Corvair Forum

Took the car about 2 miles to the coffee shop. When I came out it started normally but then started to run rough. I could keep it running by pumping it but it would eventually quit. Tried this several times. It was like fuel starvation, but I know I have gas.

I called for a Tow and then decided to try once more. It started an kept running although a bit rough. After about a mile of driving it smoothed out and was running normally by the time I got home.

I have put a seneral hundred miles on this car since I got it about a month ago. I guess I have run at lest two tanks of gas thru it.

My pilot training makes me wonder if it was carb ice. The conditions are perfect for it here today, but normally that wouldn’t happen right at start up.

So, what do you think? Fuel pump failing? Clogged/dirt in fuel filter? I have not looked at anything yet. I do plan to start it again in my driveway to see if it does the same thing.

Thanks
Rich G

Well, you have provided almost no specific clues and you apparently have only owned the car for a short time so you probably have little knowledge of the car's prior history or maintenance schedule. I can point to a few things to look at, but we also know very little about you or your background as a DIY mechanic. The videos below provides some basic instruction for performing a tuneup that includes an exploration of the car's operating condition. Since you have only owned the car for a short time it would be highly advisable to perform a complete tuneup including a compression test of all cylinders, a careful examination of all vacuum hoses and connections to check for vacuum leaks, a fuel pump test to check for proper pressure and fuel volume delivery to the carburetors, and examination of the ignition system to check the condition of the ignition points, distributor cap and rotor, and the timing and dwell settings, etc.

Your comments also sounded like you were starting the car in a very cold climate, since you suspected carburetor icing to be a possibility. If the automatic chokes are not properly set, it might be quite difficult to start the engine in a cold environment if the choke mechanisms are sticking or not adjusted properly. Pumping the gas pedal repeatedly has the effect of causing the accelerator pumps to repeatedly squirt fuel into each carburetor throat, which is a poor way to enrich the fuel/air mixture (as the choke butterfly valves should be doing if they are functioning properly). The choke mechanism fast idle cams may also not be in play if the choke mechanism is not working properly. The combination of a mechanically enrichened fuel/air mixture and a mechanically increased idle speed are both critical elements for cold engine starting and operation. So checking the choke mechanism for proper function and adjustment on both carburetors would be a significant part of a complete tuneup for your Corvair.

If fuel starvation was an actual problem, pumping the gas pedal would not be of much help because the float bowls would likely be nearly empty. Since pumping the gas pedal did seem to help some, testing the fuel pump may only confirm proper operation. However, since you are a new owner it may be a worthwhile effort to completely test and evaluate the fuel system and the ignition system.

The standard in the shop manual states that the pump should be able to deliver 1 pint of fuel over a period of 40 seconds or less at engine cranking speed. If your pump does not appear to have any leaks and can pass the output pressure test, but fails to deliver the needed fuel volume, the problem may not be with the pump itself. There is a long fuel line that runs the length of the car from the fuel tank to the fuel pump. In order to pressurize and deliver fuel to the carburetors, the pump must be able to create a continuous vacuum in that fuel line to draw the fuel from the tank to the pump. Most of the fuel line is made up of steel tubing and is unlikely to develop a leak. However, there are two short lengths of rubber fuel hose in the fuel path. One section of hose is found at the fuel tank outlet, while the other is found adjacent to the starter motor — just before the line enters the engine compartment. The purpose of the second hose is to absorb vibration from the engine and prevent it from reaching the rigid steel fuel line. If either one of these two hoses develops a leak, the leak itself may not be apparent because the line is not under pressure so fuel will not be forced out. Instead, the leak amounts to a vacuum leak, which can allow air to enter the fuel line. This can prevent fuel from being drawn from the tank to the fuel pump, much like you might experience with a drinking straw if the straw was to split and developed an air leak in the side of the straw. What appears to be a faulty pump that is causing fuel starvation problems in the carburetors often turns out to be a leak in the fuel line at some point between the gas tank and the fuel pump. So if fuel starvation becomes a problem with your carburetors, there is a tendency to question the condition of the needle and seat valve inside the carburetor, or to blame the fuel filter at the carburetor inlet (thinking it is clogged), or to blame the fuel pump itself. Before you blame the pump and toss it, or abandon it and replace it with electric fuel pump, be sure to check the condition of the rubber fuel hoses at each end of the long fuel line between the fuel tank and the fuel pump. You may find that a couple of hose clamps and a few inches of replacement fuel hose is all that necessary to get you back on the road!




If you don't have access to a 1961 Corvair Shop Manual and the 1962-1963 Shop Manual supplement, they may be downloaded using the following link…

Common and Useful Corvair Websites

viewtopic.php?f=225&t=6007

Watching the video presentations below helps to provide insight and understanding about proper sequencing of the tuneup steps and procedures. Skipping around can insert obstacles and problems with getting the engine properly tuned.

The portion of the first video segment toward the end (Part 1, 5:10) and at the beginning of the second segment discusses throttle linkage adjustments and carburetor synchronization.

Tuning the Corvair Engine — Part 1



Tuning The Corvair Engine — Part 2





I would like to encourage you to expand on your earlier post and tell us more about yourself, as well as about your Corvair. If you can provide your personal assessment of your mechanical skills and abilities, that would help a lot. Members of the Corvair Forum love to be helpful in assisting other Corvair owners with technical support and advice, but it helps a lot if we have some understanding of your technical background and mechanical abilities, your Corvair-related knowledge, etc. Helping us to know more about you will help us to write comments to you that are tailored to your needs and experience. Knowing your specific location is also useful, because knowing where you live can sometimes suggest possibilities.

I have attached copies of several reference guides, shop manual sections, and shop manual supplements to help you. Please let us know what you find or if you have any further questions.

I have told you about myself twice so far. Once the first time you asked me and once in the introduction. If I somehow through psychic powers knew what was wrong, I would have fixed it already. I was just iooking for a few comments to based on previous experience of owners. I know what to look for but there may be others who could lead me down a shorter path.

So, for my final post on this forum

I am 72 years old. I live in NY where it is 60 degrees today.
I own a 1966 Corvette which I maintain myself
I own a 1968 Corvette which I maintain myself
I have owned seven airplanes and have rebuilt an entire 1946 Taylorcraft including the A65-8 Continental Motot
I just finished a top overhaul on my Bonanza IO-520 Continental with new Cylinders, pistons and all that goes along with that

When I bought my first Corvette 18 years I joined NCRS. I didn’t know much about those cars then but I bought every book I could, including shop manuals and through the help of their technical discussion board, became fairly competent at diagnosis of issues. I have done the same here. Owning shop manuals, joining CORSA. And asking what I thought were reasonable questions from a new owner. And yes, I’m obviously a new owner because I’ve said so at least twice on this board.

So, rather than deal with responses that assume I’m an idiot because you don’t know my background in sufficient detail, I’ll sign off.

What was the temperature when you drove it? I'm guessing fairly cool since you are suspecting ice. It really sounds like vapor lock but that would normally happen when it's hot outside and the engine is really hot.

It could possibly be some debris in the fuel system or carbs. It may have been blocking a fuel passage or line and became dislodged and now the engine operates ok. This may recur if debris is present in the system. If you have not inspected the inside of the tank, fuel lines, fuel filters, and inside the carbs for debris, I suggest you do so and make repairs as necessary. These cars often have fudged up fuel systems from sitting around to much and the tanks if original or old often have a lot of crap and corrosion in them that can block proper fuel pickup as well as get thru the system to the carbs if the pickup sock is not intact.