Holley 715 CFM #3259 float level adjustment

[67350#1242]

Can the metering block be ultrasonic cleaned without removing the caps?

[shelbydoug]

Can the metering block be ultrasonic cleaned without removing the caps?

With the Holley metering block, I'm still learning. I don't think so because what pics that I seen from Drew on the emulsion tubes, they look more like they are aluminum and have oxide corrosion on them?

Those have minimal effects on the idle circuit and even so, the main circuit is leaner then the idle circuit is.

I'd actually be leaning towards replacing them with new ones if possible.


Having said that though, rich idle issues seem to be the predominant problem. If the idle restrictions and air bleeds are clear then the most likely is the fuel level is too high or the power valve is leaking?

There is no other source of fuel to the engine.

Is it possible that the seats on the idle screws are worn out and damaged?

[csxsfm]

Are there any replacement options for the 3259 metering blocks other than eBay junk?

[Drew Pojedinec]

Yes they can be cleaned ultrasonically, but it's impossible to see or visually inspect.

I wouldn't consider even a rebuild without cleaning the idle feed by removing the cup plug.
I buy them by the 1,000@$.016 each so not worth leaving them.

[shelbydoug]

Yes they can be cleaned ultrasonically, but it's impossible to see or visually inspect.

I wouldn't consider even a rebuild without cleaning the idle feed by removing the cup plug.
I buy them by the 1,000@$.016 each so not worth leaving them.

I can report positive vibes on that one. It makes you feel like you accomplished something important and very sophisticated and advanced.

Do it. It's easy but don't try to remove the idle emulsion tube like I did, because there isn't one. 

[Drew Pojedinec]

If removing and replacing a cup plug is sophisticated or advanced, we might need to hide your drill bits from you 😂

[shelbydoug]

If removing and replacing a cup plug is sophisticated or advanced, we might need to hide your drill bits from you 😂

I use a pin vise for brain surgery. A frontal lobe lobotomy procedure. Leaves an almost invisible scar. It's very sophisticated.

It's similar to removing the metering block plug except you need to get the patient very drunk so they don't notice.

[Helmantel]

Well, after a long break I finally got back at tuning the Holley. Last year I already installed some bowl sight plugs and had adjusted the float levels a bit below the bottom of the hole (which is the normal rule of thumb setting). But that didn't make any difference.

This time, I took Drew's advice and popped out the idle well plugs. Everything was nice and clean in there, but these carbs have the idle feed restrictors hidden in this well. Measuring their size with a 1 mm drill showed that they were probably ~0.041". I had no idea if that was big or small, but some googling showed that a normal size for a ~750 cfm Holley is in the low .030 range. In combination with my mild roller cam (and thus extra high vacuum), this was probably the reason for the rich transition circuit.

I stuck in some small wires and made some new caps out of aluminum (I didn't have any brass ones). That leaned out the transition circuit somewhat from 10 to 11.5 and thus not nearly enough. At cruising speeds, the AFR creep up somewhat but dropped back to 12 right away due to the power valve. Looking at the vacuum gauge during driving, I concluded that the 8,5" power valve kicked in way too soon. I then installed a 6,5" PV which allowed the AFR creep up to 14, but the power valve still kicked in too soon, especially in fifth gear.

I took it apart again, inserted a thicker wire in the idle feed restriction (0.024", reducing the flow area by 1/3th) and at the same time, I also installed #66 jets (instead of the stock #68), a 3.5" power valve and the stiffest (black) spring in the secondary canister (it had the next to lightest yellow one, which I assume is what it came with). Not very scientific perhaps to make so many changes at the same time, but I had grown tired of taking the carb apart all the time.

Anyway, idle AFR remained at ~13, light cruise (on the transfer circuit) increased the AFR to ~13, cruise (on the main jets) to 14.5-15 and WOT to ~13. It smelled much less and drove smoothly without much hesitation. There's still some under some conditions, so a little more tuning of the acceleration circuit required I guess, but overall it drives well. At 6000 RPM, manifold vacuum crept up to maybe 1" Hg (hard to see exactly when trying to look at the tach, the vacuum gauge and of course the road at the same time...), so I guess the stiff secondary spring didn't make the carb very restrictive. The light cruise AFR didn't increase as much as the flow area reduction suggested but I guess that's due to the unchanged secondary idle circuit. Maybe I'll give it one more go and fix that too.

[Drew Pojedinec]

The original 3259 had a .031 ifr, I consider this a touch too small. Early 3259-1 had a .033 ifr which is perfect.
Later 3259-1 and reproduction ones (as well as 4118) have a .040 which is massive. Reduce to .033

I do this regularly and am lauded as some carb genius...  (I am not, it's physics).
.033 ifr and .070 idle air bleed is appropriate for 90% of all cars with a 1 5/16, 1 3/8 venturi, 1 11/16 throttle bore carb.
Very rarely does an engine require being outside of this range.

[mygt350]

Misplaced my notes or they are in my filing system, somewhere.
Can anyone please tell me, again, what metering block numbers are correct for a 3259-1 Holley from a 66 GT350?
Thanks

[Helmantel]

Mine are now at the equivalent of .0323 but still a little rich, at least for my engine. On an actual GT350 it may be different.

I wonder why they made those idle feed restrictors so large? I understand that they already did that during the 60's?
Do you know if they increased the secondary idle feed as well?

[Drew Pojedinec]

No, secondary ifr was .031 on all of them.

.033 shouldn't be overly rich, or it should be within range to correct with mixture screws.
The only reason I can see running larger would be due to a radical camshaft. As the camshaft duration or intake plenum becomes larger, more fuel is required.

Example:
If I take a cobrajet carb with it's typical .076 idle air bleed, and .029 ifr and put it on my truck engine (20in vac at idle, stockish cam, small edelbrock intake), it will run flawlessly as is with mixture screws out 1 turn.
If I take the same carb and put it on my Galaxie (250@.050 cam and massive Tunnelwedge intake), it will barely run with the mixture screws 2.5 turns out.  I would have to alter the idle feed.  I could drill ifr to .035, or could reduce idle air bleed and increase ifr to something like .067/.033

Fairly drastic changes.

[TA Coupe]

I may have missed it but was fuel pressure ever checked? Or does it make much of a difference on these carburetors. I have only messed around with 4160 carburetors and it does make a big difference.

       Roy

[Helmantel]

I didn't check it, but it's a regular 289 fuel pump. I did rev it up to max with the sight plugs off to see if fuel level rose abnormally but it stayed were it was so I called it good.

I had a look at Holley's chart for secondary springs which listed the start of opening and fully open engine speeds for a 350 and a 402 with a 3310 (750 cfm) carburetor. The different values scaled almost perfectly with the difference in displacement between the two, so I recalculated them for a 289, also taking into account that secondaries are a little larger and thus flow a little more. The results are in the chart. For the black spring it actually said that it didn't fully open so I had to make a guess here for the "fully open RPM".

As I wrote yesterday, manifold vacuum was just about to creep up (an inch Hg or so) at 6000 RPM with the black spring installed. The theoretical air consumption of a 289 at 6000 RPM is ~500 cfm, which matches the chart almost perfectly. Maybe dumb luck, because I made several assumptions, but still fun to see.

[Drew Pojedinec]

My way of tuning secondary spring is to use a quick change pot.
Find the bog, and scale to heavier until desired results occur.
Once found reinstall original housing with appropriate spring.

The charts are ok ish. Like many such charts it would be hard to take all factors in account....
Especially that there is a bleed hole from the primary signal hole to the secondary.
This is not the same size on all carbs. On old holley spec sheets the bleed hole was noted.