I have a 76 350. Bought it right...replaced the interior and brakes, cleaned it up and it's a beauty! Engine #'s don't match. Present 350 was: bored .40 over to 357 ci. Pistons are cast with 8.5:1 comp with cast iron sealed power rings. Heads have 3 angled valve job -30,45,60 degrees with 1.94 intake and 1.50 exhaust valves that have been cut 30 degrees. Intake and exhaust ports have been matched and intake and exhaust ports have been opened up to seats. Holley 650 with 68 primary and 74 secondary jets. SSI cam #10311 has .465 lift with 224 degrees of duration@.050 and a 114 centerline. Crank is turned .020 on the mains and rods with oil holes chamfered. Bearing clearance is .0025 on the mains and /0015 on the rods. Bearings are Michigan 77. Hi volume oil pump. Double roller timing chain. Headers and SS exhaust.
That's how I bought it. Runs real strong. Whitout any determinable reason it runs great one day...or even sometimes part of a day and then it either won't idle or idles between 750 and 1500rpm, doesnt matter how I set it. Sometimes runs rough sometimes it's a kitten. Sometimes I cruise most all day on a tank of hi-test, sometimes I use half a tank on a 25mile ride! When that happens it usuall runs very bad...rough and no idle. It is not a constant problem. When this thing runs well it is a real fox. Idles great and sound amazing through the power band. I'm thinking the carb is a mess. Don't know where to go in western Ma. for a good Holley/Vette mechanic. I have done all my own repairs so far. This problem has me stumped. Any help out there?? John

Sounds to me like either a sticky flot or a sticky needle and seat. Could just need a good cleaning. You could try some carb/injector cleaner in the gas tank and see if that clears it up. Other than that a carb rebuild may be needed.

Here's a site about tune'n hollys.. http://www.mortec.com/carbtip1.htm that might help....i'm a edelbrock person myself.... Good tunnins for a holly ,and the site well help with anything ya ask about Holly........I would think about looking into vacume breaks .....from what ya said though!My2pens.....

|UPDATED|11/20/2003 9:33:51 PM (AZT)|/UPDATED|

Sorry to say,but from past experience,Holly carbs are junk.Good luck anyways.Hope everything works out for you. Edelbrock is the way to go.

|UPDATED|11/21/2003 8:21:00 AM (AZT)|/UPDATED|

It sounds like possibly trash in there. Probably needs a good cleaning. I took off an edelbrock to put a holley on my 350 after I rebuilt it, and would not go back to the edelbrock. If you want performance, stay with your holley, just tune it right.

I think Holley's may be a better pure performance carb as they are so adjustable for different uses, but because of that, people have to constantly adjust them. My local speed shop doesn't much like them as they can be so finicky. They like to sell Demon carbs...they call Demon carbs "Holley's that work."

For myself, I like Edelbrock carbs for the street, not pure performance. I think they're simpler, more reliable, and easily adjusted. I have a Brand X muscle car, and put an Edelbrock on it with excellent results. On my '78 L82, I'm running the original Q-Jet which I had professionally rebuilt, with no complaints at all.