Houseoffubar
Well-Known Member
661 on both jets!
What the hell is this?
Thanks for any input!
OOOOOH! now I get it. Holley is only perfect when its Federal regulated emissions.Because of the tolerances of the holes. So in the standard sizes, a #66 = approximately 0.066" diameter. Maybe the hole is .0658"-.0662" or something? But they never checked the actual flow. The "close tolerance" jets like your #661 is supposed to flow exactly what a #66 or 0.0660" diameter jet is supposed to flow. They were used to meet emissions regulations.
That designates high flow.I have some with an H after the number ?
I’m not sure the age, it is a 9834-1That designates high flow.
The jet would flow a hair more than rated but not quite up to the next size.
I don't know about the 3rd digit, but I'd just assume take the other guys word for it to no real consequence.
They've intro'd and discontinued many things over the years, like the anti siphon/anti pull over nozzels.. went from ball to valve pin under the nozzles at the same time...then no brass tubes...then brass tubes...economizer pv's.
How old is this carburetor?
That explains it even better.Holley Jet numbers are all flow based. You can find two jet sizes with the same diameter bore because the lengths of the bore and the entrance and exit shapes are different.
A two digit standard jet is allowed 3% variation in flow.
Three digits ending in 1 or 3 were used by factory calibration, and I too have found H on a jets installed by the factory.
Three digits were also used for close-limit jets with only 1.5% flow difference allowed.
Last are three digit metric jets used on model 4360 and 5200 carbs.
(ref. Mike Urich & Bill Fisher Holley Carburetors and Manifolds HP Books. Holley part No 36-73, 1987 revised)