69 390 Advice

Keecho · Mar 16, 2016

Hello
Just looking for some advice on top end stuff.
I have a 69 scode 390 with ram air option and im having some issues with previous owners build.
It has the boat anchor intake, stock heads and exhaust manifolds, aftermarket billit distributer and street avenger 770 carb. Im having idling issues to start with, it idles 2500 at the lowest no air leaks and i dont know much about that carb or jets and maybe a faulty distributer ( not sure)

I just want to take all that crap off and toss it.
Should i just buy mid range eldelbrock intake/heads/ new carb/ new distributer/ and get some decent exhaust manifolds?

Oh the only part im not sure on and main reason i came here is i have to keep the ram air on. I dont care about functionality so much but i need it to fit and seal. Im guessing i can always space the carb up or down an inch or so but i have to be within that.
Thanks in advance
Jack

LILCBRA · Mar 16, 2016

Sounds like your carb is too big. I had the same exact issue years ago with a V6 Mustang II. I got it with no carb, but had a V8 2 bbl carb laying around. I used it and it had a really high idle until I was able to replace it with the proper sized V6 carb. I'd start with the carb, maybe try a 650 or something like that to see if it responds the way you want before getting in too deep replacing the whole top end.

Keecho · Mar 16, 2016

Thanks, never thought of that, your the first person to suggest it, alot of people suggested the 770. But yea i played with the advance, timing, carb settings, idle, checked for leaks all over, choke etc, never been able to bring the idle down. Your the first person to suggest carb size. Alot of people said 770 is fine so never crossed my mind. I really dont need any of the race stuff, car has plenty of power for me but i was thinking the og parts are so rare and hard to find its actually cheaper to upgrade and buy new so thats why i was asking.

LILCBRA · Mar 16, 2016

No problem! I hope there isn't something else hiding somewhere that you didn't know about, but this sounds exactly like what I experienced years ago. If you were close, I'd let you try my 650 double pump just to see if it works the way you wanted since it's off of my car for the time being. If you know of someone who has a carb to try, I think I'd try borrowing one first so I didn't shell out the money for a new carb right away....

Keecho · Mar 16, 2016

What kind of carb do you guys reccomend? Like what is the model of that 650 double pump? When i look up holley 650 double pump they range anywhere between 250 to 1500 $ whats the diffrence? I just want something solid and maybe easy to tune/ rebuild in the future.
Thanks again

LILCBRA · Mar 16, 2016

I'd say probably go with a vacuum secondary Holley. You won't need the most expensive one on the market, so you can probably go with one of the lower priced carbs. There will be some tuning involved no matter what, so if you don't know how to tune a Holley, you may be better off finding a reputable speed/dyno tuner and enlist their help. You may be able to get a good start by calling someone like Summit Racing's tech support. They may be able to give you a solid starting point as far as what carb to try, what jet sizes, spring sizes for the vac. secondary actuator, etc.

Upon entering the engine, the Summit website found 2 matches for a carb. This is the cheaper of the 2, the other being about $100 more.
http://www.summitracing.com/parts/hly-0-80457s/overview/make/ford

Keecho · Mar 18, 2016

I found a new street avenger 670 on amazon for $420 i dont mind the extra 100 dollars. Is it a good carb? What you guys think? Is the 670 still to big or ok?

LILCBRA · Mar 18, 2016

I am no expert by any means, but I ran some numbers through Summit's carb estimator (http://www.summitracing.com/expertadviceandnews/calcsandtools/cfm-calculator). If you plan on revving your 390 to about 7000 rpm and your volumetric efficiency is around 85%, then a 670 cfm should do fine and is listed as the "street" carb. If you drop the rpms down to about 6000, then it estimates the "street" carb at around 575 cfm and the "race" carb around 740 cfm. So I guess it then boils down to how your car is built and how you plan on driving it. Personally, I think the 600 would probably be best if your engine is basically stock because it falls between the "street" and "race" categories of this calculator. I don't know if you can spin the 390 to 7k rpm or not, I have no experience with them. But I'll bet the 600 would suit you just fine if you're built pretty close to stock. It would probably idle right where it needs to and perform well in WOT situations. Anyway, play with that calculator a little and I'll bet you can get a feel for what size you may want to run. I tend to go somewhere between their "street" and "race" recommendations and depending on the build I would go closer to one than the other. Stock closer to the "street" value and obviously "race" more toward a highly modified engine.

Oh, and to give you an idea between the calculator and "real world application", the 770 you had on your car initially is listed as the "street" carb if you were looking to spin it around 8000 rpm.....

LILCBRA · Apr 11, 2016

I was just thinking of this thread and I know the chances are slim now since it's been almost 3 weeks since your last log in, but how did you fare? Did you find a carb to try and did it help/get you where you wanted to be?

Keecho · Apr 14, 2016

I sent the 770 back to amazon and bought a 670 in return. Carb is sitting on my desk and i havnt got a chance to try it out. I will post back results hopefully early next week. I been fiddling with my boat lately trying to get it ready for summer and havnt spent much time on the stang. If i can get it to idle correctly im gonna redo my clutch. If it doesnt idle and have same issues i will probably just go with a whole new edelbrock top end setup, heads, intake exaust along with this new carb.

LILCBRA · Apr 14, 2016

Best of luck!! I hope it works out, sounds like it'd save you a boatload of money (no pun intended) if it does!!

7991LXnSHO · Apr 24, 2016

If you spin a normal street 390 to 7000 rpm, you will probably no longer need a carburetor. A big bag of oil dry, a dustpan and a broom, then a tow truck will be of more use. Hot Rod (I think) tried to hop up one, and spun it too fast. I predict valve float much past 5500 rpm. So that might be a better number to use in your calculations.
But keep in mind a vac secondary carb should not open the secondaries any farther than you need. So if the 750 square bore only needs 600 CFM, you are covered. Too big of a double pumper will possibly bog when floored.

barnett468 · May 2, 2016

Keecho said:
I sent the 770 back to amazon and bought a 670 in return. Carb is sitting on my desk and i havnt got a chance to try it out. I will post back results hopefully early next week. I been fiddling with my boat lately trying to get it ready for summer and havnt spent much time on the stang. If i can get it to idle correctly im gonna redo my clutch. If it doesnt idle and have same issues i will probably just go with a whole new edelbrock top end setup, heads, intake exaust along with this new carb.

the size of the carb is NOT the cause of your high idle . you could put a 950 on it and have it idle at 700 pm.

the 670 is too small for a performance app but will certainly work decent.

if it is a vacuum secondary carb, for optimal performance you need to buy additional secondary springs and try lighter ones until it starts to bog when flooring it.

the avenger carbs are crap . buy a re holley or quick fuel.

remove and plug the distributor vacuum advance unit for now until you get it running right then plug it into ported vacuum.
.

7991LXnSHO · May 2, 2016

Street Avenger carbs are sold by Holley. It seems they have been buying up many companies that are copies of basic Holley designs. The good news is Holley has been putting the better features on more of their models. One of those is the quick change secondary spring housing. Another is the visible fuel bowls, rather than those easy to drop plugs and washers or weak, fire hazard clear fuel bowl plugs.

I have always had all my lines hooked up right for tuning. If you have that high of an idle, I wonder if you have a massive vacuum leak, bent throttle blades or something keeping the throttle open a bit. That could be the idle set screw or the linkage. Also check your distributor advance timing.

69 390 Advice

Keecho

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LILCBRA

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Keecho

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I wish I didn't have all of these balls in the air

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LILCBRA

I wish I didn't have all of these balls in the air

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I wish I didn't have all of these balls in the air

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I wish I didn't have all of these balls in the air

Keecho

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I wish I didn't have all of these balls in the air

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