New carburator 350CFM vs 500CFM?
 

Been thinking about upgrading the carburetor on my truck. I have heard about the 500 CFM Holley being used, has anyone tried the 350 CFM model or is it not enough flow??? Anyone tried it out there?

Re: New carburator 350CFM vs 500CFM?
 

Don't waste your money on the 350cfm version, it doesn't make any difference from the stock carb. I've experimented with both the 350 and 500 cfm carb, the 500cfm will give a dramatic increase in performance and driveability.

Re: New carburator 350CFM vs 500CFM?
 

Thanks, just the information I was looking for.
My stocker is working, but I am not happy with the way it works. Fuel usage isn't great, about 9 mpg in town and best I have recorded is 11 on the highway. It just feels funny through the gas pedal, not working smoothly throughout the range. I do have another kit for it, I guess I will try that first since I already paid for it. Rebuilt a few months back, but I had to use the old accelerator pump piece.
What is selling me on the Holley is that it is jet-able, I have a Summit retail warehouse/store in the area, so it is no problem getting different jets to tune it.

Re: New carburator 350CFM vs 500CFM?
 

On the Holley you don't have to take off or pull the whole carburetor apart, just the front bowl when re-jetting.

Re: New carburator 350CFM vs 500CFM?
 

When I was looking at carbs, I see a 4412S and a 4412C, both look like the have manual chokes, any major difference?/

Re: New carburator 350CFM vs 500CFM?
 

One has the cadium plating that looks chrome, that's the difference.

Re: New carburator 350CFM vs 500CFM?
 

Thanks for all the information Big Block. Ordered one of them 4412 C as I don't like the looks of the shiny one as much.
Are there any issues hooking up the fuel lines and vacuum line for the distributor like thread pitch. Reason I asked, when I was looking at the Summit site, when you brought these Holleys up they listed some fittings like an AN6 with an inverted flare as something folks bought at the same time.

thanks again,

Re: New carburator 350CFM vs 500CFM?
 

I installed a 44121C on my 1966 GMC 3/4T PU,351 V6, I made the adapter for it. I also installed an HEI from an Buick V6. I had to lean out the carb a little. The GMC has 4.10 rear, AT400 and a gear vendor OD which drops the RPM's 500, I average a little over 12 MPG mixed driving. The engine starts much better and runs better, great up grade. I have to thank the fellows before me on this forum for the information. You will not disappointed in the Holley 500.

Re: New carburator 350CFM vs 500CFM?
 

Isn't there an adapter plate needed for the 305 as well to go with the 500cfm? Is it available on line or do you have to make one as Clyde did?

Re: New carburator 350CFM vs 500CFM?
 

The adapter is available from more than one manufacturer, the most common everyone uses is the Mr. Gasket #1937 adapter, TransDapt also makes one.

Re: New carburator 350CFM vs 500CFM?
 

You're existing fuel line fitting going in the carb will fit the Holley, it's up to if you want to bend up a new line or just cut the old one and hook up rubber hose to it. For the vacuum line there is a port on the right side of the throttle body but I prefer just to use the vacuum straight out of the fitting in back of the intake manifold. I first did the Holley conversion back in 1975 at the age of 15. it was so simple all that was needed to adapt it was basic GM to Holley 2bbl adapter since the 305's intake base shared the same dimension as most other GM engines equipped with smaller 2bbl carbs

Re: New carburator 350CFM vs 500CFM?
 

Got my Holley today and installed it in my truck. I had to get a special fitting to adapt my fuel line to match the existing inverted flare fitting on the carb. (part # BQ248) from a local outfit that make hoses.
Tapped off the back of the manifold for the vacuum advance, throttle linkage worked OK using the small hole just below the large 1/2" one.
After I got it started it ran good considering I didn't touch any of the adjustments except the idle screw.

After the truck sat for a couple hours and I went to start it, it was pretty hard to start compared to the old carb. Not sure if it is not getting enough gas initially to start. Is a electric fuel pump recommended to address this issue?

MY choke cable is too short, so I have to deal with that tomorrow. I have a longer housing and inner cable, if I am lucky I may be able to change those items. I really want to keep the original knob for the choke since it matches all the rest.

Re: New carburator 350CFM vs 500CFM?
 

Normally its because your getting too much fuel on initial start up. Have had that happen on my 66's 292...converting to an hei helps the situation.

Re: New carburator 350CFM vs 500CFM?
 

TJ, you are right about too much fuel. This morning I went to start the truck, didn't touch the gas, no choke and it fired up right away. It even idled good. I'm gonna love this carburetor.

Still pondering what to do about the choke, was thinking of moving it to the hole just to the left of the ignition switch. Then using the old location for one of those wiper delay units. if I can get the guy to answer my e-mails. Then get a radio knob from Brothers for it so it matches the rest.

Re: New carburator 350CFM vs 500CFM?
 

Should be able to used the stock choke cable. Not long enough maybe?

Re: New carburator 350CFM vs 500CFM?
 

The stock choke cable was too short. I ended up moving it to the hole that was blocked off next to the ignition switch. Now the cable reaches OK , plenty of slack to route it in the engine compartment. I installed the windshield wiper delay in the old choke location. Found a bezel that matches perfectly and a repro radio knob matches really good, especially after you paint it flat black.