65' 365HP Vacuum Advance issues

[David K.]

Gentlemen;

Just worked on my motor with a friend, and changed out a completely blocked vacuum advance unit for a new one; from Long Island Corvette. Also adjusted the timing (10deg), and changed the sparks to NOS AC45 units.

Since the works, my engine is knocking on hard acceleration, and I cannot adjust my idle at the carb, with the vacuum connected. Idle stays at 950-1000.
Someone suggested to unhook and block the vacuum hose - and this has solved the knocking, and I can now adjust the idle down to 850 range.
NB - We removed the rotor during works & I assume we placed it back in the same position...... Lots of stuff going on & it's confusing. Are there simply adjustments to be made, or perhaps the vacuum advance unit supplied is the wrong application ? I have been told that the 'STANDARD IGNITION' VC181 unit is the proper vacuum advance for my car.

Finally, we adjusted the solid lifters to factory specs on a cold engine. The "clacking" sound is more pronounced now with the engine running. Is this ok ?

Thanks in advance;

[Terry D.]

Re: 65' 365HP Vacuum Advance issues

http://www.corvette-restoration.com/...ine_Timing.pdf Here is just one article by someone who knows. I'm assuming you meant VC1810, that appears to be correct. Lars has several articles worth reading especially if you are not a mechanic. Just google his name. You don't tell us how you adjusted the timing, also search the archives for articles on adjusting solid lifters. Also check your mail

Terry

[Duke W.]

Re: 65' 365HP Vacuum Advance issues

What do you mean by "blocked"? Was it leaking? Frozen? What about the signal line? Is it open? Does it show vacuum at idle?


What is the number stamped on the VAC mounting bracket?

Using a MityVac or equivalent, what are the stop and start points of the pin?

What is idle vacuum at 800, 900, and 1000?

Many "reproduction" VACs many have the correct OE number stamped on the bracket, but they are far off OE specs and result in poor engine operation.

Do a google search - williams hinckley corvette valve adjustment - and download the pdf from the web site lbfun, which is the lastest version, 9/2008. Also google williams san diego corvette and download the pdf of the tuning seminar.

The Standard VC177, not VC181, is a correct replacement for the original 236 16, if you can find one. Replacements, stamped B28, are getting hard to find, but recent reports say you can buy a B28 in the Airtex brand 4V1053.

The OE VAC specs are in your shop manual or AMA specs that you can download from the GM Heritage web site.

Also do some searching on the TDB - VAC vacuum advance B28... There are many threads on checking/setting up the spark advance map for various OE engine configurations. It's not hard to do. You just need some education.

Duke

[Joe C.]

Re: 65' 365HP Vacuum Advance issues

Gentlemen;

Just worked on my motor with a friend, and changed out a completely blocked vacuum advance unit for a new one; from Long Island Corvette. Also adjusted the timing (10deg), and changed the sparks to NOS AC45 units.

Since the works, my engine is knocking on hard acceleration, and I cannot adjust my idle at the carb, with the vacuum connected. Idle stays at 950-1000.
Someone suggested to unhook and block the vacuum hose - and this has solved the knocking, and I can now adjust the idle down to 850 range.
NB - We removed the rotor during works & I assume we placed it back in the same position...... Lots of stuff going on & it's confusing. Are there simply adjustments to be made, or perhaps the vacuum advance unit supplied is the wrong application ? I have been told that the 'STANDARD IGNITION' VC181 unit is the proper vacuum advance for my car.

Finally, we adjusted the solid lifters to factory specs on a cold engine. The "clacking" sound is more pronounced now with the engine running. Is this ok ?

Thanks in advance;

If you opened the lash on the valves, it will exacerbate your detonation condition. It doesn't appear that you'd understand if I tried to explain........so I won't.
Your valve lash should be @ .025/.025, warm. Initial spark advance, with vacuum advance disconnected and plugged should be 10 - 12 BTDC. 236-16 can should pull in another 16 degrees advance at idle after you connect the vacuum hose. Spark advance at 2350 RPM with vac advance disconnected should be 36 - 38 degrees BTDC, and should not advance any further if RPMs are increased.