250 build tunning and stuff

If it hesitates off the line at WOT it would point to the primary side being a little lean with a 63 jet.
Get that worked out first as it will richen when both the primary and secondary are open.
Leave the secondary alone for now.

Once you get the primary back in shape then you can focus on the secondary if it still needs it.
Nice Work!
 
You should go up 2 jet sizes at a time in the front bbls. Still wondering what power valve you have in there.
Sometimes I unhook the secondary at the C clip to keep the secondarys from opening just to get it running close to correct on the primary jetting. You might have too much accelerator pump did you change the sqirter size.

How to check idle jetting start engine let it warm up to normal temp. Starting at idle slowly depress the gas pedal so the accelerator pump dosent squirt. Watch tach needle it should slowly rise if there is a flat spot or the needle drops fuel curve is off. You can try riching up the idle screws or lean out see if it improves. This is done while not driving the car. idle circuit in most cases transfers around 2000 to 2500 RPM to the main circuit. If tach drops between the 200 2500 RPM point it probably going lean at tip in of the main jets. If the tach jumps at that point it might be too rich of a main jet.

Big thing is only make one change at a time. Change 2 or more things at a time it becomes difficult to figure which change helped or hurt
 
Ok so after everything we have done here is where it's at.

Idles great between 12.8-13.7 around 1100 rpm.
Cruises around 12.5 until you go up a hill and then it will lean out all depending on the %.
WOT from a dead stop has a hiccup off the line and rises to a 10.5 and then emediatly leans out to 17 until the secondaries kick in, at about 2500-3000 rpm and then richens to about 13.2.

Just normal driving I stay in the 12.5-14.3 range.

This is after all of the adjustments that we have done.

Currently
primaries: are 63s w/6.5 power valve, curb idle screw is a 1/2 turn more than the initial setting, 31 squirter w/ orange cam in # 2 position.

Secondaries: throttle plates are closed, 68 jets and the purple spring.

One thing to note is the smooth transition between the two is getting out of wack now.
I will be putting the yellow spring back in.

With all of that the primaries are running lean at WOT. Is that a squirter issue? Or jets?
I'm trying to connect these with wide open throttle, as that is the only time it goes lean or if you are below 1900 rpm in 4th or 5th and punch the gas.

I have a set of 65 jets I can try in the primaries. I'll mess with that and let y'all know how it does from there.
 
turbo2256b":1jffrl45 said:
How to check idle jetting start engine let it warm up to normal temp. Starting at idle slowly depress the gas pedal so the accelerator pump dosent squirt. Watch tach needle it should slowly rise if there is a flat spot or the needle drops fuel curve is off. You can try riching up the idle feed screws or lean out see if it improves. This is done while not driving the car. idle circuit in most cases transfers around 2000 to 2500 RPM to the main circuit. If tach drops between the 2000/2500 RPM point it probably going lean at tip in of the main jets. If the tach jumps at that point it might be too rich of a main jet.

Big thing is only make one change at a time. Change 2 or more things at a time it becomes difficult to figure which change helped or hurt


The above should be the next step. It will also determine weather the car is cruising on the idle circuit or main circuit. So also whats your highway steady Cruz speed / RPM on a flat highway and A/F/vacuum
 
69stang_250":15cu8nrw said:
Ok so after everything we have done here is where it's at.
Cruises around 12.5 until you go up a hill and then it will lean out all depending on the %.
WOT from a dead stop has a hiccup off the line and rises to a 10.5 and then emediatly leans out to 17 until the secondaries kick in, at about 2500-3000 rpm and then richens to about 13.2.

I have a set of 65 jets I can try in the primaries. I'll mess with that and let y'all know how it does from there.

Looks like the primary main jets need to be larger.
With a 17 A/F you may end up close to a primary 68 main jet again to get it back down in the 13s at WOT.

As previously suggested, don't change more than one thing at a time
When you swapped the primary and secondary jets around, that is "Changing two things at once". It can cause confusion and makes more work.
 
pmuller9":gco5zdvz said:
69stang_250":gco5zdvz said:
Ok so after everything we have done here is where it's at.
Cruises around 12.5 until you go up a hill and then it will lean out all depending on the %.
WOT from a dead stop has a hiccup off the line and rises to a 10.5 and then emediatly leans out to 17 until the secondaries kick in, at about 2500-3000 rpm and then richens to about 13.2.

I have a set of 65 jets I can try in the primaries. I'll mess with that and let y'all know how it does from there.

Looks like the primary main jets need to be larger.
With a 17 A/F you may end up close to a primary 68 main jet again to get it back down in the 13s at WOT.

As previously suggested, don't change more than one thing at a time
When you swapped the primary and secondary jets around, that is "Changing two things at once". It can cause confusion and makes more work.

I believe the OP swaped front and rear jets 68s in the rear he put in front and 63s in the back were the fronts from the factory. Since the carb is large for the application pressure drops through metering orfaces are out of wack.
 
From what I have read 65 front were factory and 68s rear would go back to this configuration before doing the above test I mentioned.

Most of whai I have read about this carb is increasing the jetting used on 350s and more cu in engines. Best to do a bit of a restart here and be a bit more mithotical.
 
Sorry I've been a little busy with getting things around the house done and have not had time to really mess with the car.

But, I ordered another set of 68 jets just in case and will be running the 65 jets first to see if that fixes the problem.

I will only be messing with the primaries until the lean issue is addressed and then will adjust the secondaries as needed.

I do have a question regarding the CFM for you guys.

A 600 vac secondary seems to be a nice carb choice for the 6s and I have never read anything negative about them being ran. Everything I have read about the 670 street avenger makes it sound like it is a 600 vac secondary with different boosters and a bunch of adjustability upgrades. My question is, if they are basically the same and only flow more cfm due to the booster design, does that still creat "lazy" air flow with the 670? Or is it the Venturi size that will ultimately dictate the air speed?

I'm not sure if that is asked correctly.
 
69stang_250":et6ob2t5 said:
Sorry I've been a little busy with getting things around the house done and have not had time to really mess with the car.

But, I ordered another set of 68 jets just in case and will be running the 65 jets first to see if that fixes the problem.

I will only be messing with the primaries until the lean issue is addressed and then will adjust the secondaries as needed.

I do have a question regarding the CFM for you guys.

A 600 vac secondary seems to be a nice carb choice for the 6s and I have never read anything negative about them being ran. Everything I have read about the 670 street avenger makes it sound like it is a 600 vac secondary with different boosters and a bunch of adjustability upgrades. My question is, if they are basically the same and only flow more cfm due to the booster design, does that still creat "lazy" air flow with the 670? Or is it the Venturi size that will ultimately dictate the air speed?

I'm not sure if that is asked correctly.
Even a 600 is a bit oversize for a 250 (even at 7K rpm) though some of the 600 cfm carbs work well enough. A 500cfm carb might be a better fit...
 
Rich - it's the alu head... don't that flow near theroitical optimal?
Still 500 cfm's best?
 
chad":gveed0jy said:
Rich - it's the alu head... don't that flow near theroitical optimal?
Still 500 cfm's best?
unless you are running well over 7Krpm, and have ported that AL head, yes... perhaps even a 450... I used 85% for VE, which I think is generous for an as cast AL head...
 
69stang_250":zjbq97jt said:
A 600 vac secondary seems to be a nice carb choice for the 6s and I have never read anything negative about them being ran. Everything I have read about the 670 street avenger makes it sound like it is a 600 vac secondary with different boosters and a bunch of adjustability upgrades. My question is, if they are basically the same and only flow more cfm due to the booster design, does that still creat "lazy" air flow with the 670? Or is it the Venturi size that will ultimately dictate the air speed?
For Holley and most other carbs the throttle plate butterfly size goes from 1 [sup]9/16[/sup] to 1 [sup]11/16[/sup] when going from a 600 to 650.
The venture size stays at 1 [sup]1/4[/sup] primary and 1 [sup]5/16[/sup] secondary

I would look at the new Summit M2008 Series 500 and 600 cfm carbs. They have annular boosters.
 
Thank you for all the info.
 
With some tuning the 670 can be made to work but most likely not quite as well as a more proper sized carb. Things like a really stiff spring in the secondary so it comes in much later to possible not opening all the way and jetting can be a start.
 
This discussion on VE and cfm is entirely based on US V8 logic, not any practical work the US guys have had with a 250 large runner in line six with even spaced ports.

Go to any Aussie 200/250 X-flow or 202 Holden forum, and they won't even have these low cfm carb discussions and aspirations, because low cfm carbs just don't work with I-6/L-6 engines.

One of the greatest engine tuners in Australia is Kevin Bartlett, a Gold Star F5000 driver, Ford 351 campainger and GM 350 expert.

In 1990, He said this:-

"250 Falcon Cross flow with Alloy head, go to 4150/4160 Holley 4-bbl 600 cfm vac sec, and set it up with a huge flat spot when going into the secondary barrels".


The reason for the big carbs with the open runner I-6'S?


On an I6 like the Classic Inlnes or 2V 250, or Cross flow 200/250 with 2 or 4bbl carb, a 2-bbl 500 cfm or 650 cfm, or 4-bbl 600 cfm Vac sec or 650 double pumper will provide the fuel an I6 requires.


This is due to flow efficency problems with an I6.

Essentialy one zone of fuel supply THEN has to distibute out to six cylinders via a 22 " long intake with over 2 liers or 121 cubic inches of ruuner volume.

That needs CFM to fill quickly. If you come down on cfm, it starts to revert to 10:1 to 15:1 air fuel ratio swings cylinder to cylinder. This morbid fixation with reducting CFM does not apply to an I6 because there needs to be inlet runner volume to avoid reversion and fuel stand off, and reducing carb venturi size then produces excessive air speed which creates extra issues with calibration. 4 cylinder guys have found 4-bbl carbs run better than 2-bbl carbs on big cam engines with Holley carbs. The same with I6's.

Most 250 to 365 hp 4.1's get better results with a 650 cfm Double Pumper Holley 4-bbl.

The difference is that any good Windsor GT40 or Cleveland US V8 or Pinto 2.0 EAO OHC or Fox/Ranger Lima 2.3 OHC are IMHO the most higly developed engines on earth, with cylinder to cylinder flow efficencies of up to 80% from cylinder to cylinder. That means air fuel ratio swings of less than 1 air fuel ratio between any cylinder. Along with that, the intake manifold and carb is only a 10 to maybee 15% flow drop from a bare intake flow CFM. That means if you have 165 cfm at 28 "H20 from one cylinder, the intake and carb flow for an 85% VE carb selection on a 2.0/2.3 I4 or 5.0/5.8 V8 the flow drop will be down to 144 cfm. So you can run a NASCAR on a 390 cfm Mech Sec Holley and get 700 hp or more with perfect cylinder to cylinder air fuel, or a 2-bbl 500 cfm carb on a 2.3 Lima OHC and get 265 hp net with perfect cylinder to cylinder air fuel.


Try a 500 cfm Holley 2-bbl on an I6, and it looses a lot of power over even a 390 cfm carb. Pump up the cfm, and power figures go up exponentially.

Its just an I6 thing, that was found out by Repco engineers in the late 60's, and that is why those old Antipodean racers always dialed up huge 4-bbl intakes or even bigger port on port triple carb systems. Going down to little 4-bbls just gave them less hp and no drivablity improvements

There is no stale, dead air in an even fire in line six with a 2 liters of intake runner volume. Its just a nice enviromnet to sit a big a$$ 4-bbl, and then dial up the air fuel until it gives a good drivablity.

4-bbl in line sixes beat V8's out of the hole shoot, and the bigger the cfm, the better.

The idelised cubic inches times peak rpm divided by 3456 formula is a great tool for V8's, not for I6's.

A final word.

In Australia, the Commodore Challenge 4.2 liter V8's used to make 290 net flywheel hp do 155 mph, and 290 hp with just one 465 cfm Holley 4-bbl, but thats a nice intake manifold of one of the best flow efficency V8's. The factory carb on 81 to 84 4.2 liter V8's was a 725 cfm Quadrajet 4-bbl, and it gave 16.7 second quarter miles with just a 155 net hp engine. When you dongraded the carb to 465, you could get even more power. It could go up to about 334 dyno hp, or 377 Engine Analyser hp with just a 465 or 600 cfm Holey 4-bbl


But an I6 is not a 4.2 or 5 or 6 liter v8, or a 2.0-2.3 liter I4

An I6 needs about 40% more cfm than a V8 to even see the same hp readings.

An ex Ford engineer

See "Restoring the American Dream:130 mph for the Masses" by Csaba Csere

built a1981 Mercury Capri 4.2 4-bb hot rod, the lamest Ford for its time V8 ever, and needed 600 cfm to make a 132 mph road burner. Doing anything less than 600 cfm of a 4-bbl I-6 will suck the life out of it...

http://vb.foureyedpride.com/showthread. ... res-needed

The Aussies found in 1 and a half hours an other 90 hp on there little league 4.2 pip squeek engines. They then wanted to go to a 500 cfm Holley 4-bbl, down from a 600 cfm 4-bbl, to get more power. But that's V8's. And its typical of any dyno check. Why do you think 5.0 2-bbl 1982 Mustang GT's ran so darn hard on a 369 cfm 2-bbl 1.21 Motocraft 2150 carb?

V8 logic is just that, for V8's.

Not i6's. tOTALLY dIFFERNT hEAD...


Johnny%2BSlash.jpg



See this

http://s76.photobucket.com/user/Litre8/ ... 3.jpg.html

I6's don't like reduced cfm, because of air fuel ratio and intake mnifold geometery.
 
Hey guys sorry I haven't been on much.

So I finally got my fuel regulator mounted in the car and put 68s in the mains. It cruises in the high 13s now with no issue cruising around town is still good and I have no flat spots.
Now I need to work on the accelerator circuit due to a lean spot off the line at wot.

also today while I was messing with the car, I found a vacuum leak. I did not know there was a port that went into the choke and when I removed mine I did not plug it, but I did today. I will be doing some more running on the carb, however I also ordered one of the summit 600 carbs. I have read nothing but good things about these carbs and have read and seen people say on YouTube that it feels and runs better than a Holley 600.
So we shall see next week.

After I get this part down it's changing the rear end gearing for me. I know there is a lot of totenial to tap into with that engine.
 
Install the 50cc accerator pump & use the brown cam just like the 4412-500 2bbl. Use .029"-.031" nozzles. Use a 7.5 power valve.Treat the primary like a 2bbl & after the WOT hesitation from a stop is gone then go after the secondary's.
 
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