Recently pulled out one of my TR8s that ran great when it was put away. It starts right up, but it won't idle. Depress the throttle and you see gas squirt into the front 2 barrels. It will rev up as it should and will continue to run as long as you slowly pump the throttle. Let off the gas and the rpms drop quickly then dies. Once the engine warms up, it gets worse. Carb in question is a Holley 390 with vacuum secondaries. Pull the carb and try to clean the idle circuit? Went thru the ignition system to make sure that wasn't the problem. Spark isn't the problem.
It's just about got to be clogged idle circuits. Quick clean up: the idle screws are in the side of the front metering block. Turn them in, counting turns, till they stop. Then take them all the way out.
There will be a cork ring that seals the idle mixture screw, pull them with a O ring pick, bent paperclip, etc. Now use a can of carb cleaner with a tube on it, stick the tube in the hole and blast for 2-3 seconds. Do this 4 or 5 times, then let things sit for 15 minutes or so and then blast again as ou did the first time.
Open the choke flap and you will see 4 small holes at the front edge of the venturis, those are the idle air bypass passages. Blast them out as well.
Reinstall the idle mixture screws and their cork seals, turn them in till they stop and then back them out to the setting you found in the first step. Now start the engine, carb cleaner will make it run rough for propbably 10 or 15 seconds, maybe as long as a minute so you'll think the idle passages are still plugged.
When you turn the mixture screws, in is leaner, out is richer.
From the Holley tech web site:
QUESTION How do I adjust the mixture screws on my carburetor?
ANSWER To set idle mixture screws: 1. Get the engine up to temp. 2. Shut the engine off. 3. Install a vacuum gauge to a full manifold vacuum port. 4. Turn the screws all the way in until lightly seated. 5. Next, back them out 1 full turn and restart the engine making sure the choke is completely off. 6. While at idle, back them out 1/8 turn at a time, alternating between the 2 or 4, until highest vacuum is achieved. Be sure you keep all 2 or 4 screws even. You can also do these adjustments without a vacuum gauge. The adjustments are the same except you will adjust to highest engine RPM at idle.
http://www.holley.com/TechService/FAQ.asp?category=Carburetor
Thanks mudg. Worked like a charm. Fired right up and settled back into it's usual smooth 800 RPM idle. No spits no sputters after the carb cleaner made it's way out. I said it before and I'll say it again. TR8s don't like to sit. They like to be used and abused often.
Now with 10% ethanol in the gas, cars with carbs that sit get gummed up very easily
Great post Curmudgeon ! ! !
Bookmarked the page for the next time a Holley stops working.
Glad to help! OBTW, I've used that same method on Webers, Dellortos, Solexes, Mikunis, Nikkis, Rochesters, Carters, in short anything with a removeable idle mixture screw.
