Mechanical Fuel Pump - Mercruiser

[Don S]

Re: Mechanical Fuel Pump - Mercruiser

Lets go back to the explantion.

this one way valve prevents fuel from syphoning out of the carb back to the tank ....... over a period of a few days if the ASV is not working you have depleted carb fuel so you have to crank for a while to get fuel back to the carb

1. The fuel WILL NOT siphon out of the carb.
2. Fuel may leak back out of the line to some extent, but the fuel in the carb will be enough to start the engine, which will refill eveything within a few seconds.
3. The fuel in the carb WILL NOT evaporate in a couple of weeks. There are no openings for it to evaporate from.
4. The only possible reason for the carb to not have fuel in it after 2 weeks, is because of a leak from the bowl of the carb.


Whatever the problem is, it's in the carb, NOT the fuel pump, antisiphon valve, lines, evaporation or anything else like that.
Maybe the accelerator pump is getting week and won't pump for the first few trys.

 

[backyard mechanic]

Re: Mechanical Fuel Pump - Mercruiser

The point you make is different by a fine detail... the terms ("parts") called anti-siphon valve or check valve is somewhat synonymous but different in its purpose.

In this case a check valve is placed in the top of the fuel tank at the pickup tube. It's purpose is to stop the flow of fuel back into the tank so that "suction" isn't lost.

An anti-siphon valve is placed in a pressure line to prevent backflow of contaminated fluids to a non contaminated source. Sound similar? They are, but purposely different even though the flow may be the same. Anti-siphon valves allow for a break in vacuum to prevent siphoning. Check valves do not.

That help?

 

[intrepidvoyager]

Re: Mechanical Fuel Pump - Mercruiser

The point you make is different by a fine detail... the terms ("parts") called anti-siphon valve or check valve is somewhat synonymous but different in its purpose.

In this case a check valve is placed in the top of the fuel tank at the pickup tube. It's purpose is to stop the flow of fuel back into the tank so that "suction" isn't lost.

An anti-siphon valve is placed in a pressure line to prevent backflow of contaminated fluids to a non contaminated source. Sound similar? They are, but purposely different even though the flow may be the same. Anti-siphon valves allow for a break in vacuum to prevent siphoning. Check valves do not.

That help?

Ok ....that's what Rinker told me ...but the part from Mohler is called an antisyphon ...... and that's what we replaced and that's what solved the problem .....BUT ...I think Don is right ...we only masked the problem which is a faulty fuel pump ...... I can't remember if the engine initially fired up and then died and then we had to crank like hell or not, and had we had a carb leak ...well the problem would still be there.

So what I think was going on prior to replacing the anti syphon was that the fuel pump was leaking fuel back to the tank thru the little check valves below the fuel pump diaphram inside the fuel pump. When we replaced the faulty check/antisyphon on the tank this stopped the leak.

But Don is right I think ....antisyphon or not the pump should have easily replenished the fuel in the bowel so the pump is suspect and is probably leaking slightly internally and is not drawing properly - that's why no instant replenishment ....... I use an old electric fuel pump to move fuel around ...... it won't draw worth ****** but once its got fuel it runs just fine.

Time for a new fuel pump me thinks.

 

[elkhunter338]

Re: Mechanical Fuel Pump - Mercruiser

I think most of us have this problem with the old carb engines, boat/car or anything. The fuel evaporated out of the carb.
My 3.0 starts great unless it sits, then it takes alittle cranking or I solved that problem by installing a outboard primer ball, I prime the carb. You can tell the priming ball fills the carb back up with fuel then she fires right up.

 

[Don S]

Re: Mechanical Fuel Pump - Mercruiser

Outboard primer bulbs should not be used on an IO engine. All the fuel lines and filters have to meet CG approval and meet fire ratings. Those primer bulbs will pass nothing.

 

[Bifflefan]

Re: Mechanical Fuel Pump - Mercruiser

Once the fuel is in the carb it cant go back down the fuel line.

You've said it and Ive said it bondo, but it just doesn't seem to sink in that the fuel can't jump up to the fuel line,

Just in case you missed it, I said it too, and first....LOL

 

[elkhunter338]

Re: Mechanical Fuel Pump - Mercruiser

Coast guard inspections do not check that. Mine got signed off with a outboard primer bulb between the spin on fuel filter on the transmon and the fuel pump. Coast Guard approved in 2007.
What is the big deal rubber fuel lines from filter to fuel pump or rubber fuel lines with a primer bulb. Outboards use these to prime the engine. My kicker motor tank located inside the boat has a primer bulb on it.
Why is this a bad idea?
I am sure they can leak, but a fuel pump or the fuel lines can leak to if something is wrong with them.

 

[Don S]

Re: Mechanical Fuel Pump - Mercruiser

Coast guard inspections do not check that. Mine got signed off with a outboard primer bulb between the spin on fuel filter on the transmon and the fuel pump. Coast Guard approved in 2007.

Doesn't make it any safer, just the CG boys missed it.

Why is this a bad idea?
I am sure they can leak, but a fuel pump or the fuel lines can leak to if something is wrong with them.

Like I said before, everything in the engine compartment of an IO has to meet certain criteria to be safe.
That includes CG standards, along with ABYC standards that the manufacturers have to go buy.
The fuel bulbs will NOT meet any fire safety standards in an engine compartment.
Here they are.
http://www.access.gpo.gov/nara/cfr/waisidx_03/33cfr183_03.html

 

[intrepidvoyager]

Re: Mechanical Fuel Pump - Mercruiser

Holy Moly Don ... I am begining to understand the "ORACLE BY THE SEA" designation !!

 

[billywhizz]

Re: Mechanical Fuel Pump - Mercruiser

Lets go back to the explantion.


4. The only possible reason for the carb to not have fuel in it after 2 weeks, is because of a leak from the bowl of the carb.


OK Don, Quite happy to take your word for it and just about grasped the theory, my engine does exactly the same, so where should i be looking for the leak from within the bowl?

 

[Don S]

Re: Mechanical Fuel Pump - Mercruiser

Best thing you could do Billy, is to start a new thread with your question, also include things like what engine and carb you have.