Carburetor drip anomaly
Posted: Tue Mar 01, 2016 5:45 pm
I used to disbelieve in ghosts.
This week I helped a friend install some speakers in his dual carb '73 bus. When he parked at my place, I smelled fuel after a few minutes. Opening the hatch, I saw a steady but small drip from the right carb throttle shaft front bushing. Speakers were put on hold while I ripped apart the carb, cleaning out the passages, ensured the gaskets were correct and sealing, blew through the needle valve with Gum-Out, and checked bowl fuel level. Nothing stood out as unusual, so I reassembled, and found the drip-drip-drip after a few seconds of shutoff. It's occasionally present at idle, and it is pronounced right after shutdown, probably due to the lack of airflow swallowing up the fuel.
https://www.youtube.com/watch?v=pDlHlD-3c7U
Startup yielding a couple seconds of dry running, then I saw a slight drip. As a reached for my screwdriver, my friend shut it down and I cussed as the screwdriver rolled down my long and steeeeep hill. Wait a tic, what is the incline limit for a bus with factory dual carbs parked facing up the hill? With confidence, I told him "Ah yes, see the problem is not you, it's me." I ASS-UMED that my checks were good and his bus would be fine when not parked at such a slant that we needed wheel chocks...
Speaker install went fine. Until I got a phone call after he got home.
"She smells like gas and dribbles fuel on flat ground doofus."
"Ok, be right over."
This time, with my tail between my legs I swapped needle valves left to right to see if the problem follow. The problem completely ceased. I was hoping the drip would follow the needle valve and we could call it a day and a six dollar bill. Or maybe the drip would stay and I would find a bad accelerator pump check-valve or something. But no. The problem is gone, and that actually bothers me. Why is the issue gone??
So the bus is on probation, until he drives it for a week and checks for drips at Every Shutdown. We're two days into dry shutdowns now, but I want to know why my diagnostic step seemed to fix the problem.
Robbie
This week I helped a friend install some speakers in his dual carb '73 bus. When he parked at my place, I smelled fuel after a few minutes. Opening the hatch, I saw a steady but small drip from the right carb throttle shaft front bushing. Speakers were put on hold while I ripped apart the carb, cleaning out the passages, ensured the gaskets were correct and sealing, blew through the needle valve with Gum-Out, and checked bowl fuel level. Nothing stood out as unusual, so I reassembled, and found the drip-drip-drip after a few seconds of shutoff. It's occasionally present at idle, and it is pronounced right after shutdown, probably due to the lack of airflow swallowing up the fuel.
https://www.youtube.com/watch?v=pDlHlD-3c7U
Startup yielding a couple seconds of dry running, then I saw a slight drip. As a reached for my screwdriver, my friend shut it down and I cussed as the screwdriver rolled down my long and steeeeep hill. Wait a tic, what is the incline limit for a bus with factory dual carbs parked facing up the hill? With confidence, I told him "Ah yes, see the problem is not you, it's me." I ASS-UMED that my checks were good and his bus would be fine when not parked at such a slant that we needed wheel chocks...
Speaker install went fine. Until I got a phone call after he got home.
"She smells like gas and dribbles fuel on flat ground doofus."
"Ok, be right over."
This time, with my tail between my legs I swapped needle valves left to right to see if the problem follow. The problem completely ceased. I was hoping the drip would follow the needle valve and we could call it a day and a six dollar bill. Or maybe the drip would stay and I would find a bad accelerator pump check-valve or something. But no. The problem is gone, and that actually bothers me. Why is the issue gone??
So the bus is on probation, until he drives it for a week and checks for drips at Every Shutdown. We're two days into dry shutdowns now, but I want to know why my diagnostic step seemed to fix the problem.
Robbie
