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naive question about carburetor inputs/vent

1

1999john25hp

Member
Hi all,

New to outboard repair and I have some naive questions about how carbs work. There are two gas(?) lines that connect to the carb. There is small hose that comes from the primer syringe and connect to a small nipple at the top of the carb (#26 on the image below). When the engine is running, gas squirts out of the hose when disconnected from the carb.

There's also a larger hose that connects near the bottom of the carb, and that line come directly from the fuel pump, I think. I didn't try disconnecting that one.
  1. What are each of these fuel inputs doing?
  2. Should gas be coming from the syringe primer line and into the top of the carb when the syringe is all the way in and at idle?
  3. Where is the bowl vent?
I ask, because I'm getting a film of oil on/around the carb and I think it's just getting too much fuel. I've already done the following:
  • Replaced the fuel pump diaphragm and gaskets and valves.
  • Replaced the float, needle, seat, and gaskets on the carb.
  • Adjusted to the float so that it's basically level with the carb body, but angled slightly upward (when holding the carb upside down).
  • Confirmed that the squeezing the bulb on the gas line fills the bowl and closes the needle valve (the bulb gets firm).
  • I also replaced the primer syringe.
If the fuel lines seem correct and there's not a blocked bowl vent, my next project is to check/replace the reed/leaf valves inside the intake manifold.

www.crowleymarine.com

CARBURETOR - 25R, RL - 2000 Outboard 25 J25RSSE | Crowley Marine

View parts diagrams and shop online for CARBURETOR - 25R, RL parts, 2000 Outboard 25 J25RSSE. Offering discount prices on OEM parts for over 50 years. FAST $4.95 shipping available.
www.crowleymarine.com www.crowleymarine.com

2000 Johnson 25HP J25RSSE
Screenshot 2025-07-20 at 9.44.58 AM.png
 
Last edited:
After further investigation, I've discovered that fuel is squirting out of the primer hose because it is coming from the hose coming from the intake manifold, which tees with the hose coming from the primer. So maybe the reeds? Maybe something worse?
 
Reeds are rarely an issue.---But if a seagull feather is stuck in a reed ,that might be an issue.-----Post a video of what is happening.----The manual primer pulls fuel from the carburetor float bowl.----It injects it into the carburetor throat and intake manifold via small hoses.-----How does this motor start and run----Post a video?
 
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