wallaby Posted March 16, 2013 Share Posted March 16, 2013 Let's start fresh with this jetting project: I have a Holley 770 street avenger carb. It was chosen by my engine builder, and installed and dynoed just as it came out of the box from Holley. The dyno numbers are good, but my wide-band air/fuel ratio meter indicates it runs rich all the time. Right now it shows it at 13.2 or 13.4 at cruise and WOT. The idle mixture is close to that as well. I've noticed that engine temp will change the ratio numbers: as the engine temp goes up, the richer the mixture reads. I'd be willing to bet that ignition timing changes will alter the ratio reading also. My thinking is that since this is a vacuum-secondary carb, I can lean out the primary jets a bit to give me a number in the low 14:1 range at cruise, and fatten up the secondary jets to get a ratio in the upper 12's for WOT. Does this sound practical? At what point do I consider tinkering with the power valve setting? Not sure what that gizmo does. I have also seen metering blocks that have a needle valve for jet adjustment so you don't have to tear down the carb multiple times getting it dialed in, but It seems like it would be nearly impossible getting equal settings from side to side without multiple air-fuel-sensors. It looks as if I need to order up a bunch of jets to find what works. Let me know if I'm going about this wrong. Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted March 16, 2013 Share Posted March 16, 2013 that's how I would star Mark what's your vacuum at idle? you should know this before changing the power valve Quote Link to comment Share on other sites More sharing options...
wallaby Posted April 7, 2013 Author Share Posted April 7, 2013 Ok, this was different from what I'm used to. With a Q-jet you can change jets or rods without removing the carb and no spilled fuel. The Holley is a bit different. I should have just removed the carb and done everything on the bench from the get-go. With that minor gripe out of the way, the re-jet project went well today. The carb had #72 primary jets and was too rich at cruise (13.4), so I went down two steps to a #70, hoping to see a 14-something mixture at cruise. The carb ran lean at WOT to begin with (13.4) and with the new leaner jets in the primaries, I figured 4 steps up would be a good starting point for the secondary jetting. The seconary side had #75 in them, so I went up to a #79. Everything checked ok at idle afterwards, and I was able to get a leaner idle mixture and get rid of the smelly fumes I had before. Time for the test drive. OMG this made a difference: not only did I get a cruise mixture in the low to mid 14's, and a WOT mixture in the mid to upper 12's, but this thing came alive and I can feel a difference in the seat of my pants! The WOT condition has really improved. It must have been hungry for fuel; I broke the tires loose on a 2-3 shift and don't remember that happening before! It's almost as if the secondaries hadn't been opening before....but now I hear a distinctive growl from under the hood, and the engine pulls like a freight train. There's no doubt they're opening now. I still need to spend some time driving it to see if it likes where I've set it, but so far there has been a great improvement in just a couple of jet sizes. Thanks everyone for helping with this. Quote Link to comment Share on other sites More sharing options...
amsterdam84 Posted April 8, 2013 Share Posted April 8, 2013 Lol Mark I didn't recognize you with the new avatar at first. Quote Link to comment Share on other sites More sharing options...
72 LS5 Posted April 8, 2013 Share Posted April 8, 2013 I have got to get a wide-band. That's the only way to really get it dialed in! Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.