Throttle Position?

Road-race engines and ancillaries - general discussion
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beardybloke
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Location: Bristol , England
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Throttle Position?

Post by beardybloke » Tue Feb 03, 2015 7:31 pm

I have a 1600 Fiat twin cam in a 1975 TVR , I have stuck with the 32ADF carb , I know the advice would be to replace but having spent quite a bit of time on it I think i can get it to work so I am happy with it . What I would like to know is at what point in the rev range should the secondary open , at the moment this is opening too late but I can fix this by shimming the cam so it opens earlier . I am assuming that it should be around 3000rpm but would like some advice . Once I have it adjusted correctly then I will have a better view of whether I want to keep it or not . Any advice would be welcome.
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FiatRally
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Re: Throttle Position?

Post by FiatRally » Wed Feb 04, 2015 7:11 am

Hallo Beardybloke,

To my understanding all Weber ADF carbs are mechanical progression.

If this is so then it is not the revs that determine when the second choke opens but your foot on the pedal.

If you cruse with your foot light on the pedal the second choke should stay closed but then when you put it down the second should open.

Fuel economy is what makes the ADF so good.

I used to set up the 34ADF that at full throttle the second choke butterfly is just fully open and that worked well for me.

It was light on fuel if driven just on the first choke, but would really get a kick when the second choke was pushed open at around 3400 rpm.

Hope this helps.

I will look for my weber book.

Ciao,

Ernst
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beardybloke
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Location: Bristol , England
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Re: Throttle Position?

Post by beardybloke » Wed Feb 04, 2015 7:32 pm

Hi Ernst , thanks for that . It is correct that the ADF carb has a mechanical secondary , I maybe looking at this incorrectly but I am assuming that as you put your foot down the primary opens and as it does it comes into contact with the secondary cam lever and so progressively opens the secondary .
This maybe wrong but it seemed that the secondary is not opening early enough so I am loosing power at the high rev range , my solution was going to be to pack the top of the secondary cam so it gets hit earlier by the primary , certainly will open earlier then !. Fuel economy is very good around 32mpg however hard you push , so again this makes me think that it is not opening early enough , but maybe I need to put my foot down more aggressively ?.
I am thinking from your experience that the secondary should open around 3,400rpm ?. If so I will try to reproduce that .
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