I put a 670 CFM carb on my 350 and the plugs fouled in about 3 weeks. Using the calculator on the Holley web site I should be using no more than 607 CFM. Rounding down, and they are steering me towards a 600 CFM carb.

If you look at the intake. carb and cam combos in magazines like Summit they suggest that for the Voodoo cam and the intake I have I ought to run a 670 CFM Street Avenger.

I'm no carb expert and guys who tell me they are point out the the carb, cam and intake combos Holley suggests do not match the CFM caculator on their own web site. One guy even swore that the 570 CFM Street Avenger is the best for SBC.

Love to hear your thoughts, folks.

Thanks,
Tony

What calculator did you use? Also, efficiency comes into play with those things. Depending on the efficiency of the motor....and how hard its actually being run will dictate the carb you need to an extent. Either way.,...those are just rough estimations at best(those calcs)! The CFM rating is all about airflow....a fuel flow problem can surely be completely unrelated to how much air the carb can move.

Give me a 2 barrel and I can mess it up in such a way that it drowns your motor with fuel. On the other hand, give me your 670 and I can make it run out of gas at 4000rpm! Not that Im a carb wizard or anything. Thats not what Im saying at all. What I am saying is that its all about the tuneup. What power valve is in that thing and what kind of vacuum are you making at idle. Whats the fuel system setup, do you have a regulator(if necessary), and have you checked the floats lately? Any dirt in the needle and seat? Have you messed with the idle mix? Could be many things. And of course, it can even be things unrelated to the carb as well.

Even though the calculator dont think its perfectly optimum....thats a good guess at best. There are too many variables, and even if it had em figured out...you can just look at a motor and guess the efficiency it runs at during a particular RPM. I think its perfectly fine for that engine, it just needs some tuning. Ive run the 670 street avenger on top of a 350 poncho(real mild setup) with no probs. It was stock, stock heads, 8.8:1 compression, a crappy torker intake, and a mild 272 degree crane old school hydro cam. But it ran just fine! That same carb made its way on top of a little hotter of a 327(ported fuellies, hydro roller cam, good intake..10ish to one comp)....and it worked with that well after some tuning.

So, dont let anybody convice you that your carb is too big. Like many carbs, its pretty flexible and will adapt to more or less engine if necessary. Work with it before you spend money on something else.

What kind of plugs do you use? In my car the Autolites with the cut back electrode never lasted as long as good ole AC Delcos. We ran a 750 on my sons 355, they can be made to work.

Hate to say it, but carbs are almost never a plug-n-play deal!

Do yourself a favor, get a decent Holley carb book and learn to tune it inside out. It'll save yourself a lot of headaches down the road!

Could really be a number of things... too much pressure, floats not adjusted right, wrong size jets, wrong squirter, bad adjustment on pump shot, etc.

Without more info, I'm afraid we can't be of much help.

Good luck,
BC

I appreciate the comments.

It is a 6.5 power valve.

I'll have to go back and check the vacuum at idle.

I am not using a fuel regulator. We tested it and it came back at 7 psi so we felt we were okay without it.

The floats are okay.

We are going to check, tonight for dirt. I have a filter before the fuel gets to the fuel pump.

The plugs are Accel header plugs. The ones in the engine now are blackened from what I assume is too much fuel so I'll replace those tonight too.

Tony

What size primary jets are you running ? I'm running a 600 Holley on my bracket Vega (355) I paid $50 bucks for it and rebuilt it (Holley renew kit) then played with jetting and it works great. Have you checked the Mortec website for baseline Holley jetting ? it's a good place to start with your Holley.

In most cases, plug fouling occurs on the idle circuit and your problem might just be a mixture screw adjustment. You didn't say which heat range plugs you are using (or the cam specs or idle rpm). Unless you're running high compression and high rpm, ac 44's (or same heat range in another brand) are good, 45's if lots of idle time and low rpm use. Larger cams need a higher idle speed than stock. Their lower vacuum draws less fuel but that fuel doesn't atomize properly (and that's why they sound so good :)) and you wind up with wet plugs.