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50 HP Mercury 4 cycle runs then stops/primer bulb empty

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RobH1954

New member
Mechanic of 30 years- Outboards a different animal, I have a 50 HP Merc Outboard EFI 4cycle that starts easy and runs good BUT started dying at RPM higher than 3000. I noticed that when it first started I would grab the primer bulb and it woulod be empty, to get back in I would either have to lower the rpm OR pump the primer bulb while my wife drives. I can run it at 2800 RPM but it runs doggy. Here is what I have tried:
1) new tank- was going to do this anyway, the old tank was 6 gallons the new one is 12 gallons.
2) new hose line set- the onl one looked ok but with fuels being what they are I thought it a keep from getting deserted thing. The boat was 2 years old when I got it and I bought it durning Covid- the guy who owned it had probably less than 10 hours on the motor- BUT from what I have seen the hose set do deteriorate quickly.
3) I put the proper end connector on the motor, this was a bass proshop bass buggy pontoon, and for sone reason they put a hose connector/tube on the fuel line held with 2 zip ties- so I looked up the proper connection and replaced it so it would have the quick disconnect.
ALL of this I did as improvement, and thought it might take care of the engine stalling. The larger tank and the fittings and new line set was pretty much needed, large tank kept me from hauling fuel, and the quick disconnect was a proper repair for a jack leg hose connection. I DID ALL THIS JUST TO MAKE IT BETTER and hoped I might take care of the problem.
When driving at around 3K RPM it will just STUTDOWN from lack of fuel. I can feel the primer bulb -it has NOTHING IN IT, I can squeeze the bulb and get it started again, and I can get the wife to drive it BUT if she goes over 3000 rpm and IM squeezing the primer bulb, the bulb never gets hard but will continue to keep running- as long as I squeeze the bulb. it seems the motor is using more fuel than it can get from the fuel tank? It did this before the NEW tank and after with no improvement.
I though the hose/primer bulb might not be operating properly- ethanol even at the lowest percentage will destroy some rubbers and compounds, so I replaced the set with a new set from the local dealer, it did not help -no difference (glad I kept the old set as backup)
the fitting on the front of the motor was no difference (just put it on to make a bad connection good).
So Tank full of gas, primed and starts easy, runs well, then open it up it dies like no gas in the tank and the primer bulb is empty.. ANY IDEAS? I thought of the fuel pump but it has to be working or else the primer wouldnt be empty?? NEW TANK- and it did this before the change, new hose set and fittings, would do this before and after,
Mercury-50 ELPT
1F51413GZ
1C606744
Bass Buggy
Scepter 12 gallon tank ( did before and after tank change)
Atwood hose and primer bulb,
I aint going down the road of parts replacing- I hope somebody can point me in the right direction
[email protected]
 
Seems like this isn't the case after what you have changed, but the fuel pump in the engine has a suction function to suck fuel from the fuel tank and the tank can be some distance away and be below the level of the fuel pump. Removing fuel from the tank makes the air area larger, but the pressure is reduced as it enlarges. At some point, a vacuum condition occurs and the fuel pump can no longer supply fuel, and the first indication of this is a collapsed bulb.

But you said that you can pump the bulb up. Well if you have a vacuum on the tank side which collapsed the bulb, how are you able to pump fuel? One possibility is that the restriction that you are experiencing is small....small enough for you to be able to run at low fuel flows, low RPMs, and as time permits, it allows enough air back into the tank/line to allow fuel to flow so that you have something available to pump the bulb.

Somewhat confusing post.
 
Does the fuel tank have a screw on top of the cap (if it's portable) or if not, do you hear the effect from vacuum when you remove the filler cap? What does the tank have for venting?
 
the tank is a secpter (both old and new) and yes I had a dozen things running through my mind while posting- I can understand the confusion, the Bulb empties itself of fuel- it doesnt collaspe ,just empties itself- when I pick it up and squeeze it there is no friction like when the bulb is primed and stiff,- its just like when you have to prime it at the beginning. when keeping it below 3k while the wife drives if I hold the bulb I can feel the fuel going through the bulb- if I try and pump it up all the way I never achieve a "hard bulb". I figure it has to be upstream so since it is a part of normal maintenance Ill replace the filters, BUT as it comes to an end for this PARTS RE-PLACER- Im figuring it is either the low pressure pump or the High Dollar one (lol). Whatever it is it isnt allowing fuel to be pulled up. Since I had this same problem with the first tank I wouldnt think it would be a take up tube ( I did inspect the old one no holes).
 
jimn said:
Does the fuel tank have a screw on top of the cap (if it's portable) or if not, do you hear the effect from vacuum when you remove the filler cap? What does the tank have for venting?
Click to expand...
the tank is venting correctly- both of them have
 
I wonder if the jerry-rigged fuel line connection could have been a prior attempt to fix the problem you're having.

Replacing all of the fuel filters should be your next step (as you mentioned). If that doesn't fix the problem then you might need to get a shop manual and perform a fuel flow or fuel pressure test, whatever's detailed in the manual.
 
RobH1954 said:
the tank is venting correctly- both of them have
Click to expand...
Do you have a valve to prevent on e tank siphoning gas from the other, or are they both connected to the main fuel line? One primer bulb? Have you inspected the fuel line routing, to make sure it's not pinched?
 
Line and hose were replaced with an Atwood-, it was bought and the one recommended by local boat dealer- you might be correct, BUT it did the same thing as the one I took off
 
jimn said:
Do you have a valve to prevent on e tank siphoning gas from the other, or are they both connected to the main fuel line? One primer bulb? Have you inspected the fuel line routing, to make sure it's not pinched?
Click to expand...
one line one tank, I kept it simple one tank, but it did it on the old one as well.
 
Hey Im wondering could it be the low pressure fuel pump? The one that feeds the high pressure fuel pump canister? Boy I hate to get into parts replacing...
 
RobH1954 said:
Mechanic of 30 years- Outboards a different animal, I have a 50 HP Merc Outboard EFI 4cycle that starts easy and runs good BUT started dying at RPM higher than 3000. I noticed that when it first started I would grab the primer bulb and it woulod be empty, to get back in I would either have to lower the rpm OR pump the primer bulb while my wife drives. I can run it at 2800 RPM but it runs doggy. Here is what I have tried:
1) new tank- was going to do this anyway, the old tank was 6 gallons the new one is 12 gallons.
2) new hose line set- the onl one looked ok but with fuels being what they are I thought it a keep from getting deserted thing. The boat was 2 years old when I got it and I bought it durning Covid- the guy who owned it had probably less than 10 hours on the motor- BUT from what I have seen the hose set do deteriorate quickly.
3) I put the proper end connector on the motor, this was a bass proshop bass buggy pontoon, and for sone reason they put a hose connector/tube on the fuel line held with 2 zip ties- so I looked up the proper connection and replaced it so it would have the quick disconnect.
ALL of this I did as improvement, and thought it might take care of the engine stalling. The larger tank and the fittings and new line set was pretty much needed, large tank kept me from hauling fuel, and the quick disconnect was a proper repair for a jack leg hose connection. I DID ALL THIS JUST TO MAKE IT BETTER and hoped I might take care of the problem.
When driving at around 3K RPM it will just STUTDOWN from lack of fuel. I can feel the primer bulb -it has NOTHING IN IT, I can squeeze the bulb and get it started again, and I can get the wife to drive it BUT if she goes over 3000 rpm and IM squeezing the primer bulb, the bulb never gets hard but will continue to keep running- as long as I squeeze the bulb. it seems the motor is using more fuel than it can get from the fuel tank? It did this before the NEW tank and after with no improvement.
I though the hose/primer bulb might not be operating properly- ethanol even at the lowest percentage will destroy some rubbers and compounds, so I replaced the set with a new set from the local dealer, it did not help -no difference (glad I kept the old set as backup)
the fitting on the front of the motor was no difference (just put it on to make a bad connection good).
So Tank full of gas, primed and starts easy, runs well, then open it up it dies like no gas in the tank and the primer bulb is empty.. ANY IDEAS? I thought of the fuel pump but it has to be working or else the primer wouldnt be empty?? NEW TANK- and it did this before the change, new hose set and fittings, would do this before and after,
Mercury-50 ELPT
1F51413GZ
1C606744
Bass Buggy
Scepter 12 gallon tank ( did before and after tank change)
Atwood hose and primer bulb,
I aint going down the road of parts replacing- I hope somebody can point me in the right direction
[email protected]
Click to expand...
DID YOU FIGURE OUT THE PROBLEM? WE HAVE THE SAME ISSUE AND HAVE TRIED EVERYTHING.
 
I am new to this forum but will share last weekends experience , my maiden voyage on an old fiberform with a old 70 hp evinrude, it wasn't enough power to get on plane however while trying to get on plane I discovered the primer bulb was collapsing , after being towed to camp and unloading ,I used the bulb to prime the engine then removed the bulb, hooking directly to tank , motor started and ran, got on plane , my thoughts are fuel pump had enough suction to collapse bulb but wasn't overcoming check valve on bulb inlet , obviously if check valve was opening bulb wouldn't collapse , I am thinking products from the P.R.C. are not quite the same specs as oem ,I won't be able to prove that theory as the old evinrude is being replaces with a 115hp mercury what the boat is reted for
 
Texasmark said:
Il semble que ce ne soit plus le cas après vos modifications, mais la pompe à carburant du moteur possède une fonction d'aspiration pour aspirer le carburant du réservoir, et ce dernier peut être éloigné et se trouver en dessous du niveau de la pompe. Retirer du carburant du réservoir agrandit la zone d'air, mais la pression diminue à mesure qu'elle s'agrandit. À un certain moment, une dépression se produit et la pompe à carburant ne peut plus fournir de carburant, ce qui se traduit par un éclatement de la poire.

Mais vous avez dit que vous pouviez gonfler la poire. Si vous avez une dépression côté réservoir qui a fait s'effondrer la poire, comment pouvez-vous pomper du carburant ? Il est possible que la restriction que vous rencontrez soit faible… suffisamment faible pour vous permettre de rouler à faible débit et à bas régime, et, si le temps le permet, de laisser suffisamment d'air dans le réservoir/la conduite pour permettre au carburant de circuler et de disposer d'un moyen de pomper la poire.

Article un peu déroutant.
Click to expand...
 
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