Best Carb for the job????

This has probably been gone over before, but I figure heck, we all love to talk about our cars and since we can’t get out into the parking lots with the whole pandemic thing I’d like to open the floor up to opinions... that’s right fellas, not necessarily facts but opinions on what he best carb for the job would be?

My car: 1972 351 CJ (4v) 4 speed

Stock engine, except:

Headman long tubes, edelbrock dual plane intake (I believe it’s square, but I guess if push comes to shove I’d need to confirm) MSD IGNITION drop in distributor, and a Holley 670 street avenger carb. 

The carb has been set up and chassis dyno tuned for the car. That said it seems to bog down a bit from idle to first gear, meaning if I get on it to hard it sort of sputters. Car is right there otherwise. I’ve been told it’s almost too small of a carb so it was rejetted(carbs are vudu to me boys)so I does seem to smell a little rich.

What are you guys running? What’s worth the investment? And what gives some room to grow should I choose to came it or a future rebuild. 

Cheers!

This has probably been gone over before, but I figure heck, we all love to talk about our cars and since we can’t get out into the parking lots with the whole pandemic thing I’d like to open the floor up to opinions... that’s right fellas, not necessarily facts but opinions on what he best carb for the job would be?

My car: 1972 351 CJ (4v) 4 speed

Stock engine, except:

Headman long tubes, edelbrock dual plane intake (I believe it’s square, but I guess if push comes to shove I’d need to confirm) MSD IGNITION drop in distributor, and a Holley 670 street avenger carb. 

The carb has been set up and chassis dyno tuned for the car. That said it seems to bog down a bit from idle to first gear, meaning if I get on it to hard it sort of sputters. Car is right there otherwise. I’ve been told it’s almost too small of a carb so it was rejetted(carbs are vudu to me boys)so I does seem to smell a little rich.

What are you guys running? What’s worth the investment? And what gives some room to grow should I choose to came it or a future rebuild. 

Cheers!

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Hi Ricard,

This may or may not help, but apart from the MSD, intake and headers, your set up isn't that different to mine, 351C 4 V 4 speed M code. Yours is a Q code. I actually had one of those the same, but sold it back in 91, stupid, stupid!!

Here's what you need to check imo, The Holley 670 S/A isn't the best, but what I have also. It may depend on you cam to a large extent and I'm no expert at all on that subject. Other can offer more info on that. If I were to buy another carb, I'd be looking at the Quick Fuel HR735 or Summit Racing have a good one under their name brand.

The easiest way to describe what you might need to do, is to outline what I have on my basically stock motor. 

Timing, initial is set at 14 degrees, no vacuum. there is 20 deg. on the crank, so total mechanical is 34 deg. @ 3000 rpm all in Check your damper and pointer are correct.

Carb. 65 main jets, 67 secondary's. Power valve 6.5. idle screws set 1.5 turns out. I did change the squirter for larger, but I don't recall what number off-hand.

Now, here's where there was a mod made. I had much the same thing and running rich at idle. I took the car to a local tune-up shop and their guy who builds race car engines, drilled a 3/32" hole in each of the primary throttle plates then set the secondary's correctly. A lot of times, we mistakenly open up the primary's to get it to idle.

The transfer slots must be to spec at .020" or look "square".

My engine produces 17-18 "Hg.

Hope that's a start. After I did the timing and carb the bogg was gone... most of the time anyway. Sometimes it seems to be weather related as well, cooler the better.

Geoff makes some excellent points here. I will add in the 670 is likely on the small side for that set up. a 735 or 750 should be more it the sweet spot but again it will need some level of tuning to get the most out of it. I'm running a Quick Fuel 750 with mechanical secondaries. I can post the mods (tuning) done to mine tonight when I get home as I have my notes in the shop. Also, that is a vacuum secondary carb you are running. Since you are running a 4 speed and also want to leave room for growth should you decided to go with a more aggressive cam down the road I would highly recommend a mechanical secondary carb.

Geoff knows his stuff.  ::thumb::

I have a similar set-up as well:

• Edelbrock Performer intake
  
• Hooker Competition long tube headers
  
• Duraspark ignition
  
• Accel Super Coil
  

I'm running an Edelbrock 1406 with zero issues.

Thanks guys, for the input. It’s definitely cool out today, 6degrees Celsius so it runs real nice once it warms up, I’m definitely thinking it’s starving for a bigger carb because when it was on chassis dyno, the race shop owner tuning it said the same and really “knows his stuff” . Probably should have just said order what you think works but we both thought we could get it close without opening the wallet to much more.

That said no one knows better then the owners of these cars since you all have seen it and can probably completely understand this problem from the few words I write!

Thanks!

Now, here's where there was a mod made. I had much the same thing and running rich at idle. I took the car to a local tune-up shop and their guy who builds race car engines, drilled a 3/32" hole in each of the primary throttle plates then set the secondary's correctly. A lot of times, we mistakenly open up the primary's to get it to idle.

I'd still love to see where exactly on the plates those holes are drilled. : )

Geoff knows his stuff.  ::thumb::

I have a similar set-up as well:

• Edelbrock Performer intake
  
• Hooker Competition long tube headers
  
• Duraspark ignition
  
• Accel Super Coil
  

I'm running an Edelbrock 1406 with zero issues.

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Eric, I got you fooled!! lollerz

Thanks for the compliment.

Now, here's where there was a mod made. I had much the same thing and running rich at idle. I took the car to a local tune-up shop and their guy who builds race car engines, drilled a 3/32" hole in each of the primary throttle plates then set the secondary's correctly. A lot of times, we mistakenly open up the primary's to get it to idle.

I'd still love to see where exactly on the plates those holes are drilled. : )

The reply pain did not separate as usual.

The holes drilled are in the center of the primary plate and in the middle between shaft and front edge. If that doesn't make sense, I'll have to go and pull off the air cleaner and...….. Never mind I'll take a picture and post it, I'm really not sure myself now.

Stay tuned.

Yeah, I can't see all the way to the primary plates with the choke plate and the squirters in the way. So the holes are about centered both ways front of the shaft. It's not that critical.

Another great thing to consider is a better intake manifold. The Edelbrock performer intake is pretty much like stock, but not bad. If you go to a Blue Thunder or an Air Gap, then you will really wake that motor up. Makes a big difference in the rpm range, but that’s when you go with a bigger cam.

I have a a Quick Fuel 735 on my 72 Q Code and I really like it.

I am giving these carbs a try here is 1 for a higher Hp motor https://fstcarb.com/products/41750b-1/

Something a little calmer https://fstcarb.com/product-category/carburetors/rt-x/

Something more stock https://fstcarb.com/product-category/carburetors/rt/page/2/

Their made in Detroit and have some nice features.

If you want room to grow I suggest you look at something in the 700-780 CFM range. Pay for adjustability, ie. changeable idle channel restrictor,s idle air bleeds, and high speed air bleeds. The best bang for the buck in this regard are Quick Fuel and the Summit carb (it is a third generation Autolite 4100 carb). No two engine combinations are the same so different carb tuning will be required. You can drill and tap these holes to make the size changes needed BUT, it is not easy to do without hosing up the carb (requires modifying the choke housing, small bits, a drill press, operated by hand, a steady hand with the taps, an improvised fixture, and an assortment of bleeds and restrictors). The SA series is notorious for being fat at idle and cruise. I had to restrict the idle channel and open the idle air bleeds to make it function closer to optimal. It wasn't worth the effort in my, after the fact, opinion.  I think QF may offer the Ford style float bowls(fuel enters on driver's side) from and transfers to the secondary side from the passenger's side primary bowl. Let us know what you decide on. Chuck

One more thing to check if you have a flat spot is the pump arm adjustment. My carb had a loose pump arm and it caused a weird little flat spot when I would first accelerate. It's free to check!!

I ran a Quick Fuel 680 HR with vacuum secondaries on the 71 Mach 1 i did last year. Runs great on a mainly stock motor.

I had a 71' Mach 1 with 351C that was to Boss spec........Boss clone.

Holley 750 DP, Offenhauser intake, strip cam, Hooker Super Comp's headers, 3:91 Drag Pack.

It was an absolute beast.....but....I could only hold a tune on that Holley for 6 months, and seasons in PA change quickly.

Currently have a Edelbrock 1406 600CFM on my 302 in 73" vert, and its old nasty and never lost  performance after sitting a few months.

Call Edelbrock and ask there engineer's for the proper CFM carb for your engine and mods.

I dont think I'll ever run another carb but Edelbrock.........just my opinion. ::thumb::

Again thanks for all the advise. I’ve always run Holley carbs and quite frankly I’ve always had adjustment issues... but I guess I just keep going back to the same mistress again and again hoping for a different outcome!

The quick fuel does sound interesting , as well as the summit carb, I’ll have to look into pricing. I never thought of the pump arm. I will give that a look and see what’s what there.

I did change the fuel filter and found some bits of what I am pretty sure is the old float from a sending unit... I’m going to guess from 10+ years ago? I was thinking that could have been starving the motor because it was maybe settling at idle and being pushed up on acceleration, but it seems to be continuing so, at least the problem has been mitigated.

If the particles are from a sending unit float filter, maybe it's time for a fuel system replacement of tank and sending unit, steel lines and rubber pieces. You have probably read past posts on rust and dirt in old tank and lines, so if your system is original, chances are you are into some of this and crap is getting through.

As for checking the acceleration pump arm and you probably already know this, but you should be able to get a .015" feeler gauge to go under the arm with the throttle arm at wide open. This is to ensure there is still some give in the diaphragm. If not it's too tight.

Did you look at some of the Edelbrock YouTube video's that were posted? Again, I'm not  a fan, but there is some interesting stuff there especially on fuel pressure, which may or may not be the cause of a lot of problems with other carb brands.

Nothing wrong with the 670 Holley, just the lame marketing that they're "drop on and go" out of the box. No carb is ever that ready to go, I don't care who makes it.

IMO, the best bang for the buck going is the Summit carb, it's a re-issue of the old Holley 4010 series from the 80's. I have a 4010 600 double pumper on the 302 in my 71 Mach and love it. Once I fixed my f-up with the float level, it has run perfectly ever since.

For a 4 speed 351CJ, I'd lean towards a 750DP.

https://www.summitracing.com/search/product-line/summit-racing-m2008-series-carburetors/part-type/carburetors/cfm-range/700-799-cfm?N=cfm-range%3A700-799-cfm&SortBy=BestKeywordMatch&SortOrder=Ascending

Nothing wrong with the  670 Holley, just the lame marketing that they're "drop on and go" out of the box. No carb is ever that ready to go, I don't care who makes it.

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 Agreed, but it was close apart from being fat at idle. The 3/32" holes drilled in the primary plates fixed that issue. Not everyone will agree with that either.

Nothing wrong with the  670 Holley, just the lame marketing that they're "drop on and go" out of the box. No carb is ever that ready to go, I don't care who makes it.

Click to expand...

 Agreed, but it was close apart from being fat at idle. The 3/32" holes drilled in the primary plates fixed that issue. Not everyone will agree with that either.

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Yeah, the guy doing my machine work gets all bent out of shape when he sees drilled throttle plates.