need help
Thread Starter
Cruising
Joined: Sep 2014
Posts: 10
Likes: 0
need help
Guys I sent this thread to tadge but I have not heard back so I figured I would toss the ball to you guys.
I purchased a 1965 corvette last july and spent most of the fall and winter redoing the suspension and the interior. I replaced the inside wiring harness as well as headlight harness. The car has a 327/365 in it seems to be very strong. I keep having a miss in it. It doesn't seem to be as bad when I am accelerating through the gears but as soon as i am a constant rate of speed it starts to miss. I have replaced the original Holly four barrel with a new Holly 4160c. I replaced the distributor with a Mallory with the electronic eye (no points). replaced spark plugs twice and wires twice, the last time I put in 8mm spiral core Taylors. I set the intake valves at .020 and the exhaust at .030. The compression is at 145 on each cylinder. I still have a miss. Where would you look next?
I purchased a 1965 corvette last july and spent most of the fall and winter redoing the suspension and the interior. I replaced the inside wiring harness as well as headlight harness. The car has a 327/365 in it seems to be very strong. I keep having a miss in it. It doesn't seem to be as bad when I am accelerating through the gears but as soon as i am a constant rate of speed it starts to miss. I have replaced the original Holly four barrel with a new Holly 4160c. I replaced the distributor with a Mallory with the electronic eye (no points). replaced spark plugs twice and wires twice, the last time I put in 8mm spiral core Taylors. I set the intake valves at .020 and the exhaust at .030. The compression is at 145 on each cylinder. I still have a miss. Where would you look next?
Le Mans Master
Joined: Jan 2007
Posts: 6,011
Likes: 1,520
From: Prescott Arizona
First off, Welcome to the Corvette Forum. How about posting some pics of your 65 when you get the chance. As to the miss, the list of 'usual suspects' is probably pretty long. Other than the parts you've replaced, can you fill us in on the other things like what you're timing is set for initial timing and total timing? How did the plugs look when you pulled them? Any crud from the gas tank found in the carb when you took it off?
Mike T - Prescott AZ
Mike T - Prescott AZ
Thread Starter
Cruising
Joined: Sep 2014
Posts: 10
Likes: 0
First off, Welcome to the Corvette Forum. How about posting some pics of your 65 when you get the chance. As to the miss, the list of 'usual suspects' is probably pretty long. Other than the parts you've replaced, can you fill us in on the other things like what you're timing is set for initial timing and total timing? How did the plugs look when you pulled them? Any crud from the gas tank found in the carb when you took it off?
Mike T - Prescott AZ
Mike T - Prescott AZ
Race Director
Joined: Feb 2007
Posts: 15,500
Likes: 8,972
From: northern california
C2 of Year Finalist (track prepared) 2019
Try either dialing back the initial advance to 4 degrees or disconnecting (and plugging) the vacuum advance.
If I'm right, the "miss" you feel will go away.
Race Director
Joined: Jan 2003
Posts: 17,750
Likes: 3,735
From: Central Arkansas
Two things come to my scattered mind:
1. Plug wires breaking down seem to cause a miss at light engine load more so than during hard acceleration. You can check the wires resistance or run it at night and look for any signs of spark leakage in the engine bay.
2. Are you running vacuum advance? Sometimes an incorrect vacuum advance unit results in an over-advanced situation at cruising speed when the initial, mechanical and vacuum advance are all in play. It actually fires the engine too far in advance of TDC creating
almost a kickback or surging sensation that feels like a miss. Give it some gas and the vacuum advance will go to near 0 and the miss disappears. If this sounds familiar I would check your timing with and without the vacuum advance hooked up and see how much the vacuum pot is pulling in.
Jim brings up a good point - you may have too much initial timing and a combination of too much total timing when the centrifugal advance is all in. And then the vacuum advance compounds the issue. Do you have a dial-back timing light so you can check your total of initial and centrifugal advance when the motor is reved up to pull it all in? You probably need to have around 36 deg. total initial + centrifugal advance.
1. Plug wires breaking down seem to cause a miss at light engine load more so than during hard acceleration. You can check the wires resistance or run it at night and look for any signs of spark leakage in the engine bay.
2. Are you running vacuum advance? Sometimes an incorrect vacuum advance unit results in an over-advanced situation at cruising speed when the initial, mechanical and vacuum advance are all in play. It actually fires the engine too far in advance of TDC creating
almost a kickback or surging sensation that feels like a miss. Give it some gas and the vacuum advance will go to near 0 and the miss disappears. If this sounds familiar I would check your timing with and without the vacuum advance hooked up and see how much the vacuum pot is pulling in.
Jim brings up a good point - you may have too much initial timing and a combination of too much total timing when the centrifugal advance is all in. And then the vacuum advance compounds the issue. Do you have a dial-back timing light so you can check your total of initial and centrifugal advance when the motor is reved up to pull it all in? You probably need to have around 36 deg. total initial + centrifugal advance.
Last edited by DansYellow66; May 27, 2015 at 02:02 PM.
Race Director
Joined: Aug 2004
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From: NorCal
Just FYI - the "Ask Tadge" section is just for questions about the C7 Corvette.
Tadge Juechter is the current chief design engineer for the new Corvette and has agreed to do that occasional response to questions about the C7 Corvette only.
It's not intended as a general "Click and Clack" type of service.
Tadge Juechter is the current chief design engineer for the new Corvette and has agreed to do that occasional response to questions about the C7 Corvette only.
It's not intended as a general "Click and Clack" type of service.
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Safety Car
Joined: May 2003
Posts: 4,797
Likes: 239
From: Ocean Township NJ
327/365 is supposed to take 12-14 BTDC @ idle. As a matter of fact, that cam bleeds off so much cylinder pressure, that it will take another 5 degrees, no problems. The only way that this is too much is if the OPs engine no longer has the 30-30 cam installed.
"Too much" vacuum advance is a reach, as all diaphragms generally supply close to the same amounts. The difference is the deployment vacuum point. If the OPs engine is seeing 48-52 degrees total advance at cruise, then it is set properly.
"Too much" vacuum advance is a reach, as all diaphragms generally supply close to the same amounts. The difference is the deployment vacuum point. If the OPs engine is seeing 48-52 degrees total advance at cruise, then it is set properly.
Last edited by 65tripleblack; May 27, 2015 at 02:11 PM.
Thread Starter
Cruising
Joined: Sep 2014
Posts: 10
Likes: 0
Just FYI - the "Ask Tadge" section is just for questions about the C7 Corvette.
Tadge Juechter is the current chief design engineer for the new Corvette and has agreed to do that occasional response to questions about the C7 Corvette only.
It's not intended as a general "Click and Clack" type of service.
Tadge Juechter is the current chief design engineer for the new Corvette and has agreed to do that occasional response to questions about the C7 Corvette only.
It's not intended as a general "Click and Clack" type of service.
Thread Starter
Cruising
Joined: Sep 2014
Posts: 10
Likes: 0
327/365 is supposed to take 12-14 BTDC @ idle. As a matter of fact, that cam bleeds off so much cylinder pressure, that it will take another 5 degrees, no problems. The only way that this is too much is if the OPs engine no longer has the 30-30 cam installed.
"Too much" vacuum advance is a reach, as all diaphragms generally supply close to the same amounts. The difference is the deployment vacuum point. If the OPs engine is seeing 48-52 degrees total advance at cruise, then it is set properly.
"Too much" vacuum advance is a reach, as all diaphragms generally supply close to the same amounts. The difference is the deployment vacuum point. If the OPs engine is seeing 48-52 degrees total advance at cruise, then it is set properly.
Thread Starter
Cruising
Joined: Sep 2014
Posts: 10
Likes: 0
Two things come to my scattered mind:
1. Plug wires breaking down seem to cause a miss at light engine load more so than during hard acceleration. You can check the wires resistance or run it at night and look for any signs of spark leakage in the engine bay.
2. Are you running vacuum advance? Sometimes an incorrect vacuum advance unit results in an over-advanced situation at cruising speed when the initial, mechanical and vacuum advance are all in play. It actually fires the engine too far in advance of TDC creating
almost a kickback or surging sensation that feels like a miss. Give it some gas and the vacuum advance will go to near 0 and the miss disappears. If this sounds familiar I would check your timing with and without the vacuum advance hooked up and see how much the vacuum pot is pulling in.
Jim brings up a good point - you may have too much initial timing and a combination of too much total timing when the centrifugal advance is all in. And then the vacuum advance compounds the issue. Do you have a dial-back timing light so you can check your total of initial and centrifugal advance when the motor is reved up to pull it all in? You probably need to have around 36 deg. total initial + centrifugal advance.
1. Plug wires breaking down seem to cause a miss at light engine load more so than during hard acceleration. You can check the wires resistance or run it at night and look for any signs of spark leakage in the engine bay.
2. Are you running vacuum advance? Sometimes an incorrect vacuum advance unit results in an over-advanced situation at cruising speed when the initial, mechanical and vacuum advance are all in play. It actually fires the engine too far in advance of TDC creating
almost a kickback or surging sensation that feels like a miss. Give it some gas and the vacuum advance will go to near 0 and the miss disappears. If this sounds familiar I would check your timing with and without the vacuum advance hooked up and see how much the vacuum pot is pulling in.
Jim brings up a good point - you may have too much initial timing and a combination of too much total timing when the centrifugal advance is all in. And then the vacuum advance compounds the issue. Do you have a dial-back timing light so you can check your total of initial and centrifugal advance when the motor is reved up to pull it all in? You probably need to have around 36 deg. total initial + centrifugal advance.
Safety Car
Joined: May 2003
Posts: 4,797
Likes: 239
From: Ocean Township NJ
Unless you can identify your engine's configuration, you'll be spitting into the wind while trying to optimize distributor setup.
If all 8 plugs are not fouled, then chances are that you're not chasing a misfire. Since you're running blind, the only thing you can do is back out timing 2 degrees at a time until the surging goes away.
PS: If you give us the idle vacuum at 800 RPM, we can guesstimate which cam is in your engine.
Melting Slicks
Joined: Apr 2006
Posts: 2,331
Likes: 61
From: Sunnyvale CA
Race Director
Joined: Jan 2003
Posts: 17,750
Likes: 3,735
From: Central Arkansas
Well, it's an issue with aluminum head BB cars. The maximum vacuum advance I can run without missing at cruise is 8 degrees max on top of combined 36 degree initial and centrifugal. I had to modify my vacuum can to limit it to that. Maybe it's not an issue with SB motors but you never know what aftermarket suppliers and rebuilders are throwing into distributors without checking them out.
Thread Starter
Cruising
Joined: Sep 2014
Posts: 10
Likes: 0
You have to be more accurate when you tell us what you have. In your case, then, it is no longer a "327/365".
Unless you can identify your engine's configuration, you'll be spitting into the wind while trying to optimize distributor setup.
If all 8 plugs are not fouled, then chances are that you're not chasing a misfire. Since you're running blind, the only thing you can do is back out timing 2 degrees at a time until the surging goes away.
PS: If you give us the idle vacuum at 800 RPM, we can guesstimate which cam is in your engine.
Unless you can identify your engine's configuration, you'll be spitting into the wind while trying to optimize distributor setup.
If all 8 plugs are not fouled, then chances are that you're not chasing a misfire. Since you're running blind, the only thing you can do is back out timing 2 degrees at a time until the surging goes away.
PS: If you give us the idle vacuum at 800 RPM, we can guesstimate which cam is in your engine.
Safety Car
Joined: May 2003
Posts: 4,797
Likes: 239
From: Ocean Township NJ
Your idle vacuum at 800 will be about 9-10 in-hg, depending on your valve lash. Set your lash to .018"/.025", engine "warm".
Team Owner
Joined: Oct 2000
Posts: 38,897
Likes: 1,927
From: Washington Michigan
Safety Car
Joined: May 2003
Posts: 4,797
Likes: 239
From: Ocean Township NJ
327s I have had with the 30-30 developed about 8 when lashed at .025/.025 and 9 when lashed at .030/.030.
These are at an 800 RPM idle. Yours can apply at 1000 RPM idle.