Need help with Holley carburetor tune.

[338Raptor]

I don’t know what had been done to the carb before I got it.  I know the motor ran way worse than it does now. It had 80/87 jets in it and 35 nozzles. It ran 10 to 1 AFR at WOT. It also stumbled really bad at initial throttle, that’s why I increased the nozzle size to 40’s. It doesn’t stumble now but that’s probably making up for the fact the transition slots aren’t working.
When trying to get more mid throttle fuel I drilled the PVCR’s .002” over what I thought was standard.  But now I’m unsure if I really know what this carb is without a List number. So I may have drilled them larger than I intended. If necessary I can epoxy and redrill smaller.

I’ll check the base gasket and if that doesn’t fix it I’ll be in the market for a new carburetor.

[fryedaddy]

i bought a 950 a few years ago,used.when i put it on my car and cranked it up it sounded awesome,but when i took off down the road it fell flat on its ass.he had 70s up front and 72s in the secondary with no power valves either place. i put 80s up front with a power valve and 88s in the secondarys with the power valve blocked.it screamed after that.

[My427stang]

I don’t know what had been done to the carb before I got it.  I know the motor ran way worse than it does now. It had 80/87 jets in it and 35 nozzles. It ran 10 to 1 AFR at WOT. It also stumbled really bad at initial throttle, that’s why I increased the nozzle size to 40’s. It doesn’t stumble now but that’s probably making up for the fact the transition slots aren’t working.
When trying to get more mid throttle fuel I drilled the PVCR’s .002” over what I thought was standard.  But now I’m unsure if I really know what this carb is without a List number. So I may have drilled them larger than I intended. If necessary I can epoxy and redrill smaller.

I’ll check the base gasket and if that doesn’t fix it I’ll be in the market for a new carburetor.

I think that's a good call.  Sometimes carburetors get so much "super tuning" done to them you need to basically replace most of it to get back to the starting point.

Hopefully it was just a throttle body to base gasket blocking the transition circuit but if it isn't, I'd go with something nice.  Considering the engine underneath it, it's worth a good carb

[338Raptor]

I found more info on the carb.
It’s 860 CFM built by Pro Systems. It is built on a Holley HP format with some billet parts.  They sent me all the specs so I can go back to a starting point after I install new gaskets.  Hope to have the gaskets installed and road tested later today. 

[My427stang]

I found more info on the carb.
It’s 860 CFM built by Pro Systems. It is built on a Holley HP format with some billet parts.  They sent me all the specs so I can go back to a starting point after I install new gaskets.  Hope to have the gaskets installed and road tested later today.

Did you find the incorrect gasket in there?

[338Raptor]

No. The gasket was correct, all the holes lined up and all the transfer slots look good with no obstruction. I disassembled air bleeds and everything and blew it out with carb cleaner.  No problems found. I’ll test drive it tomorrow but I seriously doubt anything will change.  I put all the jets, pump cams, etc back to the original tune from the carb shop.  I also verified all the orifice sizes and they all checked out.

[My427stang]

Nice work, hopefully it comes together. 

How different was the original setup compared to yours, other than the accel pumps and shooters?

[338Raptor]

Problem still exists.

The original tune was the same tune I started with.
I triple checked every port/slot/orifice and made damn sure everything was sealing and there where no cracks or leaks. I’m 99.99% confident everything is assembled correctly. 

This is the result (same as before)
1. Idle is good at 1000 rpm and 11” vacuum at 13.7 to 1. Four corner idle mixture adjustment  (1 +1/8 full turns out) and all 4 throttle plates are just barely exposing the transfer slots. This is where it has the most vacuum)
2. When I smash the throttle from idle it goes lean 20-1 for a split second. Like the squirters aren’t providing enough fuel to compensate for the blast of air. (Running black and orange cams)
3. WOT is 10.5 to 1.  Still too rich. (Primaries and maybe secondaries too large)
4. Cruising is 12 to 1. Still too rich. (Primaries too large)
5. Roll into the throttle from cruising speed and it goes super lean 17-20 to 1. When this happens it snaps and crackles for 1-2 seconds then goes rich when I hit WOT.
6. I’ve tried 4.0, 5.0, and 6.5 Standard flow power valves. Same result. 

It’s like the power valve isn’t richening it up under load.  PV vacuum port is clear and flows freely.  All PV ports are clear and PVRC is .0600 like the carb manufacturer recommended.

Carb manufacturer recommending sending to them for rebuild but that will be a 2 week turn around.  I would like to avoid that.

[My427stang]

Problem still exists.

The original tune was the same tune I started with.
I triple checked every port/slot/orifice and made damn sure everything was sealing and there where no cracks or leaks. I’m 99.99% confident everything is assembled correctly. 

This is the result (same as before)
1. Idle is good at 1000 rpm and 11” vacuum at 13.7 to 1. Four corner idle mixture adjustment  (1 +1/8 full turns out) and all 4 throttle plates are just barely exposing the transfer slots. This is where it has the most vacuum)
2. When I smash the throttle from idle it goes lean 20-1 for a split second. Like the squirters aren’t providing enough fuel to compensate for the blast of air. (Running black and orange cams)
3. WOT is 10.5 to 1.  Still too rich. (Primaries and maybe secondaries too large)
4. Cruising is 12 to 1. Still too rich. (Primaries too large)
5. Roll into the throttle from cruising speed and it goes super lean 17-20 to 1. When this happens it snaps and crackles for 1-2 seconds then goes rich when I hit WOT.
6. I’ve tried 4.0, 5.0, and 6.5 Standard flow power valves. Same result. 

It’s like the power valve isn’t richening it up under load.  PV vacuum port is clear and flows freely.  All PV ports are clear and PVRC is .0600 like the carb manufacturer recommended.

Carb manufacturer recommending sending to them for rebuild but that will be a 2 week turn around.  I would like to avoid that.

OK, so first, don't deduce anything, right now, let's use your post as gathering data.  With all love and kindness, you seem to provide data with your decision already, let's just look at the data.

1 - Idle - You idle OK, but on a 4 corner idle circuit, generally you don't go 1 1/8 out like a primary only.  That starts to tell me that maybe you could use a little bigger IFR, that would bring the screws in and more importantly, feed the idle and transition with more fuel.  However, before we determine that, what is your IFR size?

2 - Throttle smash - you have a delay where it goes lean.  How do you adjust your accelerator pump?  Also, is it an umbrella or steel ball check valve?

3 - Ignore WOT for now, that will be the easy one

4 - What changes did the PV make, is 6.5 less lean than 4.5?, and when you are cruising, what is the vacuum? 

5 - What are your current HSAB sizes?

6 - What if any markings are there on your throttle blades?

7 - What is the full setup of the carb now, jets, accel pump shooters, cams, PV value 

Shoot those answers back, but I will ask you one more.  If you grab the boosters, are they loose?

Something is happening here, it's either a lack of transition fuel or a booster that isn't starting when it should.  Don't make any changes yet let's keep picking.

One last repeat, do you have any other known carb even if too small, that you can throw on there just to verify that it is the carb?  Heck I have a known good 3310 if you need one to try, cheapo, not pretty, but could loan it if you promise not to go inside of it

[338Raptor]

I have an 850DP I’ll put on it for a test.

I’ll clean it up and put new gaskets in it first. It’s been sitting for 20 years.

[Cyclone03]

An easy test but not 100% all the time back all the mixture screws out 1/2 turn more and drive,you goal is to roll in the throttle not stab it. See if it pulls smother.

[338Raptor]

I’ll try that but I think the problem is after the transition.  After the throttle plates have already uncovered the slots and the idle ports are not a factor. 
But I’ll try anything. 

[Cyclone03]

Work the throttle slow, you need to try to separate the circuits ,slamming the throttle open will not get the carb tuned you need to work it from bottom to top. Idle-WOT.

By richening the idle mixture you should see a change,you would be surprised how long a Holley is running in the transition circuit.

[338Raptor]

Opened up the idle screws 1/2 turn and no difference other than 12 to 1 AFR at idle instead of high 13’s. It still has a super lean spot under light load (1/3 to 1/2 throttle). Everywhere else it’s still too rich.  It acts like the Power Valve circuit isn’t working at all. I’ll put on my other carb and see how that works.

[70tp]

I once fought a 3310 Holley with a lean spot in it like that and I eventually found that I had a gasket that blocked one of the fuel passages.  Acted just like what you are seeing.    Another one had something inside the metering block that had some crud or something in it.  Used some aluminum cleaning acid in that circuit to “boil it out”