250 build tunning and stuff

6

69stang_250

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Happy New Years and all that good stuff!

So I moved back to Louisiana and got my car out today for some tunning. Figured it would be better to put all of this on one thread instead of a bunch of different ones.

Here is what I saw today.

Checked timing: set it at 34* at 3000 rpm initially and left alone. What I saw today is 14* at 1000 +-100 rpm. Checked advance from 2000-3000 and it's all in before 2500 rpm. Once I hook up the vacuum advance the rpm jumps 400 +-100. Does this sound right?
Mind you the vac advance is hooked to the manifold vacuum. If I idle the engine down to 1100 with the vacuum advance hooked up the rpm drops to about 800 or so when I stop. I'm guessing the manifold vacuum drops and can't keep the rpms up? How should I set the idle speed? If I'm stuck at a 1500 or so idle speed I'll live with it, but just want to make sure I'm doing this right. If you guys think the timing is off let me know. I know this needs to be dialed in before I get the carb done.

Now to fuel. At idle I've got it staying 13.7-14.9. Sound good? Once I hit the gas it drops to about 11.5-12.5. I know I need to work that one out. Out on the road wot in first drops to 11 second drops to 11.5 and creeps up to 13.5 and in third I start leaning out to 13 and creeps into 15s before I shift. Once I'm cruising I stay at 14-15 but if I punch it in fourth I'll lean out to 17. Bigger jets? Or power valve?
I have a 10.5 in there now an 66 primary an 64 secondary jets installed right now.
Also, should I put a fuel regulator in my plumbing? I know they aren't very expensive I just wonder what size I need to get for the Holley? 1-4 psi? Or 4-9 psi?
One thing I noticed today is that I can't tell if the secondary is full or empty when I look through the the sight glass. It started raining on me so I didn't pull the carb to check, but I may be doing that once I get our garage cleaned up so I can fit the car in.

Even with all that I can say that it has a ton more power than before. Timed 0-60 at 5.4. I don't think that is bad at all for a 250, 3.97 first, open 3.00 in the back, and some wet roads lol


Hope you boys and girls are having a great New Year's Eve and be safe!
 
For starts it looks like you need to move the vacuum advance line from the manifold port to the timed spark fitting in the choke side of the primary metering block.

I believe the rest was covered for you by Bill.
viewtopic.php?p=585585#p585585
After you get your jetting worked out then you can try WOT in forth to find out what the power valve circuit is doing.
 
Quote:
"No, set the idle so it is smooth at the highest A/F it will stand at a decent quality. Get the highest rpm & then lean it down till you get a 25 RPM drop & see what readings you have & is the idle quality still decent.
Next go for the cruise-main jet calibration at 55-75 mph. Change main jets to get 14.3-14.7 ratio.
Now block the secondary throttle from opening at WOT. Take it up to 4000 RPM's only WOT on the primarys & go for 12.5-13.1 A/F.
If the A/F is in that range you are ok, if not a professional will have to install screw in restrictions under the power valve known as the PVRC.
If you luck out & the WOT is in those specs, then un-block the secondaries & go for a WOT to redline RPM & still go for the same #'s as before. If too rich install smaller jets in the secondarys.
The transition just driving around the neighborhood @ 15-25 mph should be at least over 13-1. If its in the 10-12.9 area the idle restriction needs to be decreased from say .035" to .031" area, another area for a professional.
I do this work all the time & it is time consuming.
I will not get into metering block mods at this time.Bill"

Ok so I have been working on the idle and this is what I have.

Got the air fuel ratio between 13.2-14.8 running at 1050rpm. Sounds good, but once I hit the throttle it has a hesitation and then it throws my air fuel ratio off by going a little leaner. I know I need to just get it in a good range and go with it, but I don't feel good about leaving the idle and it jumping from 13s-14s to 15s and 16s.

Should I just get it in a good range and don't sweat it? And then fine tune as I work on the Cruise, accelerator circuit, and wot?
Also I read in an artical on Holley vacuum secondary tunning that opening the secondary's 1 1/2 turns on the screw helps with long duration cams. Should I try this to maybe help out with the idle?
 
Ok so here is what I have after getting the idle set up as perfect as I think I will get it.

Idle: I have gotten the AF ratio jumping from 13.5-14.6. I noticed that I could not see any fuel in the secondary so I tried adjusting with no luck. Took the screw completely off and I guess I screwed the needle and seat in too far. Took the carb off and fixed that along with checking the secondary blades. Those are completely closed off. After all that I noticed that my idle air screws on the secondary has a mohair affect on the AF ratio. If I have the mains out 1 1/2 turns it runs 16-17 with the secondaries completely closed. Opening them 1 turn puts me at 10.5-12. I've gotten it evened out, but the mains are opened more than the secondaries. Is that a problem?

Cruise: at 50 it is in the 13.7-15 range. Good for me.

Wot. When I punch it, it drops to 10 and creeps up to 13.5. When I'm in second and third and hit 3000 it strats pulling hard and leans down to 16 for a second and then goes to about 10-11. no hesitation when you are rolling and floor it, but a small. One when you are at a dead stop.
 
This is where Bill said to lock out the secondary side from opening and concentrate on getting just the primary side correct.
Then unlock the secondary side and see what it contributes.
It looks like the secondary side could be rich now that you fixed the fuel level.

You didn't mention if you moved the vacuum advance line to the timed spark fitting in the choke side of the primary metering block?
If you did what is the idle rpm and manifold vacuum

The power valve rating should be about half the idle manifold vacuum
 
not to be too fussy
but it would B nice for 'assisters" if U had
the build in ur signature (down below, ya know?) -
just B a quick way for some 1 to scan data for the back
knowledge when offering ideas, not hafta go over all the seperate
threads. And it's a great build, U can B proud of what you've assembled!
( I myself keep 4gettin, I think u have the alu head? )
Best o da New Year
 
so I blocked off the secondaries initially and got the idle smooth as could be with just using the mains and then tried to even the mains and secondaries out. At idle all 4 corners should turned out the same amount correct? Right now the mains are open more. I have not hooked up a vacuum gauge because I've been using an air fuel gauge to tune it. I have read and have been told that I just need to tune from the air fuel ratio. Do I still need to hook up the vacuum gauge? If so I'll be going to pick one up today.

I did hook the advance to the ported vacuum. It works helps at stop lights keeping the car from stalling out. After getting the Air fuel ratio in the high 13 -14 range the idle smoothed out at 1070-1100 rpm. It idles great right there. Engine doesn't bounce all over the place and it's got the advertised "choppy" idle from the cam.

Chad- I'll be adding that signature today.
 
Ahhh, kouwell, that helps.
From what I've heard the vacuum gague would B 1st (& primary), and the a/f 2nd and more 'finer tuning'…
Nice carb, I honor U for ur wrk, choice and skill.
 
also added - I C ur new address - ain't that where Steve Stills lived 4awhile (Covington)?
I got family in the area - Franklinton (& lands end Lafitte, Barataria Bay)...
U round Franklington when they had an ostrige farm? ~ 60 y/o uncle caretook the 'farmer' & 'crop' while back!
:shock:
:LOL:
 
My thoughts are that carbs a bit large for your aplication. 450 ish would be a better size. You should hook up a vacuum testing gauge to see if the vacuum is holding close to 0 at high speeds floored were it is going lean.

https://www.quickfueltechnology.com/car ... er-series/

Have been thinking of this one myself. Which in my case might be too small but with a small log ported head and a circle track cam my 250 will go over 7000 RPM easy


At any rate if your running 66 in the front possibly need 70s in the rear as a start. Power valve rate is based on vacuum readings. You should check primary idle transfer slot orientation to the throttle blade.
 
Ok so I got a vacuum gauge and I've got the idle dialed in great now. 1050 rpm 13.4-14.3 AFR at 9 on vacuum. When the electric fans kick on it drops to 950rpm 13.9-15 AFR and bounces between 7 and 9 on vacuum. There is no hesitation or anything when I hit the throttle and it's seems to like the settings when the fans kick on.

I will be going for a drive a little later to see how it does cruising a WOT, but I am going to head to the parts store and see if they have the power valve I need. It has a 10.5 installed right now and I need a 4.5 I'm assuming, does that sound right?

Turbo- I know it's a bit on the large side, but it is tuning out ok, just taking me some time and learning. The jetting is 65 primaries and 63 secondaries right now. I am not sure how much of the transfer slot is exposed at idle, but I had to turn the idle screw 2 complete turns out in order to get it to stay at idle once warmed up. That is where I left it and tuned from there.
 
If you have turned the idle speed screw out 2 turns (to slow idle) the idle transfer slot is most likely almost if not completely covered up. Sto see it one has to remove the carb. About .030 to .035 of the slot should be visible below the primary throttle blades. Thats about how its set from the factory. If possible to kep it in proper position closing the rear throttle blades should be used to slow the idle. In opposite instances open it to speed it up.
In most cases the carb has to be removed to change rear throttle blade position. I do mods replacing the secondary throttle stop with a alen head screw and a spring so it can be adjusted while the carb is on and running.
Not sure if that mod could be done on the aluminum head 4 bbl intake. I have a head and intake on a bench HOPEFULLY A LOOSE CARB i moded to check clearances.

tHERE ARE OTHER MODS TO POSITION primary throttle blades properly but I SAVE THEM AS A LAST RESORT.
 
o0OPp-
double post
sorry
 
69stang_250":2qfk1c3s said:
Ok so I got a vacuum gauge and I've got the idle dialed in great now. 1050 rpm 13.4-14.3 AFR at 9 on vacuum. When the electric fans kick on it drops to 950rpm 13.9-15 AFR and bounces between 7 and 9 on vacuum. There is no hesitation or anything when I hit the throttle and it's seems to like the settings when the fans kick on.

I will be going for a drive a little later to see how it does cruising a WOT, but I am going to head to the parts store and see if they have the power valve I need. It has a 10.5 installed right now and I need a 4.5 I'm assuming, does that sound right?
Click to expand...
Yep it sounds right
If the vacuum is right around the power valve rating, the PV will be opening and closing making the A/F ratio move up and down.
Once you get the right PV installed it won't richen the mixture until you load the engine going down the road.
Then you can change the main jets to get the A/F right (If it needs to be done).
 
Before picking up a power valve do some highway cruising and read the vacuum gauge as sometimes idle vacuum and cruse vacuum fight each other.
 
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