is my carb to big???

[67coupestang]

hey guys, quick question for ya... I have a 67 coupe with a 351W a tremec, standard dual exhaust with shorties, and 2.7x rear gears. the performance is a bit lack luster for what i'd expect... I wondering if my carb is too big for my current setup... its a 78 351W out of a t-bird, with stock cam and heads, and when i say stock cam i mean this thing idles smooth with no lope. I have a edlebroc performer intake with a carter 750 manual choke. it just seems like when i put my foot in to it, it just sounds like it bogs... case in point last summer when it was still an automatic, i was leaving work one day and some buddies were out there and well ya know.. I put my foot in to it about 1/4 and it rolled them over better than it does if i put it to the floor... it also has duraspark ignition, if maybe thats not hot enough? let me know what you guys think...

 

[D.Hearne]

Yep, your motor would do better with a 600-650. If your carb is a mechanical secondary it would also do better with a 750 vacuum secondary carb.

 

[7DMACH1]

Way to big!!!!!! A 600 cfm should be plenty!!! RAY

 

[allcarfan]

change cam, change gears, take advantage of your carb

 

[67GTA-FB429]

Too big. I have a 750 on a built 429 and it is plenty except at high RPMs. You can also change the jets. You can make it smaller, but not bigger.

 

[SL 1993 R]

have to agree with everybody else,, way too big...

 

[D.Hearne]

You cannot make a carb smaller by changing jets. No Way, No How, Ain't gonna happen. When are you people gonna learn. This is Carbs 101, not EFI. You could get a Nascar restrictor plate and run restrictor rings under it, but you ain't gonna jet it smaller. Or you could by a $700 BG Demon carb with changeable throat inserts to make it smaller, but you ain't gonna jet a carb down in size!!!

 

[Blown4.6]

Too big....unless you operate it at 8500 rpm...just kidding. Yea, it's too big. Like everyone else, I'd use 600 cfm. I'd go 500-600 depending how you drive it. 650 is fine too, just a little less signal at low rpm.

 

[67GTA-FB429]

Hearn: Sorry about that, smaller was a bad word choice, maybe better explained through the word "leaner".

 

[HistoricMustang]

It would support a Holley 750. I know several guys running 750 Holley's on 289/302's. Got a buddy that runs an 850 on his 347. When you run a Carter or Edelbrock it is a different ballgame. You got to go down on the CFM's. I know it does not make sense but neither does the fact that we always see the same side of the moon even though it rotates just like us here on earth.

HistoricMustang
www.historicmustang.com

 

[67coupestang]

so what if i change heads and cam?? is it still too big??? and if so... anyone running a big block that would trade me for like a 650??

 

[D.Hearne]

Hearn: Sorry about that, smaller was a bad word choice, maybe better explained through the word "leaner".

You're forgiven I just went off base, this is the 4th or 5th time here lately that I've heard that same thing, "jet it smaller" I blew a fuse. But seriously, there are lots of guys out there that wern't even born when the last carbed Fords rolled off the line, and haven't a clue as to how they work. Then there's others that give the wrong advice as to how to make that 850 carb on a small block "smaller" so it'll work better.Instead of getting a carb that's closer to being the right carb the first time.

 

[D.Hearne]

so what if i change heads and cam?? is it still too big??? and if so... anyone running a big block that would trade me for like a 650??

Yes, a better set of heads and/or a bigger cam will make that 750 a better choice for your motor.

 

[GaPonyFarm]

Even with aftermarkets heads and a very agressive cam, that carb is too big. You should be able to trade with somebody who has a 600 or 650, and doesn't know better.

 

[67coupestang]

Still having thoughts about this... and trying to clarify something... is the bigger CFM causing to low an intake velocity? Is my engine running to rich or too lean? I pulled the plugs after running for a while and they are clean and white... they dont look burnt, no carbon, they look new. also in 5th gear at low rpms if i mash the gas it sputters and backfires when i open the secondaries. I lessened the accel pump stroke and it took out some of this.

 

[mustang70]

You're not going to get much of a response in 5th gear with gears that tall. And yes, the large carb is affecting the signal to your venturis which affects your throttle response.

If you really want to trade someone, let me know. I'm looking to upgrade to a bigger carb for my motor.

 

[67GTCOUPE]

Even with aftermarkets heads and a very agressive cam, that carb is too big. You should be able to trade with somebody who has a 600 or 650, and doesn't know better.

I disagree.

First off the carb is a quasy vac secondary......so it should be ok with your motor......but it is a Carter/Edelbrock, so it is a mystery how to fix it or set it up.

Personally: I really suggest that you do yourself a HUGE favor and get the Edelbrock performer RPM cam and intake, and heads if you can. Then get yourself a Holley 750 vacuum carb.......like a provac from these guys: www.quickfueltechnology.com

That will put your 351 up to 400+hp and believe me......it will impress you.

 

[jikelly]

I've got a carter 750 carb on my 351w with tremec tranny, a somewhat agressive cam and super high flow heads. Well I kinda have some of the same issues that your having but I need to tune my carb before I do anything drastic like trade for a smaller one or move to a holley design.