Air in Gas line

[roehrle09]

I have a 3 Hp motor for my dinghy. Is there a procedure for getting an air bubble out of the line?
I have taken the carb off and held it well below the gas tank but the air bubble will not go pass the cut-off switch. I have drained all the gas and poured it back again and the bubble reappears after a while It appears to me that the carb bulb may not fill completely with gas and eventually the air bubble gets out and stalls the engine. I replaced the normal tubing with a transparent tube so I could see why the motor keeps stalling after running for a couple days. I'm pretty confident I don't have any air leaks in the lines. If I leave the motor sit for a while enough gas gets by the bubble and the motor will run again but can't get enough gas pass the bubble to run more than a couple minutes.

 

[F_R]

Re: Air in Gas line

I have a 3 Hp motor for my dinghy. Is there a procedure for getting an air bubble out of the line?
I have taken the carb off and held it well below the gas tank but the air bubble will not go pass the cut-off switch. I have drained all the gas and poured it back again and the bubble reappears after a while It appears to me that the carb bulb may not fill completely with gas and eventually the air bubble gets out and stalls the engine. I replaced the normal tubing with a transparent tube so I could see why the motor keeps stalling after running for a couple days. I'm pretty confident I don't have any air leaks in the lines. If I leave the motor sit for a while enough gas gets by the bubble and the motor will run again but can't get enough gas pass the bubble to run more than a couple minutes.

There should be a law against putting clear lines on outboards. They let you see the air inside and worries a guy to death. It is NORMAL to have air in the line--you just can't see it. Don't ask me to explain it, just believe.

You have some other problem with the motor. Have you checked the sintered filter in the tank? Remove the line and turn on the gas and see if you get a good flow.

On the other hand, it might not be a gas problem at all. Ignition problems will fool ya. (Coils).

 

[roehrle09]

Re: Air in Gas line

This isn't air, it's a very large bubble that forms in the hose that goes directly to the carb.(about an 1.5 long) I'm sure this is the problem because if I wait a few minutes it will start right up. Also it will run for a longer time if I go very slow. I believe all these facts indicate the gas can't get by the bubble fast enough to feed the carb. Also if i run the motor at home after re-filling it runs forever. To get the motor to the club it need to put it in the trunk of my car. I'm thinking now this maybe causing the problem with the motor in a horizontal position ?? I can't keep the motor at the club where I sail and need to bring the motor home each day. At the other club I belong to I was able to keep my motor on the dinghy and went weeks before I developed a blocking bubble problem.

 

[F_R]

Re: Air in Gas line

This isn't air, it's a very large bubble that forms in the hose that goes directly to the carb.(about an 1.5 long) I'm sure this is the problem because if I wait a few minutes it will start right up. Also it will run for a longer time if I go very slow. I believe all these facts indicate the gas can't get by the bubble fast enough to feed the carb. Also if i run the motor at home after re-filling it runs forever. To get the motor to the club it need to put it in the trunk of my car. I'm thinking now this maybe causing the problem with the motor in a horizontal position ?? I can't keep the motor at the club where I sail and need to bring the motor home each day. At the other club I belong to I was able to keep my motor on the dinghy and went weeks before I developed a blocking bubble problem.

I know that what I said is hard to believe, but I stand by what I said. It is normal. The fuel apparantly flows around that bubble in a very thin sheet, would be my guess. The same question constantly comes up concerning the motors that have glass fuel filter bowls. They always run empty, full of air. But run, they do.

Have you checked the flow from that sintered filter as I suggested? That would account for your running longer at slow speeds, as compared to fast. I can't explain why it runs at home. Maybe the same reason my tooth quits hurting when I get to the dentist?

 

[roehrle09]

Re: Air in Gas line

This 3 HP motor does not have a sintered filter. It has a small screen filter in the cut-off switch before the gas goes into a small plastic bulb and then to the carb. This is all one unit.

 

[F_R]

Re: Air in Gas line

This 3 HP motor does not have a sintered filter. It has a small screen filter in the cut-off switch before the gas goes into a small plastic bulb and then to the carb. This is all one unit.

OK, you have stumped me. Want to start over with the year of the motor we are discussing here? I've serviced a bazillion 3hp motors, but that one must be a lot newer.

 

[roehrle09]

Re: Air in Gas line

The motor is a 1999 3 hp Tanaka. Doesn't have a lot of time on it because I use it mainly to get to my mooring which takes less than a minute or so to travel about 100 yrds.