50 HP Mercury fuel delivery problem

[The Dude 007]

1986 50 HP Mercury outboard - Engine is experiencing a fuel delivery problem it seems. Before I tear apart the carbs I am interested in understanding something I am seeing with the primer bulb. It will never fully inflate when connect to the engine. The spring to the rubber is good. There is no obstruction between the bulb and the fuel source. I will explain my exact trouble shooting steps thus far so that I know I am being clear about what I have seen.

After checking for a plugged screen and proper ventilation and so forth I decided to remove the fuel tank connector from the hose. I then inserted that end of the hose into the fuel tank and pumped the bulb. I also had the fuel line disconnected at the filter and had the fuel that I was pumping just going into a plastic jug. The bulb was completely inflated to begin with. As I began to prime the line it would never completely inflate. (I did block off the engine side of the line for the first several pumps to create a suction so that I wasn't just pulling air in) Ultimately I could get fuel through the line but it was difficult because the bulb just wouldn't inflate much and therefor it had very little fuel in it for me to pump forward. This was puzzling because a deflating bulb seems to be caused by upstream issues according to everything I have read thus far. I tried the bulb with the arrow pointing up and all that. Because I didn't know what else to do I then removed the connector from the hose that goes to the motor. When I do this I can pass fuel through the hose just like it should work and how it always has worked for the last 5 years of me owning the boat. The bulb inflated just how I always remember it doing. This seems to tell me there is a problem with the integrity of the connection to the motor but once again everything I have read indicates that a leak or obstruction in that area (downstream) wouldn't create the symptom of the bulb collapsing. One more thing about this is that if I get the engine running after a good prime, when it begins to bog down to where it is going to die, I can keep it running for a few more seconds if I hit the choke button. I can keep it running (not strong though) if I keep choking it every time its about to quit.

A little more history is that I have also tried another hose. I bought a new one after I noticed the bulb on the original one was not inflating like normal. I noticed that one day when I was having trouble on the lake getting the thing to start and continue running. I ended up getting off the water after fiddling with the hose a bit. (disconnecting and reconnecting and also hand pumping the bulb while my son drove) It just kind of worked after that for several trips although the bulb never acted the same again. Thats why I installed the new hose. I didn't cut the ends off of that one and go through the same trouble shooting steps of course but I figure i better mention that a completely different hose had the same symptoms while operating the motor. I actually have ran the motor for a good 10-15 hours or so on the water with these this symptom as well. It just doesnt seem to want to do that anymore! I fired up the motor a few weeks ago with the water hose and muffs for the first time after winter. Little tough to start but after it did It ran great for quite a while. I finally had a good day to go fishing since then but decided i had better try it at home again first before going to the lake. This time it ran good for a few minutes but then was starving for fuel probably after what i primed it with ran out.

Replacing the female connector on the motor seems like a good logical next step but I question that only because the bulb not inflating shouldn't because by an issue on that end according to my knowledge. I'm looking forward to more knowledge from you all! Thanks

 

[merc850]

Did you replace the whole line and bulb assembly? It sounds like the (bulb) tank side check valve is leaking and causing the fuel to flow backwards when pumped.

 

[The Dude 007]

I bought a new bulb with hose and connectors already attached on both ends. I installed it and the bulb on that one also stays partially deflated just like the other one to me. while i prime and while running the motor. At the same time I don't think it could be that check valve because it worked perfectly as long as the hose wasn't connect to the motor. (connector cut off and fuel just spraying into a jug)

Seems to make the most sense to me to replace the connection point on the motor. The real question in all this I guess is my bulb should be fully inflated while running the motor, right? It always was before. Neither the new or old one will stay inflated now though while priming or running the engine. This is most likely related to why the motor seems to be starving for fuel, yeah?

I know this doesn't seem to add up but the symptoms are occurring exactly how I wrote them.

 

[The Dude 007]

Wait... Are you saying maybe when the hose is connected to the motor there is enough additional but normal resistance that it may be forcing fuel backwards differently than when I had it disconnected? (connector actually removed) I guess that is possible but it would have to be a bad valve in the new hose as well. Also when the motor is running and the pump is sucking fuel those valves should be wide open, no?

Really thanks for your help though. The weather is good for fishing here in Utah now and this is keeping me up at night!

 

[merc850]

If the bulb is working properly it should pump fuel with the connector detached and inflate after each pump, the same will happen when attached to the motor but after a few pumps it will stay hard. The check valves in the bulb open when the motor is running to let the fuel pump draw fuel thru. Did you rebuild the fuel pump? This shows the internals of the bulb

 

[The Dude 007]

I haven't made any repairs yet.I am trying to understand why the bulb is doing what it doing first. Thought maybe someone could shed some light on why it would not inflate as soon as it is connected to the engine and everything between the bulb and fuel supply is bypasses. All accept the check valve on the tank side of course. Two different bulbs are doing the same thing though so the check valve I would assume is not the problem unless I had two bad ones.

In the first set up below I also let the fuel expel into the jug before it passed through the filter. That didn't change a thing. Only when I disconnect from the motor does the bulb work as it always did before.

 

[GA_Boater]

Have you rebuilt the fuel pump and removed the check valves during the rebuild.

I would examine the check valves in the fuel pump. I had one sticking and it is almost the same symptoms.

 

[merc850]

If the rear valve leaks the backpressure in Fig. 1 will cause fuel to move backwards and weak F flow, Fig. 2 shows no resistance to F flow so fuel moves. If the connector has a flow problem the bulb would get hard and stay hard - assuming the check valves are working. There have been reports of the line being damaged internally by ethanol.

 

[The Dude 007]

I haven't done anything yet. I believe the fuel pump is in the line after this set up though. The only thing after the bulb in this set up is the connections to the motor and then the filter. I had fuel pumping into the jug right after the filet. Also did the same thing when expelling the fuel into the jug before the filter. The only factor left is the connection at the motor. I don't know much about any of this stuff though but from everything I read a collapsing bulb is always due to problems between it and the fuel source. The reason for this post is basically to ask if that is completely true or not. It sounds like from the experience you had it is not true. Bad check valve in your fuel pump caused the bulb to mostly deflate when priming or running the motor?

 

[The Dude 007]

Maybe the second hose I got had a bad check valve in the bulb as well. I might just have to try another hose

 

[merc850]

The fuel line I have on my motor sometimes won't pump (1 out of 100 times) so I just move it around until it "catches" I can hear the fuel backflowing into the tank when this happens, if the fuel pump valves are bad the motor won't draw fuel when running.

 

[The Dude 007]

Yeah the first time I had trouble in the water I fiddled with the hose a bit. Connected and reconnected a time or two and then it ran for me. I noticed around this time the bulb was not inflating much anymore so i replaced it. Same thing with new hose and bulb but the motor has been running for me. Now it don't want to any more. I figured the problem just got worse. I was about to tear the carbs down but wanted as much feedback as I could get on this problem first. Id like to have it figured out before anything else. I appreciate all the feedback.