Fuel drips out carbs when tilted

[stevejeri]

'73 1150 inline 6
If I pump the bulb tight with motor down in run position then tilt it forward for trailering, fuel runs out carbs.
Is fuel supposed to run out of the carbs when the motor is tilted forward?
Is this only on this motor or do all motors do that?

Thanks,
Steve

 

[MercFan]

Re: Fuel drips out carbs when tilted

All motors do that. No problem.

 

[stevejeri]

Re: Fuel drips out carbs when tilted

Thanks mercfan

 

[Texasmark]

Re: Fuel drips out carbs when tilted

If the float valve is in good shape and there is no pressure on the system it helps. On newer engines it is harder to detect as they have the anti-noise cover over the carbs.

A tight squeeze bulb is another thing that can contribute to it.

Just think about it, the fuel port in the venturi of the carb (that little tube sticking up in the air inlet) is connected directly to the carb's bowl which is full of gas. When you tilt the engine, you tilt the tube and gas can run out. If the above things are as I said, it forms a vacuum. For fuel to leak out, air has to replace fuel in the bowl....no fresh air, no fuel leaks out.

HTH

Mark

 

[linckeil]

Re: Fuel drips out carbs when tilted

this happened with my '73 850. the gas flowing out the carbs actually acted as a siphon and sucked fuel directly from the gas tank. it would have kept going until it emptied the tank! luckily i caught it the next morning after parking the boat and trailer. since then i disconnect the fuel line and let the motor run until the bowls run out of fuel and the motor dies. then i tilt the motor and trailer it home.

 

[Nandy]

Re: Fuel drips out carbs when tilted

this happened with my '73 850. the gas flowing out the carbs actually acted as a siphon and sucked fuel directly from the gas tank. it would have kept going until it emptied the tank! luckily i caught it the next morning after parking the boat and trailer. since then i disconnect the fuel line and let the motor run until the bowls run out of fuel and the motor dies. then i tilt the motor and trailer it home.

Linckeil, If your motor has more than one carb, and I assume it does, it is not advisable to let the motor run until it burns all the gas. More than likelly your top carb will run out of gas first. That mean that your motor might run one or two pistons without proper lubrication. I stopped doing that since I learn about it. If I want the carbs empty I put a soaking rag or paper towel under the carb then open the screw they have in the carb to empty each carb.

 

[linckeil]

Re: Fuel drips out carbs when tilted

thats an interesting point. i never heard that. i have read and have been told that running it out of fuel is suggested prior to winterizing an outboard and that many folks do it everytime the boat comes out of the water. but i can't imagine that one carb would run out of fuel significantly earlier than the other so as to cause any lubrication issues, especially at idle. but i do understand your point and certainly wouldn't want to run 2 pistons dry.

any other opinions out there on this subject?

 

[MercFan]

Re: Fuel drips out carbs when tilted

It's pretty simple once you think about it. Didn't make sense to me either.
What happens is all the carbs use the same amount of fuel.
But the fuel line holds some fuel as well. So the top carb would run dry first, while it's fuel line still holds fuel to keep the lower carbs going. Then The carb 2 will run dry, but the fuel line to carb2 still has fuel in it, though the level is not enough to feed carb2, it's enough to feed carb3 below it. By this time carb1 has been running dry for a while. I doubt the engine will be able to run on only 2 cylinders, so it'll probably stall when carb2 runs dry, but that still gives cylinder 1&2 plenty of dry time.

This example was based on a 3 carb inline 6

PS:
This is based upon a premise that fuel can gravity feed into the float bowls. I think it can, but I might be wrong

 

[Texasmark]

Re: Fuel drips out carbs when tilted

I used to run dry every time I retrieved my boat on the trailer. Never lost an engine, including a 125 John with 4 carbs. Did it for years.

Then one day I quit doing it and never lost an engine nor crudded one up (but they don't sit more than a month without being run).

One would think that there would be some residual oil on the cylinders that run out first and you usually are at idle when you run it out.

I guess I quit when the newer fuels came out with all their cleaners and all, just don't remember.

Mark

 

[Nandy]

Re: Fuel drips out carbs when tilted

I understand that the theory might be a bit questionable. I compared the risk between emptying the carbs one way or the other and decided that the screw removal was the one with less impact. I do not empty my carbs for winterization, only for service. I think im done hijacking this post!