10:1 AFR at WOT

[Ravage]

...If the car is good on part throttle acceleration...

... if the power valve is coming in early, you could put a lower number power valve in there to delay the power valve a bit...

...Depends on how big your cam is and what your vacuum looks like...

Thank you for all the information. I've always been scared of messing with carburetors because there are so many little springs and screws that affect everything. Gotta love the internet. At part throttle accel. the engine does about as well as can be expected for a mild 318. I have a couple lower number power valves on the way from Summit as we speak. I don't recall my cam specs ( I really should keep a little notebook of these things) but it is a little more aggressive than stock. A vacuum gauge is also on the way. Between the AFR, the vacuum gauge, and the power of the internet I hope to have it running like a top before the weekend is over

 

[Strawdawg]

I would certainly use the spring chart above and see what spring is currently in the vacuum secondary diaphragm unit

[Ravage]

Update:  Vacuum is reading 10-11 in gear at idle warm. Popped in the 5.5 power valve and went for a spin around the neighborhood. Couldn't do much testing because I keep hearing sirens from the cops doing speed patrol on the main streets and I don't want to drive like too much of an a-hole in residential, but if there was an improvement it wasn't very perceptible ( I did have the air cleaner off, not sure how much impact that would have). Ordered secondary spring kit from Summit. The Medium spring is in there now (love that quick change design).

Also have 4.5 power valve sitting on workbench (ordering extra parts is cheaper than paying multiple shipping/handling fees). May swap that in depending how the springs treat me.

[Chryco Psycho]

If you have 11" Vacuum at idle in gear the 5.5 will not affect much as you found out but that eliminates 1 problem 
 Secondary spring would be my next change , make sure the floats are set correctly too .

[stinger]

I don't see how the secondary spring is gonna cure a rich condition @ WOT. nor do I see a problem with a 6.5 powervalve.
But the only facts I've caught is it's a 318 with a performer rpm intake. what cam,heads,trans,gear, etc.etc?
an AFR gauge and numbers isn't gospel,it's a tool to figure out how to tune to Your car. carbs are not perfect all the time either. my vote it to drop the size of the jets 2 sizes and see. maybe 4. maybe you need a 750?

[Ravage]

If you have 11" Vacuum at idle in gear the 5.5 will not affect much as you found out but that eliminates 1 problem 
 Secondary spring would be my next change , make sure the floats are set correctly too .

That's how I see it, getting closer to a solution 

I don't see how the secondary spring is gonna cure a rich condition @ WOT. nor do I see a problem with a 6.5 powervalve.
But the only facts I've caught is it's a 318 with a performer rpm intake. what cam,heads,trans,gear, etc.etc?
an AFR gauge and numbers isn't gospel,it's a tool to figure out how to tune to Your car. carbs are not perfect all the time either. my vote it to drop the size of the jets 2 sizes and see. maybe 4. maybe you need a 750?

I can't recall the cam specs. just that the grind is little more aggressive than stock. Stock heads     3 speed 727 and 3.23 rear end. Pistons are 0.060 over. Everything else is pretty dern stock.

[YellowThumper]

I don't see how the secondary spring is gonna cure a rich condition @ WOT. nor do I see a problem with a 6.5 powervalve.
But the only facts I've caught is it's a 318 with a performer rpm intake. what cam,heads,trans,gear, etc.etc?
an AFR gauge and numbers isn't gospel,it's a tool to figure out how to tune to Your car. carbs are not perfect all the time either. my vote it to drop the size of the jets 2 sizes and see. maybe 4. maybe you need a 750?

Too weak a spring the secondaries drop open too soon. As it is rich now with a bog it takes time for the engine to fully recover.

[1 Wild R/T]

Too weak a spring the secondaries drop open too soon. As it is rich now with a bog it takes time for the engine to fully recover.

But since it's vacuum secondaries there is no second accelerator pump to fatten the mixture, theres to much air available so theres no velocity so no fuel is drawn through the boosters & while the power valve will be open due to the low vacuum again no velocity so no flow....     Accelerator pump & circuit is where the OP needs to be looking...

As was covered earlier if the rich condition persisted past the first hit of the throttle you'd be looking at jetting & power valve but the initial snap of the throttle is masked by the accelerator pump...

 

[Ravage]

A lot of my carb was set up to the point of running smooth without much prior tweaking. Would I want to loosen or tighten the spring on the accelerator pump? The vacuum does increase on throttle input, I expect.there will be a lot of getting things.to play nice together.

[Ravage]

UPDATE: Got home from work and the secondary springs had arrived. Tossed in the stiffest one. It's no power house but the engine doesn't seem to hesitate anymore. Still dropping to around 11 on the AFR and second gear hits with a punch. I'd say it's about 85-90% there. Just lots of adjustments and test drives to dial it in I think. Next on the list is checking the floats and accelerator pump.

[Strawdawg]

what size is the accelerator pump nozzle?  Also might want to look at the accelrator pump cam and see which one is in there and what hole it is installed on.  thinking about prolonging the pump spray a bit and/or going to a smaller nozzle depending upon what is in there.

[Chryco Psycho]

A lot of my carb was set up to the point of running smooth without much prior tweaking. Would I want to loosen or tighten the spring on the accelerator pump? The vacuum does increase on throttle input, I expect.there will be a lot of getting things.to play nice together.

venturi / ported vacuum should increase with rpm , manifold vac should drop .
the spring on the accelerator pump arm needs to be long enough so there is no play between the arm & lever , extra length  can limit travel , so you want it  short as possible  without play .

[stinger]

What about your timing?

[Ravage]

What about your timing?

I hooked up a timing light but didn't see a timing mark on the balancer. That's another issue I need to address. Much of my engine is just tuned by ear and adjustments while driving. Been driving that way for years, even put 800 miles on it for Carlisle without a single issue  but this is the year of the great tuning.

[stinger]

timing and fuel go hand in hand,can't do one without the other. you can easily static time it and mark your balancer. I would do this first.