Tuning an Edelbrock 650AVS on a stock 340

[RustyRatRod]

I’ll likely dial it back to 20 it was fighting the starter hot) but I’ll have 40 total then.

Yeah you need to limit total to 34-36.

 

[1MeanA]

Going to the lighter springs was a fail as the AFRs dropped. Easy fix.

 

[Bewy]

Mean,
My GTO left the showroom floor with 26* initial timing. 6* init + 20* added from man vac adv. Small factory cam 197 @050 10.75:1 CR. So 25* does not surprise me. My engine has a smooth idle in gear, 800 rpm, & 48* at idle. Yes, 48*, not a misprint!

The best way to get the extra idle timing is with an ADJUSTABLE vac adv unit connected to man vacuum [ MVA ]. MVA is mentioned in the Edel owners book.
If you use 12* init, you can add 23-24* with MVA. You will likely need to make a stop for the VA actuator, but this is what hot rodding is all about....

 

[1MeanA]

Mean,
My GTO left the showroom floor with 26* initial timing. 6* init + 20* added from man vac adv. Small factory cam 197 @050 10.75:1 CR. So 25* does not surprise me. My engine has a smooth idle in gear, 800 rpm, & 48* at idle. Yes, 48*, not a misprint!

The best way to get the extra idle timing is with an ADJUSTABLE vac adv unit connected to man vacuum [ MVA ]. MVA is mentioned in the Edel owners book.
If you use 12* init, you can add 23-24* with MVA. You will likely need to make a stop for the VA actuator, but this is what hot rodding is all about....

That is something to think about. It would remove the need to limit total mechanical advance which I would need to do with 20 or 25 degrees of initial. I did unintentionally have it hooked up to manifold vacuum and it ran ok. Is the vacuum the same as ported once the blades open?

 

[Bewy]

Yes.

 

[1MeanA]

Ok I drove with ported and with manifold vacuum. I think I will go with the manifold vacuum at 25 degrees total at idle. It was bucking very slightly in the low rpms with the ported vacuum. Other than that the car runs and drives nice either way.

Onto the next issues....

• idle rpm is often 100-300 rpm higher when I get back from a drive. Unplugging the vac advance (manifold) hose brings it down to where it is supposed to be.
• AFR is low 12s on light cruise and lean on tip in/light acceleration (15+) but it drives fine...no hesitation or bog. I'll try and enrichen the power side.

 

[AJ/FormS]

idle rpm is often 100-300 rpm higher when I get back from a drive. Unplugging the vac advance (manifold) hose brings it down to where it is supposed to be.

In my 367, I run a Hughes/Engle, 276/286/110 (230/237 @050, with 549/571 lift @ 1.6 arms); in at not more than 2* advanced per 20 years ago, and usually at 12>14* Idle-Timing.
But she'll pull nicely down to 5*advanced, and idle down to 550 in gear and pulling itself ...... like in a parade.
The only way to drive a 4-speed slow, without drama, is to retard the timing. So, I installed a dash-mounted, electronic timing module, adjustable in a range of 15*. I have it set to be able to add up to 6* advance, or retard up to 9*. It is a very handy tool.

 

[Bewy]

Mean.
Considering the combo, 25* at idle, as you have discovered is ideal, & about what I would expect with years of experience doing this.....

Idle rpm varying. Make sure the VA plate inside the dist moves freely. Is it an adj VA unit? Also make sure the centri weights move freely. The VA can have 25-30* of advance. How did you get 25* for idle? Combination of init +MVA?
How much idle vac now with 25* at idle?

 

[1MeanA]

Mean.
Considering the combo, 25* at idle, as you have discovered is ideal, & about what I would expect with years of experience doing this.....

Idle rpm varying. Make sure the VA plate inside the dist moves freely. Is it an adj VA unit? Also make sure the centri weights move freely. The VA can have 25-30* of advance. How did you get 25* for idle? Combination of init +MVA?
How much idle vac now with 25* at idle?

I took it out, warmed it up and got 5 degrees no VA and 23 degrees total with manifold VA at idle. Obviously I don't have enough mechanical advance like this and I got some light hesitation on heavier acceleration. The distributor is a new Mancini unit with adjustable VA. Its still running fat at cruise and lean on heavy acceleration. Metering rod changes don't seem to be making significant changes and there is no combo of rods and jets that will address the issue so I'm going to try heavier springs and see if that moves things the right way. Manifold is only 10 -12 inches of vacuum at 700 rpm which concerns me. I had it up to 14 inches at one time somehow. At cruise its 15 inches. The idle rpm jumped 100 once it got hot. Tuning sure has been problematic as there is some issue I don't yet understand. If I don't get it sorted before the temps drop and the snow flies I will pull the distributor this winter.

 

[Bewy]

If you are using a stock VA unit, there is no way that it will fully deploy with 10-12" of vac. [ An adj unit is reqd, with Allen Key adjusted fully CW ] . What is happening now is a whole of of new problems, caused by the VA unit causing erratic timing.

Forget about the centri curve in the dist. That is the LAST thing you do, not the first.

Try this, it is simple. Disconnect & plug the VA. Adjust timing [ turn dist ] for ~25* of timing [ so engine will have 25* initial timing ]. Re-adjust idle mixture screws. Test drive; you may get pinging for this test, that is ok.

 

[1MeanA]

...Try this, it is simple. Disconnect & plug the VA. Adjust timing [ turn dist ] for ~25* of timing [ so engine will have 25* initial timing ]. Re-adjust idle mixture screws. Test drive; you may get pinging for this test, that is ok.

I did a test drive with it set-up that way a few days ago. It was fine cruising. Today I am going to check fuel pressure as I am wondering if it is too high. (Carter mechanical pump)

 

[1MeanA]

I fixed the fuel pressure and distributor which didn't change the AFRs much. The car runs and drives pretty good. AFRs are about the same...about 1 point too rich at very light throttle, a half point too rich at heavier cruise and lean at tip in. Also, the idle rpm jumps at few hundred rpm when the engine is fully warm. I'm back to 17 degrees initial with VA ported. I'm a bit of a tinkerer. If I didn't have an AFR meter I would be happy with it apart from the high idle although I have done no tuning at WOT. I think I will start with some easy changes to see what happens:

• I think I need the one step lighter spring to enrichen the mixture earlier (pink)
• drop the float level
• downsize the primary jet to a leaner combo (I now see that the Edelbrock tuning chart doesn't give you all the rod/jet combos - got an Excel spreadsheet started to calculate the areas). I'll likely need a smaller power rod diameter to cure the lean tip unless the lighter spring cures that
• If all else fails the person that wrote this article seems to know what they are doing.

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