Testing "Capt. Shark's" Carb Problems
Thread Starter
Tech Contributor
Joined: Aug 1999
Posts: 14,379
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
Dennis -
Are you talking that the car ran "perfect before they installed the new cam," or what is "before?" (Before I rebuilt the carb, before Covid-19; before Dorothy left Kansas....?)
Have you tried "cupping" you hand over the choke tower to artificially induce a rich condition to see if this will make it smooth out or idle below 1000 rpm? If the cam they installed is pulling extremely poor manifold vacuum, it will cause the carb to lean out at idle due to poor manifold vacuum fuel signal to the idle circuit. But a cam has to be pretty damned radical to be pulling less than 10 inches of vacuum at 1000 rpm idle - that's down in L88 territory... In my own street car, I'm running a solid roller that's pretty rough (280/286 advertised, compared to your 270 advertised), and I'm pulling 12 inches at 950 rpm idle here at 5500 feet elevation. Something is just plain wrong with the engine assembly... a 270 cam does not idle at 10 inches at 1000 rpm, no matter what carb is on it.
Lars
Are you talking that the car ran "perfect before they installed the new cam," or what is "before?" (Before I rebuilt the carb, before Covid-19; before Dorothy left Kansas....?)
Have you tried "cupping" you hand over the choke tower to artificially induce a rich condition to see if this will make it smooth out or idle below 1000 rpm? If the cam they installed is pulling extremely poor manifold vacuum, it will cause the carb to lean out at idle due to poor manifold vacuum fuel signal to the idle circuit. But a cam has to be pretty damned radical to be pulling less than 10 inches of vacuum at 1000 rpm idle - that's down in L88 territory... In my own street car, I'm running a solid roller that's pretty rough (280/286 advertised, compared to your 270 advertised), and I'm pulling 12 inches at 950 rpm idle here at 5500 feet elevation. Something is just plain wrong with the engine assembly... a 270 cam does not idle at 10 inches at 1000 rpm, no matter what carb is on it.
Lars
Last edited by lars; Apr 22, 2020 at 10:22 PM.
Team Owner
Joined: Jan 2006
Posts: 39,388
Likes: 171
From: Into the Mystic And yet, despite the look on my face, you're still talking TN
St. Jude Donor '09 thru '25
Lars,
The car ran perfect when I left it at the shop for the cam and heads install. I did try the cupping hand before and it just choked the engine. I will try that again today.
As you say, there is something just plain wrong with the engine assembly. I wonder if I will ever get any satisfaction from the shop? So far I have not talked to them, but this morning I will.
Before I do though, I will talk to Lunati's tech people for some more ammo.
Good grief.
The car ran perfect when I left it at the shop for the cam and heads install. I did try the cupping hand before and it just choked the engine. I will try that again today.
As you say, there is something just plain wrong with the engine assembly. I wonder if I will ever get any satisfaction from the shop? So far I have not talked to them, but this morning I will.
Before I do though, I will talk to Lunati's tech people for some more ammo.
Good grief.
Melting Slicks
Joined: Apr 2001
Posts: 3,399
Likes: 278
From: Olmsted Falls, Ohio
Back to an engine problem. Maybe even a wiped cam, lifters, rockers, mouse trapped in cylinder, who knows.
BUT the shop will give you the "it was good when it left here" spin. And by your own admission, it was BEFORE they worked on it. But how was it when you got it back from them?
Whatever the outcome, you will be spending more money, just don't spend it there!
Reading threads on this forum is like listening to the 6 o'clock evening news. Nothing good there.
BUT the shop will give you the "it was good when it left here" spin. And by your own admission, it was BEFORE they worked on it. But how was it when you got it back from them?
Whatever the outcome, you will be spending more money, just don't spend it there!
Reading threads on this forum is like listening to the 6 o'clock evening news. Nothing good there.
Last edited by KenSny; Apr 23, 2020 at 09:17 AM.
Team Owner
Joined: Jan 2006
Posts: 39,388
Likes: 171
From: Into the Mystic And yet, despite the look on my face, you're still talking TN
St. Jude Donor '09 thru '25
It ran like crap when I picked it up from then. The timing was jacked up, they had the carb all out of whack. They gave me the carb bs and I honestly thought I could get it home and straighten it out.
They had it forever and I guess I was just ready to be done with them. My mistake. And you are correct about it costing me even more money. Just not sure now where to take it to get it straightened out.
They had it forever and I guess I was just ready to be done with them. My mistake. And you are correct about it costing me even more money. Just not sure now where to take it to get it straightened out.
Team Owner
Joined: Jan 2006
Posts: 39,388
Likes: 171
From: Into the Mystic And yet, despite the look on my face, you're still talking TN
St. Jude Donor '09 thru '25
I may, emphasize may, have this thing figured out. I hit each header tube with my infrared temp gun and #5 cylinder was much lower temp on initial start up. Long story but I think it's a bad plug wire. #5 plug was also fouled. Very weak spark and the engine runs the same whether the wire is connected to the plug or not. Seven out of eight ain't so good, is it? Does it sound like this may be my problem?
Lordy, I sure hope I've got this figured out.
Lordy, I sure hope I've got this figured out.
Thread Starter
Tech Contributor
Joined: Aug 1999
Posts: 14,379
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
"90% of all carb problems are ignition problems."
My opening statement from my "Tuning for Beer World Tour" tuning seminars (23 tours & seminars conducted across the U.S. and Europe over 5 years).
Lars
My opening statement from my "Tuning for Beer World Tour" tuning seminars (23 tours & seminars conducted across the U.S. and Europe over 5 years).
Lars
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
Pro
Joined: Nov 2021
Posts: 562
Likes: 277
From: Arvada Colorado
Stalling
I just went through a situation like this with my 62. 327/340 AFB 3269S. It was carburetor percolation due to the carb getting too hot. I had block my exhaust heat riser ports with fuel injection intake gaskets. Then I added a 1/2” phenolic spacer under the carb. These two cooled down the carb considerably. The other thing I did was I added a small electric pump on the suction side of my mechanical pump for vapor lock. I am at 5300 feet here in Colorado and vapor lock is an issue. I also should add that my car has a new fuel tank, sender, fuel suction lines, fuel pump and rebuilt carb. The hot die off has been an issue with this thing since I got it in 2021. Now the problem is gone.
Pro
Joined: Nov 2021
Posts: 562
Likes: 277
From: Arvada Colorado
