It cranks vigorously but won't start. How do I go about troubleshooting?
So far, I've:
- Changed the battery,
- Checked all spark plugs and cap
Could it be the carburetor?
If there is air, fuel, and a well timed spark it is pretty much guaranteed to at least try to run if you've got the battery to crank it. So it's a process of taking each of the areas in turn and verifying that it is working. Here are some things you could do:
Check for fuel smell, if fuel is being delivered and the engine isn't starting it will be coming out the exhaust. You'll probably be able to smell it.
If you don't smell fuel, pull the air cleaner and try dribbling a small amount of fresh fuel or starting fluid into the carburetor, if that gets the engine to fire up – even briefly – then the problem is likely to be in the fuel delivery system. If the car has been sitting for a while it may be gummed up parts in the carburetor, if it is a new and sudden problem I'd be inclined to start by looking at the fuel filter and fuel pump. Unless you know when the fuel filter was last replaced it wouldn't be a bad idea to do that.
With the air cleaner open, you're pretty much guaranteed to have a good air supply. So if the engine started easily with it off, it would be worth looking at the filter and the air pathway to see if there is a blockage.
That leaves a spark. There are lots of possibilities here. One is that the wires are bad or installed incorrectly. Your coil could have failed, or the timing could be way off. You can probably check for a spark by pulling a plug wire and holding it close to the block as you crank. You should see a spark when the wire is close to, but not touching, the block. Be careful! The voltage is high and you can get injured both by your reaction to a shock as well as by the shock itself.
That is probably enough to help you narrow down the problem. Then you can ask a more focused problem if you don't get it sorted out.
Checklist for older non working vehicles:
All the above should be checked and adjusted, then you should be good to go. Let me know which one is missing.
for your specific vehicle and the possible carb issue you are having is the butterfly valve that is getting stuck closed the automatic choke by chance? or is it your pushpull cable bends when you press the gas and the throttle does not move. can you take a picture of the valve and upload it?