If you own or are repairing a vehicle with a carburetor which includes most gasoline powered vehicles prior to about 1990 then diagnosing a no start problem is not quite as difficult as a modern computer controlled fuel injection system. The difference is that engines with carburetors don’t have as many sensors that can go wrong and this is in your favor.
The first thing to do when faced with a no start condition is to determine if the engine is getting fuel. This is true for both fuel injection and carburetors.
Checking The Carburetor For Fuel
The first thing you want to do is take off the air filter so you can see into the carburetor. Carburetors store a few ounces of fuel in a fuel bowl and when you depress your foot on your peddle this feeds a small amount of gasoline into the carburetor to allow for quick starting. Look into the plenum of the carburetor and pull back on the throttle actuator/lever or have someone pump the gas peddle for you. Do not turn the ignition key while doing this. You should see or hear or smell gasoline being squirted into the plenum. When you look inside you should see moisture. If you don’t see moisture or gasoline being shot into the carburetor then you may have a fuel pressure problem.
Checking The Fuel Pressure To The Carburetor
If you have an electric fuel pump which is available on some carburetor systems then turn the ignition key to the on position and listen for your fuel pump to prime the system. If you have a mechanical fuel pump that runs off the engine you will need to crank the engine for it to start pumping so make sure that your starter works by cranking the engine. Now to see if you have fuel pressure to the carburetor you will need to remove the fuel feed line at the carburetor. You should be working outdoors when doing this as fuel can spray from the fuel line at a significant pressure. You should also do this only on a cold engine and with a fire extinguisher near by. Now remove the line from the carburetor and for an electric fuel pump turn the key to the on position for 1-2 seconds and for a mechanical fuel pump crank the engine for a couple seconds. The rag should have gasoline on it. If it does have gasoline to the carburetor then you could have a stuck needle valve in the carburetor that isn’t allowing fuel to enter the carburetor. If you don’t have fuel pressure at the carburetor then you could have a clogged fuel filter or blocked fuel line or possibly a bad fuel pump.
Testing If The Engine Will Start With Staring Fluid
Honestly this might be the first thing you do to test if your engine can run at all but this is the step where you are going to use Engine Starting Fluid to replace the fuel that runs your engine. Starting Fluid is a combination of petroleum products including ether that burns very easily with a small spark. It only takes a very small amount to let your engine start and it is a good diagnostic tool when used properly. Do not try to do this with carburetor cleaner or brake cleaner only use starting fluid.
With your air filter off the carburetor spray starting fluid for 1 second into the carburetor plenum with the throttle actuator in the full open position to allow the starting fluid into the carburetor. Now immediately crank the engine and see if it starts. If it sounds like it is about to start but doesn’t then stop cranking and spray again for 1-2 seconds and try again. If the engine starts for a few seconds then you know that your ignition system is working and the car is not getting fuel. Do not run the engine very long with starting fluid it should either start the engine and allow it to run under its own power or it won’t. The chemicals in starting fluid are not really great for your engine and only a small amount of it should be used under testing or hard starting conditions.
If your engine has a mechanical fuel pump then it is possible that using starting fluid will allow the engine to run long enough and pump fuel to prime the fuel bowl on the carburetor. This is a condition that can happen when the car has been sitting for a few months and the carburetor has gone completely dry.
If your engine continues to run then you have solved your problem but you may still have problems if the needle valve in the carburetor continues to stick closed. You might find that the car starts and runs but then when it sits overnight it won’t start again. In this case you will need to rebuild the carburetor.
Checking Your Ignition System
Ignition systems on most carburetor system engines are pretty basic things and you shouldn’t be worried about diagnosing them.
The first thing to check is if your battery has good power. If you are cranking your engine for a long period of time trying to get it started then you probably ran down the battery. The same can happen when you leave your lights on or even if you have a clock or accessory that is draining power from your battery overnight. Most people can tell the difference in the way their engine cranks as it gets slower from a low battery. Turn off your accessories and lights to reduce the drain and close your door so the dome light isn’t on. This can sometimes give you enough power to get the engine to start. If not then you will need to charge your battery or attach a jump start to it to provide more power.
Testing the ignition system is easy with a timing light. If you have a timing light then connect it to your spark plug wire and it should blink as you crank the engine. Blinking is the voltage being sent to the spark plugs triggering the timing light.
If you don’t have a timing light then you can remove one spark plug and insert it into the end of the spark plug wire then rest the threaded end of the spark plug on bare metal not painted metal and have someone crank your starter. You should see a small spark at the spark plug tip. Bright light can make this difficult to see so don’t shine a flash light on it while doing this test.
If you have spark to your plugs then the plugs could be a problem or its more likely that you have a fuel problem.
If you don’t have spark at the plug it could be a spark plug wire or it could be dirty contacts in your distributor or it could be power not getting to your distributor coil.
Take a 12 volt test light and check that power is getting to the coil. If you are getting power to the coil then you can open your distributor cap and see if the contacts have corrosion on them. Corrosion is the normal first problem to check but there is also a condenser in the distributor that could be the issue. We are not going to go through the steps of diagnosing a condenser or a bad coil at this time but they could be an issue. If you see your points / contacts have corrosion then clean them with a piece of sand paper gently by folding the sandpaper in half so there is grit on both sides and then closing the points on them and pulling the sandpaper through the points to remove the corrosion. It does not take much effort and do not bend your points while doing this.About a 180 grit black sandpaper will work well. Blow out the dust and replace the distributor cap and try starting your engine again.
If your engine starts then you know the problem. I would suggest you do a full tuneup on the engine’s ignition system replacing the points, cap, condenser and plug wires if necessary and then the plugs if they look worn. On the other hand you could just run the vehicle for a while and prepare to do that work in the near future. Corroded points on a vehicle that has been in service normally means it is in need of servicing and having those parts replaced.
Final Note
There are other things that can go wrong with your vehicle that won’t allow it to start such as a bad battery, damaged wiring, bad fuel, dirty air and fuel filters and damaged parts.
This how to is for basic diagnosis and repair of a system that does not have more in depth repairs needed and looks to help you diagnose the difference of a fuel vs an ignition problem.
Starting fluid is really a fast way to determine if you are getting fuel or spark. If your engine starts or attempts to run when you spray starting fluid into the carburetor or even on a fuel injected system then you know that the ignition system is working. If your engine does not run when you use starting fluid then you most likely have an ignition problem and that can be from the tip of the spark plug all the way back to a problem with the ignition switch on your dashboard or steering column.
My recommendation for every person is that when you buy a new vehicle whether it is a week old or 30 years old that the first thing you do is get a good repair manual that explains all of the systems on your vehicle. And then read through the repair manual don’t just throw it on the shelf. Take a weekend or a few nights and page through the entire manual and read and skim through it. There will be important things like how to perform oil changes and filter changes that you will always need to do and there will be things you might never need to do but if you have read about it before it happens then you know where to get the exact answer when you need it. Even if you never do any work on your car you will know what a mechanic is doing so you will know if they are treating you fairly with their diagnosis and bill.