Jetting on Holley 350 cfm 2 bbl

[Anonymous]

Has anyone written up a page or article on jetting specifics for the Holley 350 cfm 2 bbl for the 200?

In the strictest sense this is too much carb for a 200, but I'm also at about 4000ft altitude, and it's going through the log, so....

I suppose what I'm cocerned about is over-carbing. That is the situation right now with my 302. The previous owner threw on a Holley 650 carb, that was set up for a 454 Chev engine. I've jetted it way down, changed the secondary rates, reduced the pump shot, and it's still a rich running, tough to tune pig.

A mild 302 like mine really only needed a 500 cfm carb (actually 480 cfm at 100% volumetric effiency rate, yeah right, try 425 at best) but you know how us hot rodders think, right?

 

[Anonymous]

I used 53's on the 350 cfm Holly I had in my 260. When using a 500 on my 390 I used 64's. So I think I would start with 50. I hope that helps and good luck.

 

[wsa111]

Monkeyracing, The 350 cfm holley 2300 series carb is my next project to fine tune. I am at 50 feet above sea level where i live subtract at least 1 jet size for where i plan to start.
First of all the 350 carb really flows 255 cfm @ 1.5" when using 4 barrel holley standards. This carb is not to big for a 200 engine.
Right now i have a 500 cfm holley-4412 on my engine. I have that jetted so the throttle response is very crisp.
I plan to start with 59 jets,8.5 power valve & an orange cam in the #2 position using .028 accerator pump discharge nozzles.
I plan to try the smaller carb to see if performance is close to the 500 & fuel miliage that much better.
After i get the 350 carb on my 200 i will be able to give you precise advise. Start with where i plan to start & you will be very close. Carb tuning is a trial & error method & if you have available air fuel ratio info its that much easier. Let the forum know your results.
Make sure you have at least 6-7 lbs of fuel pressure to the holley & the correct float level or other wise you will be richining the settings trying to cover up a fuel delivery problem. William

 

[Mustangaroo]

First off, the Holley 350 2v, only produces about 258 cfm when using the 4v formula for doing the CFM. The Holley 350 is not too big for the 200 six. But you have to tune it correctly, a small jet is not allways the answer. Often the power valve is too big and is causing the engine to run too rich. The stock power valve is a 55 or 65 the lower the number the sooner it opens to allow more fuel to flow, I use a 85 power valve, it stops the engine from stumbliming and bogging from a too rich condition. The accerlator pump is another area that must be looked into, the Holley 350 accerlator pump is a 30cc pump, the Holley 500 is a 50cc pump, again go with the smaller pump and tune for best performance. Speaking of tuning one way to tune your Holley carb is with a Vacumn gage, just conect it to your manifold vacumn and adjust your air and richness settings for the max vacumn reading on the gage. Most sixes with a stock or mild cam will read 18-20 inches vacumn on the gage, larger or lumpy cams will be lower in the 14-15 inches of vacumn range. Remember no matter how large of carb put on your six, it can be tuned to run correctly, it my not use all the cfm the carb can flow but the six will use all the carb that it needs and then doesn't use more if tuned correctly! I'd start at 58-60 jets on a 200 six, check you plugs for lean condition and adjust jets as needed. Good luck and have fun, the Holley carb can drive you nuts if you let it!

 

[wsa111]

You & i are on the same recomendations on this 350 carb, but i think you really mean is the 8.5 power valve to prevent a leaness in the fuel curve from cruise to full throttle. Often with a small engine a 6.5 power valve leaves a lean hole which will cause part throttle hesitation.
I am using a 2 stage power valve on the 500 cfm to cover the void between 9-2.5 " inches of vacuum. I still have more testing to perform but this seems to be the slick setup on the 500 carb. When i am satisfied with this combination i will post it.
I know 2 stage power valves are for non performance vehicles, but these six cylinders do not require the maximum flow from the power valve circuit & will fill the lean hole between 10-3" of vacuum. so far in testing it has proved suscessfull. William

 

[Anonymous]

...the Holley carb can drive you nuts if you let it!

Yeah, I hear that. I almost gave up on them for a while. I've gotten pretty good with the 4 bbls, but 2 is a whole new thing for me.

Part of my 'bad' experience probably comes from the fact that all the Holley carbs I've ever owned were used, and I had to find ways to adapt them to whatever I was using them on.

Thanks for the advice. I never would've thought of using the 8.5 power valve. I probably would've started smaller than that. I guess that's what happens when you've never built anything smaller than 300 cubes.

Jim

 

[xctasy]

56 jets on a 350 #7448are okay to give 125 hp net. The power valve on a modified engine certainly needs to go down to 6.5 or 4.5 if you run a big cam. Wills advice looks great for a stocker.

This allows you to run quite lean most of the time, and richen up only under wide open throttle.

 

[Anonymous]

I gave up on putting Holly's on daily driven street cars. They didn't run right most of the time and it seemed that when I finally got it tuned just right it was out of wack by the next weekend. The only one that was reliable was the 1940 I had on my six, and it suddenly had a problem withe float sticking to the bowl. I spent three hours trying to fix it; now it's in the junk box.

 

[Mustangaroo]

Will,
You are correct it is a 8.5 power valve, I referred to it as a 85 because if you try to find 8.5 on a power valve you never will The power valve is numbered with one number each on each side of the valve, so you only see the 8 on one side and the 5 on the other side! Now when you go to your local parts house to buy one remember to ask for a 5.5, 6.5, 7.5, 8.5, 9.5 etc,etc,

Also the main reason so many are having trouble tuning a Holley Carb is because of 6 tuning points, they are:
1. Air mixture (screw)
2. Richness mixture (Screw)
3. Jet size (58,59,60,61,62,etc,etc)
4. Power valve size (5.5, 6.5, 7.5, 8.5)
5. Accelerator pump size (30cc, 50cc)
6. Accelerator pump (adjustment arm screw)

Too many try to just adjust number 1,2 and 3 to tune their Holley, and that's only half of the tuning process! Most racers love the Holley carbs because it is so adjustable, that you can make it run on almost any setup!

 

[wsa111]

I'm doing testing on the 4412-500 cfm carb & the 350-7448 carbs.
After road testing the 350 carb it had a lean spot on full throttle acceration. I went from the .028 accerator discharge nozzle to the stock .031 nozzle, flat spot is gone. See my previous posts.
http://fordsix.com/forum/viewtopic.php?t=17205
I also plan to try a .029.5 custom nozzle in the 500 cfm carb & then the .031 nozzle. The .028 with the blue cam seems ok but i just want to cover all possibilities. William