changing q-jet secondary rods

[Dissident]

Originally Posted by Alan Nyhus

Dave, the tendency of QJets is to run rich as air flow increases (rpms going up). Secondary metering rod changes alone don't always fully address this. Also, the primary side can contribute close to 40% of the total fuel flow at W.O.T.

Hope this helps. -Al

Mr Nyhus and Others that might be interested in some facts from measurements,
1) Most 750 type QJs flow test to be from a very poor low of 164cfm to an average of 170-175cfm at 20.4"H2O test pressure.
2) Most 750 type QJs flow test at 660cfm to 675cfm on the secondaries at the same test pressure as above.
3) Doing some quick math to see how much that is in mass flow of air in lbs/hr at sea level, yields 798 lbs/hr on Primaries and 2622 lbs/hr on Secondaries.
4) Allowing for max power at somewhere near 12.5:1 A/F ratio would yield fuel use on primaries of 63.84lbs/hr (127.68Hp) and 209.76lbs fuel use on secondaries (419.52Hp) supplying a total of 547.2Hp

As you can see, that is 23.33% fuel on primary and 76.67% on the secondary. IF one sees that the primary is supplying the 40% as claimed in the quote, one can only assume the secondaries are not at WOT or something is categorically wrong with the carburetor or the fuel supply system tune.

Hope that helps.....No, I do not have a race car but have supplied assistance to make more than a few more than competitive.

Regards,
HB2
Dissident