Hemi AFB jetting

Discussion of the 426 Street / Strip HEMIs.

Moderators: TrWaters, 392heminut, scottm

Post Reply
Posts: 1
Joined: Sun Jan 31, 2010 12:43 pm

Hemi AFB jetting

Post by 68jim » Sun Jan 31, 2010 4:10 pm

Hello TheHemi.com,

I found your site during a google search for this topic. I belong to a few other forums and I'm usually amazed at the level of knowledge and experience out there on the internet. I have a question about Hemi AFB jetting. I have a 68 Road Runner with a Hemi rebuilt back to stock (factory solid lifter cam, exhaust manifolds, dual point ignition, etc.). The stock carbs were rebuilt but the existing rods and jets (at that time) were left in place. The car runs pretty good and I’m not blowing black smoke out the exhaust. But stand behind the car at idle after it being fully warmed up and it smells very strong from being too rich. The previous owner mentioned that he thought the carbs were set up per the old Direct Connection Book instructions for Super Stock, however I checked it against those numbers and they do not match. I mapped the area of the jets vs. area of the metering rods of what I have against the factory jetting and found that I’m running 40%-60% richer on the primaries and that the secondaries are either same as stock or in one case 30% leaner. I have noticed in the Mopar forums that many Hemi owners state that the factory jetting, with today’s gasoline blends, tends to make the motor run on the lean side. Most have said that they either fattened the jetting or reduced the metering rod diameters but did not call out actual numbers for both rods and jets. Anyway, these are the jets/rods currently in my carbs.

Front carb – Pri .101, Sec .080 / Rod #341 (.068/.059)
Rear carb – Pri .098, Sec 077 / Rod#544 (.0715/.058)

Factory jetting is this,
Front carb – Pri .089, Sec .080 / Rod#341 (.068/.059)
Rear carb – Pri.089, Sec L.092 R.077 / Rod L #543(.069/.054) Rod R#544 (.0715/.058)

I would like to hear from others who have gone this route before with a stock Hemi. What combo of jets/rods did you end up with? I noticed that the factory jetting for the rear carb went richer on the left side vice the right side. I’m assuming that they were compensating for fuel distribution issues with the stock intake manifold??? I’m guessing that jetting would need to be 10%-20% richer for today’s gasoline blends???

Post Reply