Ok, one more question on the Holley jetting.

[yellow rose]

very carefully
I drilled and tapped a piece of 1" aluminum bar stock for 6-, 8- and 10-32.
Setscrew threaded into the bar, bar located on tabletop drill press, then drill very gently (fingertip pressure).
I'd like to have a mini lathe but I don't.

Nothing wrong with that. Same way I do it except I have a lathe here. When I help someone else I use a drill press or a hand drill to hold the fixture and drill it.

I assume you have a pin vise? If so, I usually start .004-.006 smaller drill than I want and and then finish with the drill I want. It’s easier to keep the hole sizes where you want them. I always pin drill everything when I’m done to make sure it’s where it should be.

 

[DrCharles]

The more I think about it, I don't see how the AFR could ever be constant or leaning out (before the mains come in) with a big cam. Idle AFR set with the needle screws wherever it likes, as long as there's enough range, ok.

But as Mattax said, AFR richens as the vacuum rises off idle from the 7-8" idle vac, sucking harder on the t-slot and the t-slot provides more fuel from the bottom of the slot (and less air bleed at the top of the slot too).

Seems like it will be a compromise at best. If I make the AFR right with the full t-slot feeding, won't it be way too lean just off-idle, which will cause a lean stumble?

Edit: yes, I have a pin vise although I haven't tried your exact method yet.

 

[TrailBeast]

Today I made the IFR smaller (maybe). Didn't make much noticeable difference!
I don't have the precision equipment to drill .033 instead of .034 with sufficient accuracy. Will increase the IAB slightly. If still too rich, then I'm going to make the TSR smaller.

Trailbeast, any progress with yours?

You can put a strand of wire in the IFR and bend it over. The gasket will hold in there. When you get it right you can calculate the area and drill a permanent IFR.

The more I think about it, I don't see how the AFR could ever be constant or leaning out (before the mains come in) with a big cam. Idle AFR set with the needle screws wherever it likes, as long as there's enough range, ok.

But as Mattax said, AFR richens as the vacuum rises off idle from the 7-8" idle vac, sucking harder on the t-slot and the t-slot provides more fuel from the bottom of the slot (and less air bleed at the top of the slot too).

Seems like it will be a compromise at best. If I make the AFR right with the full t-slot feeding, won't it be way too lean just off-idle, which will cause a lean stumble?

Edit: yes, I have a pin vise although I haven't tried your exact method yet.

Ok here's what I found.
I used a paper clip bent in half and inserted it into the small hole where the home made jet would go.
Two strands of the paper clip didn't make any difference at all.
Three strands barely made any difference in the T slot feed. (maybe .2 of an AFR number)
Four strands came a little closer but I had a lean flat spot just off the idle stop.
(Felt just like the pump shot not working)

For now I went back to stock and have a rich spot (9.5-10 to one) just as the throttle comes off the stop and right where my throttle is most of the time around town under normal driving.
Next will be the power valve change as @yellow rose suggested, but I can't find my dang vacuum gauge.
I'm going to pick up another one today so I can find the one I have.
The one thing I don't understand is how a power valve that opens sooner as YR suggested is going to have any affect on this rich spot off idle.

So in conclusion in my case limiting the T slot and idle feed didn't even come close to fixing the rich spot.
Now I have to think it all through as to why.
It seems my rich spot has nothing to do with the T slot, but it must still be well before the main jets come in.
WTH?

I did swap out my 75 main jets for 68's and now 45-60 or so cruise is good.

 

[TrailBeast]

Ok I took it out for a drive and paid much more attention to what and when with a vacuum gauge on it.
I have 15in of vacuum at idle with a 14-15 AFR, and 10 at the light throttle cruise where it shows in the 10:1 range.

#72 jets in the mains 6.5 power valve, and at 1,200 rpm's it goes rich and stays about there until I get into it to about 1/2 throttle then it shows 12.5-13 AFR as long as I have that throttle opening.
If I back off on the throttle any it starts going rich again until I hit the idle stop and then it comes back to around 14-15 again.

WOT shows 10's also even though I jetted all the way down to #66 jets in the secondaries.

No matter what speed or what gear I am in it shows 10's in the 1,200 rpm range.
And as I said it shows 10's at WOT even with #66 jets in the secondaries.

I'm going to make absolutely sure the secondaries are opening here in a bit with a paper clip on the vacuum diaphragm rod.

 

[Mattax]

and 10 at the light throttle cruise

Wow Greg. My gut reaction is WTH?
IMO At light throttle cruising the engine should be pulling a heck of a lot harder than that.
I'd expect a minimum or 14"Hg and as high as 18"Hg depending on rpm, speed and whether a slight up downhill.

 

[TrailBeast]

Wow Greg. My gut reaction is WTH?
IMO At light throttle cruising the engine should be pulling a heck of a lot harder than that.
I'd expect a minimum or 14"Hg and as high as 18"Hg depending on rpm, speed and whether a slight up downhill.

Um, can I ship my *** over there so you can kick me in it?
I put the paper clip on the secondaries vac can rod to make sure they open and as soon as I started the car the AFR was around 18 at idle WTH?
As I pulled away from my driveway for the test drive the light throttle was so close in the AFR it was ridiculous.

Made a WOT run for about 3 seconds and when I checked the paper clip it hadn't moved. (they are not opening)
Looks like I'm on to something, so I'm going to pull the vac unit and see what's up.
It looks/acts like the secondaries were getting involved in the off idle somehow.
I'll pull the vac unit here in a few and take a look.

That explains why the #66 secondary jets didn't change much at WOT.

 

[Mattax]

Made a WOT run for about 3 seconds and when I checked the paper clip it hadn't moved. (they are not opening)

That's could be correct depending on the spring and the actual airflow.
Ever seen the logs I made on a chassis dyno with different secondary springs?

 

[Mattax]

In fact my suggestion is get the primary side to work correctly. So disconnect the secondaries, that way you won't be thinking about them. Or put a black spring in if that makes you feel better.

 

[TrailBeast]

That's could be correct depending on the spring and the actual airflow.
Ever seen the logs I made on a chassis dyno with different secondary springs?

Have not seen your logs, but I'd like to.
I found one issue and fix it though.
This secondary vac can has the black two piece cap so the spring can be changed.
The little top piece that comes off to remove the spring sits on an oring to seal the can so vacuum can pull the diaphragm.
That top piece was not sitting all the way down on it's oring (There was a slight air gap)
I took it off the carb and tested it with vacuum and the actuator rod didn't move.
A couple of passes with a flat file on the mating surfaces to get the powder coating off allowed it to sit down on the oring and it opens now and holds vacuum.
Also put a new seal where it meets the carb body

The Wife is taking a nap now and the car is about 8 feet from the bedroom window, so no testing until later.

FYI, I do have a 214/224 cam in the motor, but I didn't think that was big enough to matter on the vacuum.
I can lock out the secondaries (just read your last post while I was typing)
It has a silver spring in it currently.

One thing I can't get my head around is when I put the paper clip on the secondary rod to test the opening of them the primary side looked good on the AFR.
That off idle rich spot was gone. WTH?

Thank you for your input on this.
I appreciate it.

 

[Mattax]

Now I'm just guessing. Maybe the secondary was cracking or flopping open enough to expose the secondary transfer slot?

Of course I can't find any of the screen shots I made of three springs.
I'll have to open up the dyno files and do over.
Until then, here's a couple of overlaying wide open throttle with and without the secondaries.

Main thing to notice.
Engine accelerates pretty darn well on just two barrels of the '750'.

The carb here has a downleg secondaries and annular primaries. I suppose the thinking was the annular booster restrict flow so using downlegs in the secondaries would make up for it. Nice thought but messes up fuel distribution and never would recommend it. Anyway as you can see the primary AFR is pretty flat and the secondary AFR is rich, lean, richer and drifts lean.
Disconnecting the secondary demonstrated that problem was entirely in the secondary side.

Datalogger shows that more clearly.

Bottom scale is time in seconds.
Blue is vacuum. According to the MAP, vacuum came up to 3.5 "Hg at 5700 rpm using just the primary barrels.

Suppose I should mention a little about the engine:
340 with hughes cam 223/230 at 50.

 

[TrailBeast]

Now I'm just guessing. Maybe the secondary was cracking or flopping open enough to expose the secondary transfer slot?

Of course I can't find any of the screen shots I made of three springs.
I'll have to open up the dyno files and do over.
Until then, here's a couple of overlaying wide open throttle with and without the secondaries.

Main thing to notice.
Engine accelerates pretty darn well on just two barrels of the '750'.
View attachment 1715497858

The carb here has a downleg secondaries and annular primaries. I suppose the thinking was the annular booster restrict flow so using downlegs in the secondaries would make up for it. Nice thought but messes up fuel distribution and never would recommend it. Anyway as you can see the primary AFR is pretty flat and the secondary AFR is rich, lean, richer and drifts lean.
Disconnecting the secondary demonstrated that problem was entirely in the secondary side.

Datalogger shows that more clearly.
View attachment 1715497860
Bottom scale is time in seconds.
Blue is vacuum. According to the MAP, vacuum came up to 3.5 "Hg at 5700 rpm using just the primary barrels.

Suppose I should mention a little about the engine:
340 with hughes cam 223/230 at 50.

I wondered about the secondaries possibly opening for some reason, and the only thing I could come up with was possibly just vacuum.
That seems like it shouldn't happen though because of the spring.

Now get this.
After I got the top of the vac can down on the Oring everything came real close into line and the secondaries work now.
Remember the last I said was 72 primary jets.
All the way down to 66's in the secondaries with no change.
10 or so on the AFR at 1,200 rpm.

Now the AFR shows everything right about where it would be expected in relation to what the carb has in it right now.
Now it shows 13.5-14 at idle. ( I did have to richen it up again after the O ring sealed)
about 12 where that rich spot was at 1,200 rpm.
14-15 once into the primary jets.
And 16-17 when the secondaries come in at WOT. (makes sense with 66 jets)

Looks like all I have to do now is get 72-74's or so in the secondaries so it's around 12-12.5 at WOT and trim the idle a little leaner and that should be completely acceptable.
A bit leaner on the idle should all but remove that rich off idle spot.

Who the heck would have thought that Oring not sealed to the vac can would cause all this whacked out crap?
Secondaries not opening sure, but everything whacked through the whole carb?
This is one of the things that could make guys throw a carb in the trash.

The car is snappy, strong and is back running really nice again, just faster than it ever has been.
The Edelbrock ran great on it, but it wasn't this great.

Thank you for all your effort on this, and I really do appreciate your consultation.

Now remember.
A non sealing oring that seals the quick change vac spring cover can screw your carb up good.
I know I won't forget it.