416 carby question

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Arbian
Posts: 97
Joined: Wed Oct 23, 2013 9:02 pm
Location: Perth

416 carby question

Post by Arbian »

Do the holes on a 416 needle jet need to be lined up in a specific orientation on replacement post cleaning ...... and second dummy question ... is a needle jet and pilot jet the same thing ... if not where is the pilot jet on these carbs?
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never-outbored
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Re: 416 carby question

Post by never-outbored »

Needle and pilot jets are not the same, pilot jet controls the idle circuit, needle jet controls everything after that up until about 3/4 throttle and then 3/4 to WOT is done by the main jet, as far as i'm aware
Arbian
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Location: Perth

Re: 416 carby question

Post by Arbian »

So I am guessing the pilot jet on the 416 is the cast very narrow tube (no removable brass piece) to the side of the main / needle jet tube? I cut a knackered carb in half to try and see where the jet / air passages were but the pilot jet tube seemed to be blind ending .... I am guessing it turns sideways into the side of the needle jet tube but that the thickness of my hacksaw cut removed it. Don't suppose anyone has a schematic so I can get my head round it??? I am guessing the passages on the 418 from the Curlew follow the same routes (but the pilot jet on this seems to have a pressed in brass tube.
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Charles uk
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Re: 416 carby question

Post by Charles uk »

Try removing the jet from a 400 series carb.

You will see in the bottom end of the hexagonal jet a hole in the side to permit fuel entry & in the centre a small hole (circa 1mm dependant on the jet size stamped on one of the flats) this allows a metered amount of fuel into the emulsion tube above the jet.
You will notice from the the bottom of the throttle slide a tapered needle projects into the top of the emulsion tube, at no point during opening the throttle does this needle come out completely, as you open the throttle the needle rises reducing the needle diameter increasing the hole area & permitting greater fuel flow, giving a fully metered fuel flow throughout the throttle opening/rev range.

This means you don't need a pilot jet for low revs plus a main jet, one controlled jet does it better, often with better fuel consumption!
Make it idiot proof and someone will make a better idiot.
Arbian
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Joined: Wed Oct 23, 2013 9:02 pm
Location: Perth

Re: 416 carby question

Post by Arbian »

Thanks Charles, But what does the little passage in the casting at the side of the main jet do? On the 416 it is plain and on the 418 it has a brass insert.
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Charles uk
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Re: 416 carby question

Post by Charles uk »

Is that the air inlet re-stricter for the emulsion tube?
Make it idiot proof and someone will make a better idiot.
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