66 L72 idle problems when hot Holley Carburator

[John M.]

Hope someone can shed some help! When I first take her out she runs perfect then after I shut her down for 15-20 minnutes she will start back up immediatley but will not idle. It will run hard at any constant speed until she comes to a stop, then I've got to keep my foot on the gas lightly to keep her from stalling, seems to run out of fuel but will immediatly start back up. I feel it must be a carburator problem.

I have noticed that my holley carb sometimes will leak gas somewhere around the rear main gasket but only when the car has been sitting not while running. It has been very hard to dertermine where it is leaking!! Do I have a gasket problem or a stuck float?? Anyone have any experience with these carbs.

I have checked the timing and vacume. All seems fine.

[Joe R.]

Re: 66 L72 idle problems when hot Holley Carburator

John,

Your carb seems to be effected by what is known as "Heat Soaking". The following things may be checked and help your problem.

1. check the float level as it may be too high and boiling over
2. check the base gaskets and make sure they are installed correctly

More radical if the above doesn't help

1. place a set of spacers between the intake and carb
2. block the heat riser with a gasket made for that purpose (these are included in some intake kits)

If the above doesn't cure your problem move it on down the road!

JR

[Timothy B.]

Re: 66 L72 idle problems when hot Holley Carburator

John,

When is the last time the carburetor has been worked on. Many times when these Holley's leak it's because of gasket sealing problems and because of there modular design problems can be like what you are experiencing.

Keep in mind 75% of the time the problems are ignition related so make sure everything is working good there before blaming the carburetor. There is good information in the archives about Holley overhaul but the important thing to remember is that all surfaces need to be flat and use Holley gaskets when assembling.

Have you tried to reset the curb idle and adjust the air emulsion screws after the hot soak, do these screws have an effect on the idle when it's hot? A very basic rule when adjusting Holley's is to make sure the primary transfer slots are only slightly exposed at curb idle like little squares, this keeps the transfer circuit wet with fuel but allows full control of IDLE A/F ratio with the emulsion screws. If you need more air for IDLE the secondary throttle plate screw can be turned to allow air.

[John M.]

Re: 66 L72 idle problems when hot Holley Carburator

Thank you for the great tips. Here I have pasted a tech tip I found on another forum regarding float adjustment. Is this the correct way to adjust the floats??

In order for proper fuel deliver there must be a proper fuel level in the carburetor fuel bowl. Whether it is a 1, 2 or 4bbl carburetor.

f the level is too low there will be a lag in take off or lack of power as the RPM increases. Sometimes there will be surging at cruising speeds.

If the float level is too high there will be flooding or fuel spilling over into the venturi of the carburetor unmetered.

For this tech tip we will cover the Holley 2 and 4bbl carbs with the sight screw on the fuel bowl, like the model 2300, 4010, 4011, 4150, 4160, 4180, 4500. All of these have a brass sight screw on the side of the fuel bowl. In the case if the 2bbl there is only 1 fuel bowl therefore only 1 sight screw. For the 4bbl carbs there are 2 sight screws.

Start the motor and run it for 30 seconds. Turn the motor off and wait 30 seconds for the fuel pressure in the fuel bowl to stabilize. Then remove the sight screw on the side of the fuel bowl. If the fuel trickles out then you are perfect. If it pours out then the level is too high. If nothing comes out then the level is too low.

If the fuel level is too high, put the sight screw back in the fuel bowl and loosen the screw on the top of the fuel bowl and turn the nut below it clockwise 1/2 turn and tighten the screw back down. Start the motor and run for 30 seconds. Turn the motor off and wait for 30 seconds. Then remove the sight screw again to see if fuel trickles out of the hole. If not, then repeat step until it does. Each time remember to put the sight screw back in to the fuel bowl to avoid fuel spillage.

If the fuel level is too low, follow above procedure except turn the nut counterclockwise and repeat above procedure until the desired float level is achieved

I followed this proceedure and first found that both of my floats were two low. I was able to get the secondary float high enough so that fuel was just up to the expection hole. But I cannot get the primary to come up that high. The fuel is still below the expection hole.

After adjusting the secondary float I noticed I still have fuel leakage around the driverside lower screw that holds the float bowl to the carburator. I have thightened and it still leaks. It does not appear to be leaking around the main gasket just around this screw. Any ideas as to why???

[Duke W.]

Re: 66 L72 idle problems when hot Holley Carburator

... sounds like the classic hot soak problem that many owners are having due to the lower mid range boilling point of E10 fuel.

The first thing to do is check that the heat riser moves freely, then WIRE IT FULL OPEN. Next convert the ported vacuum advance to full time, which will reduce waste heat at idle and low speed driving and also reduce around town fuel consumption.

If the above doesn't solve or at least mitigate the problem sufficiently go on to other more the complicated, expensive and time consuming changes, but start with the easy, inexpensive fixes first.

Duke

[William C.]

Re: 66 L72 idle problems when hot Holley Carburator

With respect to the leak, do you have the gasket installed that goes under the screw head where it enters the bowl, and is the gasket fresh (as in new)