Holly Carbs

[Bill W.]

Hello people, I have a problem with the Holly carb (List 3367) on my 1966-L-79. Within the last few months the idle quality has gone south. The engine is equiped with T.I. that is working properly. The idle has gone from 800 RPM with a slight lope to 500 rpm and very rich smelling ext. If you re-adjust idle speed and mix screws to proper specs, within 10 miles of driving, the idle is up to 1200-1300 rpm. There is now a "flat spot" just off-idle that wasn't there before. Engine has new plugs and still makes good milage on the road. What should I look for when I tear into this carb?

[Bill Baird]

Re: Holly Carbs

Mr. Wilhelm,

While I'm not specifically familiar with your carb., I've run a Holley 3310 on my 1975 coupe for nearly a decade now. Whenever I've had a rich condition with my carb. that defied a solution, it's always ended up to be one of my power valves (my carb. has two, not all do). This rich condition has at times been drastic (sucking through 3/4 of a tank of gasoline in 15 minutes on the highway) when the primary power valve totally gave out, to a mildly "off" idle when the secondary valve was just starting to go.

If you have confidence that your carb. is not particularly in need of a rebuild, and nothing else seems to grab your attention, I'd check the power valve(s).

Bill Baird NCRS #30428

[Roy S.]

Re: Holly Carbs

Bill,

Have you checked the idle air bleed or passages, some may call them the idle air vents.

[Joe L.]

Re: Holly Carbs

Bill----

I'd recommend checking the power valve, too. Your Holley list #3367 is a model 4160. It has one power valve located in the primary metering body(model 4150s have a primary and secondary metering body with one power valve for each). Power valves are the "Achille's Heel" of Holley carburetors. They may fail suddenly and repeatedly. Years ago, I had a brand new 1968 Chevelle SS 396 with L-78 engine. That engine had a Holley 4150 model carb. I once went through 6 power valves on a round trip from the San Francisco Bay Area to Los Angeles. When they fail, the car exhibits symptoms very much like you describe.

I once told a friend of mine that Holley doesn't need to make any profit on their carburetors; they can count on making a handsome profit on the replacement power valves you'll need.

[Wayne]

Re: Holly Carbs

Can I assume you checked fuel level in the bowl? Looked for leaks in vacuum hoses, vacuum advance mechanism? Ensured that the carb is snugged down on its gasket?

Holley's are really easy to rebuild, I'd clean it and put a rebuild kit in it while I had it off. Change your fuel filter(s), and accelerator pump (should be in the kit), and look for any crud in the bowls or jets from fuel tank rust or other sources. As suggested, a new power valve with gasket is probably good insurance too, and may not come with the zip kit.

[Everett Ogilvie]

Re: Holly Carbs

Bill,

I too have had rich problems with several Holleys when the power valve starts to go. It can richen the mixture everywhere, at all engine speeds.

Everett