Author Topic: carb jet confusion  (Read 515 times)

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royblackburn1@btinternet.

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carb jet confusion
« on: 09 March, 2017, 12:01:07 »
 hi I have a imported 1966 lightning can anyone tell me the correct size jets and needle position for the concentric carbs numbers  932 R300 and 932 L301 I have been told the engine is running rich and why are there so many variations on the same engines through out the years. thanks Roy

JulianS

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Re: carb jet confusion
« Reply #1 on: 09 March, 2017, 12:22:22 »
Your 1966 Lightning would originally have been fitted with a pair of 1 5/32 inch monoblocs.

The later Lightnings were fitted with a pair of 30 mm concentrics.

Your 300 and 301 carbs are "generic" 32 mm concentrics recent pattern. I presume they are standard ones rather than the premier version with the upgraded idling system

I think you will have to experiment to get the carb settings  correct because of the non standard size carbs, but suggest that you start with the jetting for the A65 Spitfire MK3 which also had 32 mm concentrics.

Spitfire specs were 190 mains, 107 needle jets and needle in position 2. The pilot jet in your carb would have been a pressed in pilot bush.

There is a lot of information available on the Amal website. Worth viewing.

This link takes you to the standard spec for 932/300 supplied by Amal.

http://amalcarb.co.uk/mk-i-concentric-series/900-series/base-line-specifications/32mm-bore/rh-32mm-4-stroke-mk-i-carburettor.html

Bess

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Re: carb jet confusion
« Reply #2 on: 09 March, 2017, 12:45:22 »
Hi,
    I have this document that I've been using.

royblackburn1@btinternet.

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Re: carb jet confusion
« Reply #3 on: 10 March, 2017, 11:47:22 »
Thanks guys for the information will go down the spitfire route, but why all the variations? Roy

JulianS

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Re: carb jet confusion
« Reply #4 on: 10 March, 2017, 12:28:45 »
There were some changes to the concentric during the 60's as it developed - float bowl with drain plug introduced, the needle jet holder and the needle dimensions changed (as a matched pair) and the detachable pilot jet was replaced by a pressed in pilot bush which may have contributed to the variation but I suspect that practical experience may also have contributed.