Troubleshooting Carburetor Problems and Vaporlock Blues Revisited

I had some conversation with Mike Porto, CA. member, and a note from Robert Knight, of Ohio fame, concerning the operation of their cars under certain driving conditions. That is the polite way of saying: Why did the thing stop running when everything seemed fine?

Summer is here and those members in the snow belts get to fire up the Packards and hit the roads free of salt and the wonder why the car may have a miss, seems to starve for fuel, smells like gas is all over the place, or cannot see gas in glass bowl, or the car dies at normal running temperature after a good high speed run and you exit the highway. New fuels are here.

Back in the Fall 2002 issue of the News Counselor, Q-Tips had an article, by Roger Gibb, concerning vapor lock. You want to review that article when you discuss vapor lock.


There will be no discussion about drilling for oil, Green whatever, politics, gas companies are making a killing, or any statements like-“Well that is stupid, a clean burning fuel can be made without any additives”. We have to work with what we have and we have old cars that use carburetors, using fuel that the cars of old were not designed to use.

The use of fuel or additives containing excessive amounts of ethanol, methanol or MTB, may cause damage to fuel system components and can cause the vehicle to run lean. In other words, it acts as if the engine is not getting enough fuel. Even the owners manuals for “Modern Cars”, with fuel injection systems that operate with 30-40 pounds of pressure, state not to use fuel with more than 10% ethanol. What happens with modern fuel is the boiling point is lower, and you can get vapor lock even when the engine temperature is normal. Can you raise the boiling point? Well you can put in about 8 ozs of Marvel Mystery Oil per 20 gallons of fuel, or kerosene of the type sold by ACE, 1-K Grade fuel under the ACE number 12030, can be used at a rate of 16 oz. per 20 gallons of fuel. Much more and you may look like the Queen Mary under full steam and you may foul the spark plugs.

Now if you do not drive your cars much, or for long periods, you may not have problems. However, I have one Packard I have owned since 1970 and in those early days it never vapor locked until we got our California “clean” burning fuel. Well, OK, so you add an electric fuel pump. For you 6 volt Packard owners the Airtex Fuel Pump Model E8011 is a good 6 volt draw through pump. The E8011 pump will allow you to keep the regular pump and you can put a switch under the dash so you can turn the electric pump on when you need to force fuel, that is boiling, to the carb.. Remember you are positive ground for the hook up.

What are some indications of vapor lock and maybe other problems with your carburetor?


The most common reasons for flooding are:

1. The engine is started and fuel flows over the top of the carburetor, or pours into the intake manifold. This condition is generally a result of either dirt between the needle and seat, or a stuck float. A light tap on the fuel inlet fitting will sometimes cure this condition. Remember, you are about to tap “OLD POT METAL”. Note: a light tap means no hammers and the engine should be running.

2. The engine is shut off and the fuel drips down the barrel(s) of the carburetor. This condition can be caused by the fuel line being located too close to a heat source such as a radiator hose or exhaust manifold. Well that is us sports fans. Heat shields can help, remember we want to try and lower the boiling point of the fuel. Heat can cause the fuel in the line to expand and be forced past the needle and seat causing flooding. Also fuel can boil inside the carburetor as the result of improper or missing gaskets or spacers between the carburetor and the intake manifold. If the heat riser is stuck in the closed position it will cause excessive heat under the carburetor and boil the fuel causing flooding and hard starting when the engine is hot.

3. When there is excessive fuel pressure. Excessive fuel pump pressure can be caused by a defective or worn out fuel pump. This condition will cause flooding. Three to four pounds is about all you should need.


1. WHEN THE ENGINE IS COLD: Check for proper choke operation. When the engine is cold prior to starting, press the accelerator down to floor and release. This should cause the choke plate to close. When the engine starts, the choke should open partially and continue to open as the engine warms up. . .When the engine is warm, (full operating temperature) the choke should be fully open. And for the non-automatic choke cars, make sure the manual choke is hooked up properly. Push the choke knob in as the engine warms up.

2. WHEN THE ENGINE IS HOT: Excessive heat around the fuel system is indicated. (See “FLOODING” item 2). You can smell gas-remember if the gas is boiling you are smelling the gas vapor not the liquid fuel.


Check engine vacuum using a vacuum gauge. Gauge should read approximately 18 inches at idle. If vacuum is low, check condition and location of all vacuum hoses. Check carburetor base gasket and manifold gasket. Run an engine compression test. Worn engine parts such as valves, rings, or camshaft will cause a rough idle. Look at the ignition system (plugs, wires, cap and rotor). MAKE SURE THAT THE IDLE MIXTURE SCREWS ARE PROPERLY ADJUSTED. Remember: You must flush the fuel pump as dirt or rust in the carburetor will cause a rough idle. To check the carburetor for air leaks you can spray it with carburetor cleaner and if the engine rough idle smooths out you have an air leak. Now do not do this with a super hot engine, and if you have a painted carburetor kiss the paint good-bye.


Also, check the ignition system and the timing. Make sure that the distributor advance mechanism is functioning properly. Other problem areas include cracked or improperly connected vacuum lines or a clogged exhaust system. Excessive alcohol content or additives in the fuel can lean out mixtures enough to cause a HESITATION or engine surge.


Check for miss-adjusted fast idle cam screw, or idle screw. Check for proper operation and adjustment of all linkage on the carburetor. Check choke operation and make sure the base gasket is properly installed.


It is nearly impossible for a carburetor to cause a vehicle to backfire. However, too lean a mixture setting can cause backfiring when you first start a car . Make sure that the spark plug wires are properly attached and that the distributor cap is free of any carbon tracking. Check the ignition rotor to make sure that it is in good condition. Set the ignition timing to specifications. Check the manifold vacuum with a vacuum gauge. A bad vacuum leak can lean out the mixture enough to cause an engine backfire. Check the engine compression. A leaking, burned, cracked, or stuck valve could be the cause. A worn camshaft lobe or bad timing chain could also be at fault. Check the choke operation. If the choke comes open too quickly, the engine will be lean when cold and backfire.


Check the heat riser valve in the exhaust manifold. It should, be closed when cold. Also be sure that the choke heat tube that is in the manifold is not allowing exhaust gases to enter the choke housing. This will cause the choke to open prematurely. Make sure that the choke pull-off operates properly. Restricted or clogged crossover passage in the intake manifold will affect the choke operation. For manual chokes make sure the linkage is operational and do not forget to push the choke in when the car has started to warm up.

Now how do you clean all that gas and carburetor cleaner smell off your hands? Wash your hands with tooth paste. Yep, that will get your hands kissing sweet.

Packards International Motor Car Club, 302 French Street, Santa Ana, CA. 92701 phone: 714 541-8431, office hours: 9:00 am to noon CA time

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