Hello, I am having a problem with this carburetor on a ST-180 string trimmer. The engine starts ,runs and idles for a few minutes, then shuts off. It will not restart. The reason it will not restart is because fuel continues to run into carburetor. I can watch the fuel run in and start to rise in the carburetor throat. I can pour it out and it just refills the carburetor throat, repeatedly. Left to sit the fuel runs into cylinder and out the exhaust. I rebuilt this carb with new diaphragms gaskets and new needle seat and spring. Set the needle seat lever level with straightedge across carburetor body. Any ideas what I have done wrong with the rebuild. Should I set the needle lever lower. Where is all this fuel coming from. Any help appreciated.
Did you assemble the carb properly? Sounds like you put the diagram on then the gasket. Pump side is gasket then the diaphragm and the opposite for the other side. If the pump is too close to the lever it will cause fuel to leak past the needle.
I am confident I put the carburetor together properly. The carb kit came with the same diagram you posted. I obviously have something wrong. Runs great for 5 minutes or so, then stops, flooded. I will have to tear it apart and try setting needle lever lower. Thanks for your help.
The lever needs to be flush with the body of the carb, not the floor but the outer lip. If you didn't remove the circuit plate you might have crud below the needle so you may need to disassemble the entire carb. If you can post pictures of your assembly that could help.
I found my problem. The inlet needle seat is leaking. I did a pressure test and I can see and hear the leak. I have tried stretching the spring using two different need valves. The leak persists. Nothing I have done has changed anything.
There may be some crud in the needle seat preventing it from seating properly.What I've been doing lately to ensure a clean seat is take a Q tip & pull off all the cotton on the end,then wrap a piece of cloth around the stick & dip it in Seafoam motor treatment (for cleaning carbs) & gently clean the seat.You'll be surprise on how much stuff comes out of the seat.I'd stay away from carb cleaner as it may be too harsh & damage the seat.
For what it is worth, I finally got the HDC-70B inlet needle to seat, I saw where people were using a cotton swab and brass cleaner to clean needle seat on bowl type carburetors. It worked for them. I bought some G-Tip gun cleaning swabs, mixed up some Bar Keepers Friend cleaner with water into a paste. Trimmed the swabs to just fit seat area. Chucked the swab into drill and polished away. After eight swabs the needle now seats and holds pressure. The down side is that I bought a NOS HDC -70B on Ebay, now I have an extra carburetor I do not need.