Another timing question - vacuum advance

After my new carb and the huge jets messed up my spark plugs I installed new plugs and set the timing yesterday. The engine seems to run great at 14-16 degrees initial timing with vacuum disconnected and plugged.
Timing seems to advance with vacuum to more than 34 degrees.... I'll have to get a balancer tape or add a few more marks to get more accurate numbers, I'll also have to get someone to look at the tach so I know the rpm....

The vacuum line is connected to ported vacuum on the carb.

So far I have not heard pinging.

I'll do some more 'testing' today. Time to read Lars' papers again.... :noworry:

First, read my current papers on how to set things up. Current papers are only available by e-mailing me for copies:
[email protected]

But here's the Reader's Digest version:

First, don't use ported vacuum unless you're trying to pass an emissions test. Run the vacuum advance off of a manifold vacuum port.

Next, the amount of vacuum advance you get is all dependent on the vacuum advance control unit you're using. Use a unit outlined in my papers that does not pull in any more than 16 degrees (8 distributor degrees) of advance.

With this done, set total timing to 36. Once set at 36, initial will hopefully be in the 14-18 degree range. When you plug your vacuum advance in, this should then pull the idle timing up to about 30-36 degrees, which is perfect.

Get with me on any questions.

Lars

Lars, where the hell were YOU when I was frustrated and dicking around with old form HEI's on various cars, decades ago???

:twitch::sos:

all my shit is computer now, except my work truck,

:surrender:

Lars, I read in your paper that the AR12 is pretty much what I need. Where can I buy it ? When I google AR12 it comes up with all sorts of stuff but no stores... a Summit search returned a spark plug but no vacuum can...

New problem: it runs great in neutral but as soon as I hit the throttle in gear and want to accelerate it misfires at around 2500rpm....

I am not sure if this is a carburetor or ignition problem.

I am at a point where I think I should have left it alone, it was running ok with the old performer intake and 600cfm carb....:tth:

MYBAD79 said:

Lars, I read in your paper that the AR12 is pretty much what I need. Where can I buy it ? When I google AR12 it comes up with all sorts of stuff but no stores...

Click to expand...

AR-12= VC1838

NAPA
Autozone

Usually takes 24 hours to get.

Just throw the vac can in the trash,and don't worry about it anymore :wink:
You don't need one.

big2bird said:

AR-12= VC1838

NAPA
Autozone

Usually takes 24 hours to get.

Click to expand...

They have the spring kit MRG-928G but the vacuum can is DV1838, not VC1838... think that's the same ?? I am guessing that the D stands for Duralast (that's AutoZone's brand)...

kwplot34 said:

Just throw the vac can in the trash,and don't worry about it anymore :wink:
You don't need one.

Click to expand...

I'm getting ready to throw more than just the vac can in the trash.... :cussing:

I won't be working on it until next weekend, that's hopefully enough time to cool off....

The DV1838 is the same as the VC1838. It's the same brand. Just different box (there is only one manufacturer of the vacuum advance control units).

If your timing is correctly set (regardless of vacuum advance) and you still have the problem, you likely have a carb issue. Why don't you just swap a different carb onto the car and try it out?

Lars

MYBAD79 said:

kwplot34 said:

Just throw the vac can in the trash,and don't worry about it anymore :wink:
You don't need one.

Click to expand...

I'm getting ready to throw more than just the vac can in the trash.... :cussing:

I won't be working on it until next weekend, that's hopefully enough time to cool off....

Click to expand...

I would bet money that you will get it figured out,i am sure it's something simple, it's always the easy things that give the most problems.

And if i may ask a quick question with out hijacking the thread to much.

Lar's. if i am running race fuel 110 oct, how much extra advance can you run,and how do you know when you have reached the limit for best performance?

Most V8 engines will develop peak torque (and power) at 36 degrees total timing, plus or minus 2 degrees. You only need high octane fuel if you cannot obtain this setting without detonation. Adding additional timing beyond this point will not produce more power, with or without the race gas.

You can tell if you've reached the performance limit in one of two ways:

1. Put the engine on a dyno and try out the total timing points.
2. Run the car on the strip and set timing for maximum mph through the traps.

Every engine I've worked on has produced best numbers with total timing between 34 and 38 degrees, regardless of octane used (as long as detonation was suppressed).

Lars