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I've been out of town for the past week, and wasn't able to work on my C3. When I got home, my new AEM gauge was waiting for me from the AEM warranty department. They sent me a full new kit, so now I have a spare wideband, which is a big plus! I popped the new gauge in and it immediately started working once I fired my car up. I took a quick spin just to get a baseline on my Edelbrock before I start with the Holley conversion. My primary and idle circuits are on the rich side - idling at low 12's cold with no chock, that turned to high 11's once warmed up. Cruised at mid to low 12's on the primaries, and the secondaries with WOT actually was around 13, which is good. Now that I know I have a proper functioning AFR gauge to illustrate what's going on with my fuel mixer as I drive, I'm about ready to put the Holley on .
The other package I had come in was a set of Vette Packs from CCE for my side pipes. Yeah you guys were right: way too damn loud with open pipes! lol I loved the sound at idle, but couldn't cruise on the highway unless I wearing some earmuffs! lol Did some research and these were highly recommended. Called CCE, and the owner, Eric, picked up and was really helpful in helping me pick out the correct baffles for my sidepipes. He makes them per order, and is a small business, which I love to support a small business! These will be going on first this weekend, as they'll affect my tune, then it's Double Pumper time
I had a chance tonight to put my Vette Packs in my side pipes, and installation was pretty simple: pull side pipe off, put baffle in , bend out ends until you get the desired tension, then bolt side pipe back on. The Vette Packs themselves were excellent quality, with nice welds done by Eric. These baffles consist of one chambered part and a glass pack. The result was a quieter idle - I miss the angry open pipe idle! But the tone of the pipes when I rev it sounds so much better! I now don't need ear muffs when cruising, and the old ladies on my street won't call the cops on my, so mission accomplished! I now have everything finally finished in order to put my Holley on, so I can start that project next this weekend!
Got my Holley on this weekend and worked on dialing it in. Besides the idle mixtures, I was surprised how close this carb is with the factory tune! Had to turn the idle mixture screws in to close to half a turn, and damn they are sensitive at that point! but got my idle in the low 14's. Car cruises at 50MPH in the mid to low 13's , but when I get up to 65MPH it's in the low 12's. My assumption is the power valve is kicking in when I'm cruising at the higher RPM and enriching the mixture. I need to put a vacuum gauge on then verify. The primary accelerator pump is spot on with the orange cam. The secondary is too rich, I swapped the pink cam back in and it's still too rich, so I need to reduce my squirter size: It's currently a 31, should I go down to 29? What AFR are y'all targeting while cruising on the primaries? high 13's/low 14's is where i'd like to be and drop down to 12's with the PV.
Here's a look at how the wideband helps: can see the AFR and paint a precise picture on what's going on with the carb. You can see when I floor it , it bogs down to the 10's , which indicates that my secondary accelerator pump has too rich of a shot.
2020 Corvette of the Year Finalist (performance mods)
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YOu definitely should check and see what your power valve is and see what your vacuum is doing. I have mine around high 14 to mid 15 on a flat cruise. It gets to the high 15s and touches 16 on an incline as the power valve opens and it drops right down into the 13s. If I jump on mine it dives into the 10s, ITs a tripower so I have to change the plates to aftermarket ones that accept jets. You can look for a cam set that has a smaller ramp rate or drop to the 29s. They are easy to change so it isnt a big deal like the jets. Does it come back up after the bog? What does it do ion the highway under load when you floor it. It should act differently than just doing it in the driveway. DOnt forget you have mechanical secondairies which is just dumping fuel as soon as they open, so you could have some huge jets in there as well. I would check it on the highway and go from there
YOu definitely should check and see what your power valve is and see what your vacuum is doing. I have mine around high 14 to mid 15 on a flat cruise. It gets to the high 15s and touches 16 on an incline as the power valve opens and it drops right down into the 13s. If I jump on mine it dives into the 10s, ITs a tripower so I have to change the plates to aftermarket ones that accept jets. You can look for a cam set that has a smaller ramp rate or drop to the 29s. They are easy to change so it isnt a big deal like the jets. Does it come back up after the bog? What does it do ion the highway under load when you floor it. It should act differently than just doing it in the driveway. DOnt forget you have mechanical secondairies which is just dumping fuel as soon as they open, so you could have some huge jets in there as well. I would check it on the highway and go from there
It does immediately come back up after the bog, it's definitely the secondary accel pump. When cruising down the highway at 65 it's in the high 11's, and when I tip in the throttle it doesn't change - which seems to me like the PV is open in cruise. It's currently the 6.5 PV, so I need to take a vacuum reading and go up a couple of sizes. the WOT AFR is great - low 13/high12. I likely need to go up a few sizes on the PV, and maybe down a little on the primary jets. But the starting point isn't far off!
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
The power vavle woupld be going down as well. YOur vacuum is highest at cruise so if a 6.5 is openning you probably arent to far above 10 inches at cruise. I would look for a 5.5 or a 4.5 and tune from there. Once you get out of the power valve if you are still in the low 14s at idle and thats your best go one size smaller in your jets and you should see the idle AFR come up. If its still rich we can talk about your idle versus transition circuits an dhow your throttle screw settings affect that
If it's going rich when you get up to 65 it could be that your transitioning from your idle/midrange circuit to your mains and your mains may be to big. unlikely it's your power valve unless you have super low vacuum at 60+ mph.
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
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Good point to ponder. You should run around with a vacuum gauge hooked to manifold vacuum to see what your engine is doing. Mine is kind of tame with restrictive heads and draws 15 inches easily on the flats but any rise in the road it can see a dip to as low as 10 inches
If it's going rich when you get up to 65 it could be that your transitioning from your idle/midrange circuit to your mains and your mains may be to big. unlikely it's your power valve unless you have super low vacuum at 60+ mph.
Originally Posted by Rescue Rogers
Good point to ponder. You should run around with a vacuum gauge hooked to manifold vacuum to see what your engine is doing. Mine is kind of tame with restrictive heads and draws 15 inches easily on the flats but any rise in the road it can see a dip to as low as 10 inches
Going to put a vacuum gauge on this evening and do some cruising so I know exactly what's going on.
I ordered the below last night to have some options for tuning this week:
#67 jets to reduce primaries #77 jets if I need to go bigger on secondaries for WOT 4.5 PV #29 squirter nozzle for secondary
One other thing to check when you hook up the vacuum gauge is how low it drops at wide open throttle. on the outside chance it doesn't drop to 3 or less inches you want to make sure it drops below what your power valve is rated at. if for some strange reason it only drops to say 5" the 4.5 pv isn't going to work. you probably will not have an issue but it is easy to check while your driving.
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
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Correct, your main jets are just too big. After you change them you may have to readjust your idle circuit screws as well. Right down all your references that you told us about and change one thing at a time. Keep good records so you can go backwards of things go too lean
Got some parts in and made some adjustments today: Went from a 69 primary to a 67, it's getting closer but I still want to take a little more fuel out. Should I drop down to a 65 primary from here?
45 MPH at 2000 RPM = 13.6 AFR
65 MPH at 3000 RPM = 13 AFR
I also reduced the secondary squirter from a 31 to 29: still got a rich bog on my initial hit. What should my next adjustment be?
You can try a 65 primary jet and see how it runs. don't get super hung up on a number. you may get it to 15:1 but it may run like crap. 13:1 is not that bad. if you go to 65's and you end up close to 14:1 and it runs good then thats great but make sure it runs good and no pinging or overheating or surging or hesitation etc. not sure how you set up your idle mixture but you can tune a little with them also as they will affect your midrange and cruise up to a certain point when it transitions to the mains. not everybody sets the idle mixture this way but this is what i do: i use a vacuum gauge and adjust the mixture screws out until i get the highest vacuum reading. start with the front then the back - if you have a 4 corner idle circuit.go back and forth until you have the highest idle - turning the screws in and out in small increments. all four screws should be out the same # of turns when your done - usually you should be somewhere between 1-2 turns out from fully seated. once you are at the highest vacuum reading try turning them in just enough to barely start dropping the vacuum - maybe 1/16 to 1/8 turn in then take it out for a spin. this may lean your 45mph afr a little. but again make sure it runs good. none of the numbers mean anything if it runs terrible. you can also play with the idle air bleeds and the high speed air bleeds but hopefully you won't have to go that far.
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
Engines bog from many different reasons, too rich, too lean, not enough timing, bad timing if you are locked out, frozen distributors. I think you are going in the right direction. Go to the 65 jets on your primary side. Once thats done, go out and floor the accelerator and get an AFR number under full load. If its dumping into the 10'sthen its still too fat.... go smaller on the secondairies. Remember you have mechanical secondairies so you are getting everything when you jump on it. You have a double pumper so you also have to pay attention to the secondary side; Watch the vacuum gauge and see what happens when the power valve opens. If your jets are fat and then you dump the power valve you will be drowning the motor until the vacuum comes up and it can recover when the valve closes.
Re-adjust your timing from 34 to 36 or 38 degrees. Does our vacuum advance work. Make sure you are getting another 12 degrees on your initial setting or so when you hook it up at idle and make sure its coming of manifold vacuum
You can try a 65 primary jet and see how it runs. don't get super hung up on a number. you may get it to 15:1 but it may run like crap. 13:1 is not that bad. if you go to 65's and you end up close to 14:1 and it runs good then thats great but make sure it runs good and no pinging or overheating or surging or hesitation etc. not sure how you set up your idle mixture but you can tune a little with them also as they will affect your midrange and cruise up to a certain point when it transitions to the mains. not everybody sets the idle mixture this way but this is what i do: i use a vacuum gauge and adjust the mixture screws out until i get the highest vacuum reading. start with the front then the back - if you have a 4 corner idle circuit.go back and forth until you have the highest idle - turning the screws in and out in small increments. all four screws should be out the same # of turns when your done - usually you should be somewhere between 1-2 turns out from fully seated. once you are at the highest vacuum reading try turning them in just enough to barely start dropping the vacuum - maybe 1/16 to 1/8 turn in then take it out for a spin. this may lean your 45mph afr a little. but again make sure it runs good. none of the numbers mean anything if it runs terrible. you can also play with the idle air bleeds and the high speed air bleeds but hopefully you won't have to go that far.
Pat
My idle mixture screws are 1/2 turn out, had to do this to get idle AFR in a decent range
Engines bog from many different reasons, too rich, too lean, not enough timing, bad timing if you are locked out, frozen distributors. I think you are going in the right direction. Go to the 65 jets on your primary side. Once thats done, go out and floor the accelerator and get an AFR number under full load. If its dumping into the 10'sthen its still too fat.... go smaller on the secondairies. Remember you have mechanical secondairies so you are getting everything when you jump on it. You have a double pumper so you also have to pay attention to the secondary side; Watch the vacuum gauge and see what happens when the power valve opens. If your jets are fat and then you dump the power valve you will be drowning the motor until the vacuum comes up and it can recover when the valve closes.
Re-adjust your timing from 34 to 36 or 38 degrees. Does our vacuum advance work. Make sure you are getting another 12 degrees on your initial setting or so when you hook it up at idle and make sure its coming of manifold vacuum
My bog is currently from too rich of an initial hit on the secondary's - it drops to 10 then immediately comes back up and hauls ***! WOT pulls are in the 12.5 - 13.2 range currently.
If your WOT AFR is 12.5-13.2 you are right where you want to be, you can work on your squirters to eliminate the bog - if that is the problem. if you end up going leaner on your primary jets to get your cruise where you want it you can go richer on your secondary jets to make up for it at WOT.
