My YF doesn't power up unless I partially close the choke.
Assuming the electrical system is working correctly then you either have a vacuum leak, or not getting enough fuel.
- Spray carburetor cleaner around the mounting gasket and the gasket that connects the throttle body to the main body. If the RPM smooths out, then you found your leak. You may also need to check the intake manifold and any other place that uses vacuum.
- Check your fuel pump. It should be about 4 lbs.
- Check your float level. Use the specification from the instruction sheet.
- Your needle could be sticking not allowing enough fuel in. You can try wiping off the viton tip with mineral spirits.
- Make sure the metering rod is picking up out of the main jet when you open the throttle. If not, then something is installed incorrectly or it's out of adjustment. See how to adjust metering rod.
- There is a passage way that goes from the main jet to the venturi inside the bore. Make sure that it is clean and clear.
- The float drop should allow the needle to drop down enough to let fuel in. Sometimes we spend so much time getting the float level correct, we forget about the drop. Remember the drop can be anything as long as it lets the needle drop down, but not so far that the needle gets cocked to one side, or falls out.