lean AFR at light cruise
Thread Starter
Le Mans Master
Joined: May 2007
Posts: 5,029
Likes: 1,120
From: North tonawanda NY
lean AFR at light cruise
AFR goes lean at light cruise (15.1) on my quick fuel 680 VS HR carb. Ive got the idle slightly fattened to help around 13.8 to 1 and it goes pretty rich when accelerating (down in 12 to 1 range and stays in the 12-13 to 1 range while into the throttle.) Ive tried cracking the secondary blades which just made other issues at the time but I also had some weird behavior that strangely cleared up on its own(think I had some contamination in the carb) so I may give it another shot if theres any benefit? not sure what else to try? it runs great right no with no hesitation but seeing the 15 to 1 range on the afr at light cruise makes me worry. should I be? I just put in some larger 205/64cc ebay heads I build and was expecting the jetting to change but not sure theres much I can do on that front or is there? fuel pressure is adjusted to 6-7psi and floats are half way in the glass this carb does have the 4 corner idle screws and air bleeds if it helps..
Ebay heads are a noticeable improvement power wise to the iron eagle 180s they replaced. ti also runs/ idles better than it has since before I swapped the cam for a roller last summer so I think I had a vac leak since then.
Ebay heads are a noticeable improvement power wise to the iron eagle 180s they replaced. ti also runs/ idles better than it has since before I swapped the cam for a roller last summer so I think I had a vac leak since then.
Drifting
Joined: Feb 2015
Posts: 1,440
Likes: 1,031
From: Baton Rouge Louisiana
AFR goes lean at light cruise (15.1) on my quick fuel 680 VS HR carb. Ive got the idle slightly fattened to help around 13.8 to 1 and it goes pretty rich when accelerating (down in 12 to 1 range and stays in the 12-13 to 1 range while into the throttle.) Ive tried cracking the secondary blades which just made other issues at the time but I also had some weird behavior that strangely cleared up on its own(think I had some contamination in the carb) so I may give it another shot if theres any benefit? not sure what else to try? it runs great right no with no hesitation but seeing the 15 to 1 range on the afr at light cruise makes me worry. should I be? I just put in some larger 205/64cc ebay heads I build and was expecting the jetting to change but not sure theres much I can do on that front or is there? fuel pressure is adjusted to 6-7psi and floats are half way in the glass this carb does have the 4 corner idle screws and air bleeds if it helps..
Ebay heads are a noticeable improvement power wise to the iron eagle 180s they replaced. ti also runs/ idles better than it has since before I swapped the cam for a roller last summer so I think I had a vac leak since then.
Ebay heads are a noticeable improvement power wise to the iron eagle 180s they replaced. ti also runs/ idles better than it has since before I swapped the cam for a roller last summer so I think I had a vac leak since then.
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
Even light detonation at light cruise is not damaging and was common place for carbed vehicles prior to sensors being used to retard timing.
you could even go to 17:1 at light cruise. Somewhere in the 18:1 leads to misfire.
you could even go to 17:1 at light cruise. Somewhere in the 18:1 leads to misfire.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Is my vette stock?? HAHA
Joined: Oct 2015
Posts: 20,221
Likes: 9,359
From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
You can go into high 15 easily as long as you dont get pinging. At cruise yo should see your highest vacuum at the manifold due to this eing the highest efficiency and lightest load on the engine. Once you start climbing a shallow incline you would seethe vaccum dropping slightly and your afr should go leaner. This is where you start to see the power valve openning as you get into a steeper hill and you dont down shift so the load increases, the vacuum drops and eventually the power valve opens to allow in more fuel to compensate for the lean condition. My big block is plenty torquey so I dont down shoft from fifth at all on the highway and I get to 16 before my valve opens. no issues at all. I was going to drop the power valve to keep in the lower 15s but some research dropped that idea
Thread Starter
Le Mans Master
Joined: May 2007
Posts: 5,029
Likes: 1,120
From: North tonawanda NY