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Jac Mac · 02-12-08, 06:20 AM

Where is the problem, the pump shooter has a known size which you tailor to the requirements of the application during the acceleration phase. One would assume that the PV would also be in operation at WOT so for jetting purposes the PV, Main jet,& pumpshooter orifice areas are all added together to get the total actual main circuit size, but the main jet is the only size that can be changed without interfering in other parts of the operating envelope--acceleration--part throttle operation etc. Quite a handy feature to have when you think about it, at lower to mid range rpm when the airflow rate is not as high you have the main jet plus perhaps some PV then when your at WOT & high RPM the shooter adds a bit more. The closer the nozzles of the shooter are to the venturi, the more sensitive they will be to pullover.

On some alcohol carbs etc the metering block will have a known size drilling alongside the main jet so that normal holley jets can be used as once you start using large size single hole jets accuracy in jet flow rates is difficult to maintain.
For example the Holley #80-81-82 jets all share a bore size of 0.093", the flow rates being increased on each size by the bevel or lead into & out of the jets.
The #69-70-71-72 jets by comparison increase by0.003" for each size-0.070", 0.073",0.076",&0.079".

02-12-08, 06:20 AM	#2 (permalink)
Jac Mac jac mac 10 tenths Join Date: Dec 2005 Location: Gore N.Z. Posts: 1,562 Rep Power: 20	Re: 4-barrel Pullover... Where is the problem, the pump shooter has a known size which you tailor to the requirements of the application during the acceleration phase. One would assume that the PV would also be in operation at WOT so for jetting purposes the PV, Main jet,& pumpshooter orifice areas are all added together to get the total actual main circuit size, but the main jet is the only size that can be changed without interfering in other parts of the operating envelope--acceleration--part throttle operation etc. Quite a handy feature to have when you think about it, at lower to mid range rpm when the airflow rate is not as high you have the main jet plus perhaps some PV then when your at WOT & high RPM the shooter adds a bit more. The closer the nozzles of the shooter are to the venturi, the more sensitive they will be to pullover. On some alcohol carbs etc the metering block will have a known size drilling alongside the main jet so that normal holley jets can be used as once you start using large size single hole jets accuracy in jet flow rates is difficult to maintain. For example the Holley #80-81-82 jets all share a bore size of 0.093", the flow rates being increased on each size by the bevel or lead into & out of the jets. The #69-70-71-72 jets by comparison increase by0.003" for each size-0.070", 0.073",0.076",&0.079".