I'm looking for an aftermarket carb for my '66 327/300 4 spd. with stock intake. I'm taking the original 3367 Holly off and going with something more reliable. It was rebuilt <500 miles ago and won't hold a stable idle. Suggestions are appreciated.

 

May I ask what troubleshooting you have done that is telling you that the carb is the problem?

Many times erratic idle is not the carb but possibly a vacuum leak, timing or a distributor issue.

 

send it to someone who knows what they are doing

 

AFTER rebuilding the Holley 3367 on R66, it is absolutely the best performing Holley I have ever used. It was tuned to the engine by GM.

Although I can recommend a Edelbrock AFB or Holley 600 cfm with vacuum secondaries, I would encourage you to do further troubleshooting to verify your problem is the carburetor regardless of the model. Check for vacuum leaks around the base plate and etc. Holley provides many videos to help and the members here will help if you can tolerate me and some others. https://www.holley.com/support/carburetor/
Also, the Chevrolet Chassis Service and Overhaul Manuals provide excellent help. Some mechanics consider throwing a kit in the carburetor a rebuild, but without checking for warpage and float adjustment, engine tuning, etc. it is just a cleaning. It could be an ignition or timing problem.

Here is a current thread with the same request: https://www.corvetteforum.com/forums...t-install.html and another with idle variation https://www.corvetteforum.com/forums...-throttle.html

If you are then wanting to replace your Holley, be advise you will still need to fine tune the new carburetor after installing it.
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PM me for a referral for someone in Tampa that can totally rebuild your carb. He has the experience (55 years), the parts and the air flow machines, milling machine, lathe and test mule engine to do the job. Jerry

 

Any other issues besides idle ? Do you smell fuel when it idles at whatever rpm it needs to sit there?
Do you have a Vacuum Gauge? At any above idle rpm . wherever if it settles down & holding your vacuum should be STEADY. If you're pulling a steady vacuum that's a good sign as far as intake manifold or head gasket leaks.
If I'm off on any of this below I'm sure one of the guys will set it straight.
Pull plugs. Clean or replace. Your issue can foul your plugs horribly and have you chasing ghosts...become another obstacle.
With motor off Set your Float Levels.
Motor Off seat each idle screw. Bring the idle screws out equally to 1 1/4 turn....start the car. Some may prefer 1 turn, others 1 1/2 turns as a starter ..no matter ...just hope it starts.
From there( if you get it running) every idle screw adjustment you make should be very small ( ie: 1/8 turn lean or fat) and always go to each side to ensure they're equal. Listen to your engine & keep the vacuum gauge on as you tune.
Timing: Many set timing at idle. It seems you may not be able to do that. But you can Power Time. Have someone rev the motor to full advance when it goes no higher...approx 3000-3200 rpm. Set your Max Timing There. Worse for your motor to have bad timing at higher rpm's than a sloppy idle. I usually Power Time then sort out my idling after. But yeah....you should ensure your at proper timing. Badly retarded can mess up idle & spark plugs.

PS: If you Vacuum is not steady a vacuum gauge's behavior patterns can mean different things. Most gauges have diagrams in the box to point at problems the gauge is telling you. Vacuum patterns can point to intake or head gasket vacuum leaks or always low vacuum can be retarded ignition timing.
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Good Luck .

 

The last time I put a vac gauge on it, it read on or about 14 in.Hg, which for my cam was good. It stayed pegged. Timing could be an issue but it runs great through the gears with no backfire or detonation...but i do have an overheating problem in stop and go Florida weather above 85º. That issue I've chased down as far as I can go except to have the timing looked at. The distributor was rebuilt by the same shop at the same time that rebuilt the carb. I went to a Petronix and the shop installed it wrong and it failed after 50 miles. I replaced the module and coil and it now runs well except for the unstable idle and overheating as mentioned. I've yet to find a reliable shop locally to check timing and as time marches on, I'm less able to bend over to do diagnostics, not to mention working in a non conditioned garage. After all the money, parts and diagnostics I've done, I assumed it had to be a sh*t rebuild on the stock GM Holly.

 

Thanks. In an above response, I posted what I've done in months past. During the summer months, it's too hot in my garage and driveway to do anything over a 210º engine and my back isn't what it was 37 years ago when I bought the car. I do have a neighbor whose kid wants to become a mechanic and shows an incredible knack for wrenching. I can hire him to pull the plugs etc. but when it comes to timing I'm at a loss. What I really need is a reliable shop I can take the car to check and set the timing and idle correctly. There is no shop in the Sarasota/Bradenton area that I know of. When the weather cools, I may take it to a shop Tampa Jerry rec's. Thanks again for taking the time to respond with the set-up details

 

Thanks R66. As always, your input is appreciated. My issue is finding a shop that's reliable, qualified and not a criminal enterprise. Any suggestions?

 

I understand you problem completely as I spent a year a Fort Stewart, GA and a year in Nam in the Delta. Illinois is bad, but you all have humidity all of the time.
If you have a willing helper, these cars are very simple to work on. You need the General's books to guide you and your willing helper / mechanic. Here are two to start with if you don't already have them:
https://www.workshopservicemanual.co...-repair-manual
Those books plus the Holley site should get you going. The on hands experience is here on the forum and also your local car clubs, it is just a darn ole Chebbie other than it wraps you azz in fiberglass.
Here is another great reference http://camaros.org/library.shtml Although it is on the Camaros.Org site, JohnZ was one if not the most knowledgeable members, if not the most, and the engines and transmissions are the same and he owned both. I am still learning at 77 from the smart guys. Your summer months are the best time to do your research. Don't forget the FAQ thread at the top of the C1 and C2 main page, there is a lot of information there.
A video of the engine running is always helpful. You can buy an inexpensive timing light, if you don't have one. Retarded timing can cause your overheating and idle problems. Simple float adjustments and vacuum leaks can add to it.
We need to know what engine and cam you have - 300hp or L79 or etc. The more information will get the best help.
One note: if you have let the car idle for any extended time, the plugs may be carboned up and you need to take it out and drive it for about 10 minutes at highway speeds.
Always start with a visual inspection: Take that fancy chrome cover off of the distributor (common source of shorts), fire it up in the dark and look for fireworks (bad plug wires, etc.). Then proceed with the basic tune up steps and basic carburetor adjustments (including float idle circuit adjustments). Check for vacuum leaks, cracked hoses, bad vacuum canister, distributor cap, wires, etc.
Your heating problem could be timing, clutch fan, lower hose, etc. There is a JohnZ article on Cooling 101 along with articles by other experts. 210*F is not hot in 85*F plus weather.
We'll help and if you are on a budget, you can buy a cheap timing light, multimeter (VOM), and basic tools for less than a trip the a "Corvette Shop" if you don't already have them.
Just my $.02 for what it is worth, can't buy bubble gum with it now.
Ron

 

R66- I've got all the GM manuals and printed out all of John Z's, Leif's, Duke's articles on timing etc. I have a vac gauge, dial back timing light (even the old school single strobe), VOM, distributor wrench yada yada. Carb adjustment is a more daunting task. My issue is the heat and the pain but I can take vitamin I to get thru the latter. As I mentioned I've beat the overheating thing to death on this forum. Everyone has helped and after replacing the radiator (Dewitts AL exact replacement),fan clutch (x 2), stat, sender, water pump, coolant, expansion tank cap, checked the all related hoses, wired the exhaust butterfly open, I think I checked every box except for timing. But it runs so well I'm having a hard time believing it can be that far off to cause overheating. It will heat well up 225º and possibly higher but I'll shut it down. So I've decided to just drive it when weather is cooler and not run the risk of overheating. But the unstable idle is a real pain.

 

I have understand being too hot (weather) to want to play with it? It was 99 here today and my garage is like 115+…

But I have always been told to check and set the timing first…. Then move on to carb adjustment, etc.

I also add a few degrees of advance over factory specs (I am usually in the 12-16 degree initial range) as factory specs were often a compromise
for emissions. That’s just as a starting point, but later verify total timing advance.

 

Fan clutch. Every "new" one I've seen is an emission type with 210*f lockup start. Some respond to spring clocking, most don't.

Finding a good shop to dial in your timing may be impossible. Best to bring in a set of target specs and have them implement them.

The Holley is most likely warped and leaking internally.