Time For New Carb?

[73pony]

Ah ok. My only concern with mechanical secondaries is that I believe I have the vacuum line from the distributor to the vacuum secondary header. I have never used a mechanical secondary carburetor so I'm unsure how I'd install it on my current setup. Mechanical sounds way more beneficial though

There are still manifold and ported vacuum connection on a mechanical secondary carb.

 

[Stanglover]

Ah ok. My only concern with mechanical secondaries is that I believe I have the vacuum line from the distributor to the vacuum secondary header. I have never used a mechanical secondary carburetor so I'm unsure how I'd install it on my current setup. Mechanical sounds way more beneficial though

 The Summit website state that the 750 Brawler series can be ordered with VACUUM secondary's, so that is what I'd go for myself. Do your research and buy the best bang for the buck.

Let us know what you decide.

 

[Stanglover]

Do you know if the Slayer Series 750CFM is also a double pumper like the Brawler? It has the dual fuel inlets it says on summit's site

No it's not a double pumper, but has dual feeds and float chambers. It does have 2 metering blocks though.

 

[Stanglover]

Ah ok. My only concern with mechanical secondaries is that I believe I have the vacuum line from the distributor to the vacuum secondary header. I have never used a mechanical secondary carburetor so I'm unsure how I'd install it on my current setup. Mechanical sounds way more beneficial though

 The vacuum line from the distributor does not operate the secondary's. It's for timing only. The vacuum secondary's are operated through the carb itself when there is a load on the engine. They do NOT work when the car is not being driven. There are different schools of thought, but IMHO, the vacuum line should go to the Timed Port on the carb, located on the primary metering block, not manifold vacuum as you don't need vacuum at idle and if you have 17" of vacuum, your timing will be way off.

 

[icejawa]

Oh then I might be getting mechanical secondary version since it has the double pump. Of course I was on board earlier for the vacuum secondary carb but I really love that double pump concept.

 

[Don C]

An article about which to choose:

http://www.hotrod.com/articles/vacuum-or-mechanical-secondary-carburetor/

And a video from Summit Racing:

 

[Stanglover]

Oh then I might be getting mechanical secondary version since it has the double pump. Of course I was on board earlier for the vacuum secondary carb but I really love that double pump concept.

It looks like you CAN get the DP with vacuum secondary's. Check Summit's website as I have zero idea how to link it here. Give me a wrench, fine, but a computer, well it may as well be on another planet!!

Look up BR-67213 750 Brawler. The last sentence states they have mechanical or vacuum secondary's. I'd call Summit to make sure, but looking at the Holley video Don put up, it you have a 4 speed manual, it seems like either option will work, but the mechanical might be better. I learn every day!!

 

[TheRktmn]

For ease of installation, no need for a lot of tuning out of the box, easy maintenance, and light hit on the wallet, I'd go with the Summit. Plus, it is very well rated.

https://www.summitracing.com/parts/sum-m08750vs/overview/

+1 for the M2008 series. I ran Autolites, Holleys and Edelbrocks for years. Each had something I liked - the M2008 has it all.

 

[73pony]

Oh then I might be getting mechanical secondary version since it has the double pump. Of course I was on board earlier for the vacuum secondary carb but I really love that double pump concept.

It looks like you CAN get the DP with vacuum secondary's. Check Summit's website as I have zero idea how to link it here. Give me a wrench, fine, but a computer, well it may as well be on another planet!!

Look up BR-67213 750 Brawler. The last sentence states they have mechanical or vacuum secondary's. I'd call Summit to make sure, but looking at the Holley video Don put up, it you have a 4 speed manual, it seems like either option will work, but the mechanical might be better. I learn every day!!

I think that last sentence is poorly worded. The brawler series carb is available in either mechanical DP configuration or Vac secondary configuration, but not both at the same time. You wouldn't want that extra shot of fuel on a vacuum secondary carb as it uses the vacuum to open the secondaries, thus if enough vacuum exists to open the secondaries there is enough vacuum to pull fuel. The idea of the DP is that extra shot of fuel when you mash the throttle and the linkage opens the secondaries immediately (via linkage) giving it the necessary fuel until vacuum catches up to pull it.

 

[TommyK]

All the adjustability of the newer carbs is great if you know how to tune a carb or are willing to invest the time ( in my case years because I am not to bright) to learn how to tune one.

For a novice I think the Summit carb is a great suggestion.

 

[Stanglover]

Oh then I might be getting mechanical secondary version since it has the double pump. Of course I was on board earlier for the vacuum secondary carb but I really love that double pump concept.

It looks like you CAN get the DP with vacuum secondary's. Check Summit's website as I have zero idea how to link it here. Give me a wrench, fine, but a computer, well it may as well be on another planet!!

Look up BR-67213 750 Brawler. The last sentence states they have mechanical or vacuum secondary's. I'd call Summit to make sure, but looking at the Holley video Don put up, it you have a 4 speed manual, it seems like either option will work, but the mechanical might be better. I learn every day!!

I think that last sentence is poorly worded. The brawler series carb is available in either mechanical DP configuration or Vac secondary configuration, but not both at the same time. You wouldn't want that extra shot of fuel on a vacuum secondary carb as it uses the vacuum to open the secondaries, thus if enough vacuum exists to open the secondaries there is enough vacuum to pull fuel. The idea of the DP is that extra shot of fuel when you mash the throttle and the linkage opens the secondaries immediately (via linkage) giving it the necessary fuel until vacuum catches up to pull it.

 Jason, I see your point. In that case it is ambiguous. Perhaps Summit need to rewrite that to be clear to ********* like me!!

 

[Stanglover]

Just for s**t's and giggles, I emailed Summit Racing's tech dept. to ask for clarification on the Brawler situation as well as to get a better idea of the differences between the various models QF offer. I also asked for more info on the Summit M2008, like where is it made? Still awaiting their reply.

 I did this not only for Icejawa, but for my information too. While my current Holley 670 is fairly good now, (I did need to have it slightly modified by drilling a 3/32" diam. hole in the leading side of the primary plates as it was starving for air at idle without opening up the transfer slots, too rich. This was done by a qualified tuner by the way). I feel I could get more out of the engine and bumping up to a good 750 might be the way I need to go.

I'll post their reply when I get it.

Geoff.

 

[Hemikiller]

My vote goes for a 750-ish double pump carb as well. I've successfully run 800DP Holleys on all of my 351C-4V engines with no issues. It's pretty obvious to your foot where the secondary comes in.

IMO, a new carb is a huge waste of $$ if you have the ability to rebuild one yourself. Literally the only thing that wears out on a carb is the baseplate and new ones are available for $100 or less. I've bought double pumpers at swap meets for $100 or less.

If you want to save some bucks, you can get a refurb 4779 750DP off eBay direct from Holley for $350. If you want electric choke, get the kit for it.

https://www.ebay.com/itm/Holley-0-4779C-750CFM-Double-Pumper-Factory-Refurbished-4bbl/281835138756?epid=169503708&hash=item419eaeeec4:g:xQkAAOxyLN9ShAyr&vxp=mtr

As far as tuning, I've had good luck with a larger primary acc. pump nozzle and a more aggressive ramp on the pump cam. That gets rid of any off idle lean bog .

 

[ITMike5.0]

I'll be going with a new carb for my 351C - 4v as well... Can you use any of these after market carbs with the original intake or do you have to replace that as well?

 

[Hemikiller]

I'll be going with a new carb for my 351C - 4v as well...  Can you use any of these after market carbs with the original intake or do you have to replace that as well?

They will bolt right onto the stock square bore iron intake, but you need to use a spacer so that the throttle plates clear the intake. IIRC, you'll need around a 1/2" thick at a minimum.

 

[Stanglover]

I'll be going with a new carb for my 351C - 4v as well...  Can you use any of these after market carbs with the original intake or do you have to replace that as well?

They will bolt right onto the stock square bore iron intake, but you need to use a spacer so that the throttle plates clear the intake. IIRC, you'll need around a 1/2" thick at a minimum.

............ and make sure it's an insulated one especially if your manifold has not had the heat cross-over passages blocked off. Fel-Pro make a base gasket with a metal insert between the paper layers for the Ford 4V manifolds that you'll need under a spacer if the heat is still getting to the carb base. There was another thread here recently where this was discussed. Sorry I don't have that part number at hand.

Refer to post #29 351 4V carburetor in Engine and drive train.

 

[Ron Tanzi]

Using a Holley with Vacuum secondary quick change kit as Stanglover suggested is my choice. As far as selecting CFM rating (650 should be enough) it is about your engines volumetric efficiency. I am not a big fan of the Edelbrock/carter AFB carbs on our engines (fine for Mopars). The throttle/auto trans kickdown linkage is neater and requires less screwing around with a Holley on a Cleveland or any Ford V-8 for that matter. And for reasons I will not get into a Holley will work better on a Ford.