HIF6 Carbs Flooding

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jimthesail
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HIF6 Carbs Flooding

Post by jimthesail »

Ahoy !
Encountered flooding probs. with pair of HIF6s in old SD1 V8 in a neglected kit car.
Assumed it was needle valves so replaced and adjusted to 2mm above the base of float chamber rather than 1mm below to give wiggle room. (had a bit of experience with another kit car) No flooding. Having solved other ignition problems but still not starting, have returned setting to 1mm below. Flooding returned !
Being that sort of bloke I have calculated the pressure available to locate needle valve against seat. ( Specific gravity of fuel, volume of float, length of float arm, diameter of needle valve, blah, blah ! ) My conclusion is that the available force is only equal to 5psi. So ! Fitted a Malpassi regulator which is screwed right down ? My final conclusion is that the whole system is suspect and bearing in mind that the float 'bottoms' (actually tops) before the spring in the needle valve fully compresses, that the volume of fuel is small compared to the float volume and that the angle of the carbs must work against any accuracy I am, to put it mildly, not impressed ! Anyone care to add anything before I set light to it ?


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stevieturbo
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Re: HIF6 Carbs Flooding

Post by stevieturbo »

So have you actually measured fuel pressure ?

Certainly on HIF44's....they really don't like much over 3-4psi.

Have you tried holding the valve shut and blowing or applying light pressure to the inlet to see if it is even capable of sealing ?
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jimthesail
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Re: HIF6 Carbs Flooding

Post by jimthesail »

"so replaced and adjusted to 2mm above the base of float chamber rather than 1mm below to give wiggle room. (had a bit of experience with another kit car) No flooding. Having solved other ignition problems but still not starting, have returned setting to 1mm below. Flooding returned !"

I replaced with new needle valves which sealed at 2mm above but fail at 1mm below so suspect something other than pressure against needle valve is amiss ?
JimtheSail

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ChrisJC
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Re: HIF6 Carbs Flooding

Post by ChrisJC »

Have you measured fuel delivery pressure?

Chris.
--
Series IIA 4.6 V8
R/R P38 4.6 V8
R/R L405 4.4 SDV8

jimthesail
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Re: HIF6 Carbs Flooding

Post by jimthesail »

Thanks Chris ! Long story short. Bought Ebay pressure gauge (0 - 15psi) and tested pressure
with engine off as tried before and no Malpassi regulator. 4psi on the nose. Reconnected
and started engine, no flooding. Such joy ! I am of the opinion that the needle valves are
marginal in their ability to shut off fuel and if you move/rotate old ones they will start to leak
and new ones need the vibration of the engine to seat properly ? Thanks for help, gauge was
cheap as chips !
JimtheSail

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ChrisJC
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Re: HIF6 Carbs Flooding

Post by ChrisJC »

Good news!

I've always thought they were a bit marginal, prone to excess pressure or dirt or wear.

Chris.
--
Series IIA 4.6 V8
R/R P38 4.6 V8
R/R L405 4.4 SDV8

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