Adjustable vac advance for Chevy L6 distributor

[Carl Spangler]

Greetings

Does anyone make an adjustable vacuum advance for a stock Chevy L6 distributor? I've looked at all the usual suspects and can't find one that is similar to the one shown below.

Notice the hook shaped arm: I annotated the image to indicate where an adjustable stop might possibly be added.


Worst case scenario would be to fabricate an adjustable stop near the canister-arm interface per the pic above.

[geezer#99]

I've seen them for hei's but not for a six.
Curious!!
Why do you need to limit it?

[Carl Spangler]

Originally Posted by geezer#99

I've seen them for hei's but not for a six.
Curious!!
Why do you need to limit it?

Too much vac advance at idle/low speed.

[RichardJ]

A stop there will limit Total vacuum advance, but it won't change the amount of vacuum needed for vacuum to begin the advance.

>>Too much vac advance at idle/<<

If you are having vacuum advance at idle, the idle rpm is too high and/or the carb isn't adjusted properly. Have you checked for vacuum leak? What is base timing?

[VWNate1]

! You have the dizzy vacuum hose connected to the wrong carby port ~ if you do simple testing you'll find a vacuum port with ZERO VACUUM @ IDLE BUT IT'LL BEGIN PULLING VACUUM THE *INSTANT* YOU OPEN THE THROTTLE .

This is very important on i6 engines to give proper idle and max power right off idle .

Remember to re set the base timing @ 700> RPM after you've corrected this vacuum mistake and be amazed at how much power you gained whilst still being buttery smooth and not run hot .

[Carl Spangler]

Originally Posted by VWNate1

! You have the dizzy vacuum hose connected to the wrong carby port ~ if you do simple testing you'll find a vacuum port with ZERO VACUUM @ IDLE BUT IT'LL BEGIN PULLING VACUUM THE *INSTANT* YOU OPEN THE THROTTLE .

This is very important on i6 engines to give proper idle and max power right off idle .

Remember to re set the base timing @ 700> RPM after you've corrected this vacuum mistake and be amazed at how much power you gained whilst still being buttery smooth and not run hot .

I'm using manifold vacuum for the advance. The ported vacuum doesn't retard timing enough at cruise-light load. i.e. ping city.

[RichardJ]

It's called a vacuum advance for a reason.

>>The ported vacuum doesn't retard timing enough <<

Using a vacuum advance for an off-idle vacuum retard is a Band-Aid for incorrect timing and poorly adjusted carb.

There is no reason to set a stock six cylinder idle above 600. Depending on engine condition, oil pressure can drop off too much as it gets closer to 500.

[VWNate1]

I know you're frustrated here Carl but it was designed to run best on ported vacuum, you're forcing it to ping using manifold vacuum .

Once you try the correct way you'll see and we can set about fine tuning it for max power and economy both .

I;m a Geezer who grew up working on/with i6 powered farm machines long before your truck was designed much less built, one thing I know is how to tune InLine engines .

I wish I was closer (and not in this wheelchair) as I could do it for you before lunch .

[Carl Spangler]

All's good:

The dwell was way off. Once that was set correctly (and timing adjusted) the old 6 is running great. Thanks for all of the suggestions and offers of help. I'm going to leave the vac advance on the manifold for now as it's running really well under a variety of load conditions.

Note: This engine has always had part throttle ping issues when using the ported vac line.