Carburettor tuning

PostPost by: BobC » Mon Feb 01, 2021 9:30 pm

Does anybody out there know of somebody who can set up carburettors? My big valve has twin Dellortos that I have set to manufacturers settings, right in and two turns out etc. The engine runs well but I just feel that the touch of a maestro would set it up perfectly. I live in the north west of England on Merseyside, so would appreciate if there was somebody in this neck of the woods. Thanks in anticipation. Bob
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PostPost by: elans3 » Tue Feb 02, 2021 8:01 pm

Bob, don't rely on "doing it to the instructions" too much. There are too many variables, particularly in an engine, or carbs that aren't freshly rebuilt. If you haven't got a snail type Synchrometer, then beg steal or borrow one, they're worth their weight in gold.
You're obviously au fait with tuning carbs to a degree, so let the engine run until it's fully warmed up (preferably on a run on the road), ie until the thermostat has opened.
Balance the two pairs of carbs with the synchrometer first, also checking that each barrel of each carb is flowing the same amount of air. Hopefully they will be, but if not, then you've got a twisted throttle spindle - another story for another day.
Then set about the idle screw, setting the idle revs to 1000rpm.
Then screw each idle air/mixture screw in or out, until the engine revs rise to a peak, don't go further than that.
Do that for all four , each time re-setting the idle speed to 1000 rpm before adjusting.
Then repeat, until you're sure that you've reached peak idle speed on each screw.
Job done.
It doesn't matter how many turns out they are, unless you get to more than say, three turns out, then if you're not getting good running & progression, without spitting back through the carbs, you need a richer idle jet.

They won't all be exactly the same number of turns out, trust me, but they should all be within 1/4 of a turn- ish.
There are lots of variables, ie valve clearances, plug gaps, HT lead condition, just to speak of a few, and if those aren't absolutely spot on perfect, then each cylinder will burn slightly differently.
In both my Alfa Twincam, and my Elan, mine are all different, but when I pull the plugs after a good run, the colours are all good & match, and they both run like a sewing machine.
Last edited by elans3 on Tue Feb 02, 2021 10:06 pm, edited 1 time in total.
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PostPost by: BobC » Tue Feb 02, 2021 8:25 pm

Thanks for fulsome and helpful reply, I have got an airflow meter so will go through the procedure that you outline. Again many thanks for passing on your experience. Bob
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