C3 diagnosis revisited

[Gary S.]

Hi to all. Earlier this month I posted the following concerning my 72 LT1:

"I drove the 200 miles from home to Carlisle and the 72 LT1 ran beautifully at highway speed of around 65-70 mph. Driving the stop and go traffic from the turnpike to the fairgrounds on route 11 was another question. It idled in a less than an impressive manner and bucked occasionally."

Well, today was my the first day with spare time since Carlisle and I looked at the carb and engine. All vacuum hoses, fuel lines, etc were tight but there was evidence of fuel from the front and rear bowls, dripping onto the intake manifold. I checked the bowl screws and they were not as tight as I would have expected. I can tighten them fairly easily but wondered if there was any torque value on bowl screws? I am afraid to over-tighten them for fear of stripping them. Yet the fuel is dripping/seeping out. The carb is a Jerry MacNeish (sp?) recent rebuild and this is my first trip in the car with it installed. In addition, I checked the float levels and they are fine, tending towards a micro-smidgen high versus low. That is, I can rock the car from side to side and get fuel to seep or dribble out of the float sight hole. Also, the carb mounting bolts weren't very tight so there is a slight possibility that there was a vacuum leak.

Any ideas? The bowl gaskets appear to be the original brown style versus the newer, non-stick blue type. Should I use Lok Tite on the bowl screws? The carb is original to the car, btw.

thanks as always,
Gary

[Jim T.]

Re: C3 diagnosis revisited

My Holley performance carburetor installation and adjustment instructions list tightening the fuel bowl screws 25-30 inch pounds.

[Gary S.]

Re: C3 diagnosis revisited

Jim, great information. Thank you.

[Gerard F.]

Re: C3 diagnosis revisited

Gary,

Here's my story with a 67 restored Holley, which I think had similar sympthoms to yours, for what its worth. I finished my holley restoration (this is the one that was in the dishwasher and the crockpot sometime back) and got every little orefice and jet to holley spec and put it back on the engine last weekend.

I took a run with it and it ran great at high speed, with a slightly elevated temperature. But when I got back into traffic at slow speed and idling for a while the temperature elevated to 200 (I now keep a dedicated meat thermometer taped to the radiator hose to check my gage) and then started idling rough.
I pulled the air cleaner and found gas dripping into the secondary side of the air horn.

It sat most of this week and today I took my same run with the AC blasting to try to repeat the elevated temperature.(I'll admit it was a little cooler today, about 85). It ran just perfect, got up to 180 and finished off at 170 in the downhill run. No elevated temperature at idle.

From this, I guess that maybe the base gasket has to take a set on the manifold to seal the vacuum leaks. Perhaps also, the elevated temperature at idle is enough to boil off the gas in the secondary fuel bowl which just sits there at idle. This is just my guess, I'm a tinkerer, not a mechanic.

Also, I did use the blue gaskets on the rebuild, and have had the fuel bowls off and on a couple of times without a leak. The fuel bowl screws were just a little more then hand tight with a screwdriver, not overly tight. I also used those plastic fuel bowl screw washers.

Hope this helps

Jerry Fuccillo
#42179

[Mark #28455]

never use locktite

NEVER use locktite on the Holley screws or you'll hate yourself when it comes time to service it later. It was quite common to need to re-tighten the fuel bowl screws once or twice when using the old brown gaskets. In addition, it may also be leaking from the accelerator pumps on the underside of the fuel bowls. As noted above, the torque value for all of the bolts/screws is quite LOW (just past snug) as they screw into pot metal and are easy to strip!

Your fuel level in the bowls is fine - the factory probably never got it all that close.

This also points out why the factory used Q-Jets on most of the passenger cars - not very sexy to look at, but they don't act up like the Holleys can (only one internal fuel bowl that is essentially cooled by the airflow around it).

Good luck,
Mark