly easily.

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Jet-ski fuel pickups are another option, they are a heavy end on a flexi pipe, so as the vehicle pitches the end follows the fuel.

Fridge Freezer / Andy, this could be it. I've just realised that the pick up on the tank is off set to the side (in my case the front) - normally this wouldn't matter as the tank would be the other way around and consequently in the middle, so it could be quite possible the the fuel is not getting to the pick-up once it gets down to a certain level.

I could either spin the tank around so the pick-up is at the back giving me the advatage when I need more fuel going up a steep gradient (not quite so important on the way down, well usually anyway) or I could fit a flexible feed. Which leads back to my last question - will a fuel hose be happy sat in petrol? If not, what could I use?

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  • 4 weeks later...

Just a thought but have you had a look at the pick up pipe inside the tank?

It would originally have had a copper mesh around the open end which could be partially blocking the intake. The pick up pipe is also very soft so might have been bent forwards. I suppose you could try pointing it backwards since fuel starvation going downhill is less of a problem.

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