TOPIC: Fuel problem - already replaced fuel pump... HELP

Honestly, I’m trying to decide if it’s time to give up. Sorry for the long post. I am so frustrated I’m getting sad. I don’t have a lot of experience, so I thought I’d get by alright as long as I’m willing to pay my local boat mechanic what he’s worth – but even when using a good outboard mechanic this has been a nightmare. I don’t really even understand my options. For the record – I am ready to become more of a DIY person as using a good mechanic hasn’t solved my problems, so if there’s anything I can try, I’ll try it. Any help or ideas will be greatly appreciated.

The engine: 1971 Mercury 500 – Thunderbolt ignition, “red line” Merc. 50 horse.

The problem: Fuel starvation at WOT.

What’s been done so far: Replaced in line fuel filter. Mechanic replaced fuel pump diaphragm.

Lake test notes: So far, the problem still persists. When it starts to starve for fuel, if I touch the choke it does not help in any way. She dies if I touch the choke while she sputters. If I pump the bulb, it DOES help - she can maintain RPMs and continue to run at WOT as long as I’m pumping the bulb.

Mechanic says:

1) it’s definitely fuel delivery related.
2) It could be caused by a pin hole air leak anywhere in the fuel delivery system.
3) Next step is to replace my fuel line and primer bulb, then the tank and pick up tube, and if that doesn’t get it – it could still be any fuel line “under the hood”. The fuel lines under the engine wrap all look good.
4) If none of that gets it, it could be caused by bad reeds (he said hammered reed block) and the solution would basically be a complete engine rebuild which he doesn’t want to do because he’d charge me more than it would be worth when done. I guess it would be time to attempt an unqualified amateur rebuild in my basement or else just dig a big hole and bury it.
5) THEN, after ALL of that, he said one more thing to me. He said we don’t sell ‘em here, so I don’t install ‘em, but there IS such a thing as an electric fuel pump. Do NOT just go buy some Holley fuel pump intended for your car. You have to get something approved by the Coast Guard for Marine use or it could be unsafe and would be illegal.

I did a Google search and found the “Holley Red Electric Marine Fuel Pump”. Link: www.holley.com/12-801-1.asp I’m thinking it might work for me if replacing the tank and lines doesn’t get it? The specs say it can be used universally for marine applications without a regulator. I tried to explain the problem to my car tinkering buddy and showed him this electric pump. He had his concerns with safety, and will it be too much fuel and flood the carbs, etc…. I couldn’t find any examples of how this product is to be used or what it’s really for, or if anybody has used one for this reason. I did stumble across a message board post where somebody asked about fuel pressure and regulators and somebody that seemed knowledgeable about these things said “I have yet to see an outboard that NEEDED fuel pressure regulation”. So maybe that IS a viable solution?

So I guess my next steps are to: Replace the tank and all fuel lines and if that doesn’t fix it, purchase and install an electric fuel pump, f that doesn’t fix it, Rebuild or dispose of the engine.

Are there other options? Is there anything else it could be? Should I just stop? Is an electric fuel pump a viable solution?

I’m running out of money to throw at this. I feel like I’m throwing good money after bad and I’m never going to get it. I don’t know anybody around here to borrow a tank and line from. I have to go buy it and there’s more money out the window… I could sink another $300 in new fuel lines, filter, primer bulb, tank, aftermarket fuel pump, wiring harness for fuel pump, and might STILL do nothing but confirm that this 40 year old engine has hammered reeds and has reached the end of it usable life.



Redundant details: That’s about it. She starts and runs and I do not have problems at low speeds. I can run it up to WOT, it’ll pop right up on a plane, then I back off to aprox 80% throttle and I can run all day long. If I try to run at wide open (or anything past that aprox 80%) for more than about 20 seconds I’ll hear RPMs start to fall and she wants to die.

check for air/fuel leaks as recommended also there is a fuel filter in the top of each carb that may be restricting fuel flow

bad sticking carb float is a possiblity, not allowing enough fuel to a carb

take it up to WOT and have someone pump the ball to see if that helps....then while at WOT shut down and immediately read the plugs, looking for a dry/lean condition if infact this is fuel starvation

MadProps wrote:

check for air/fuel leaks as recommended

I was recomended to replace the fuel tank and fuel lines. Is there a way to check these things without just trying brand new ones?

also there is a fuel filter in the top of each carb that may be restricting fuel flow
bad sticking carb float is a possiblity, not allowing enough fuel to a carb

Did I mention that I had the mechanic do a service on this engine last year which included him servicing the carbs and that did not fix the poroblem.

I don't know if it's true, but I read online that when this is happening if touching the choke helps it to not die it's a carb issue and if pumping the primer bulb helps it's a fuel pump issue.

My mechanic had me try those two things and report back. I did and he says it's not the carbs... I don't know why.

Maybe he's not that good of a mechanic?

take it up to WOT and have someone pump the ball to see if that helps....

Did that - Yes, it helps.

then while at WOT shut down and immediately read the plugs, looking for a dry/lean condition if infact this is fuel starvation

I don't know how to "read plugs for dry / lean condition"



Thanks for trying to help.

Where are you located? Maybe there is some one in your area that can help from the fourum?

It sure sounds like a fuel / pump problem.---If operating the manual standby pump ( aka primer bulb ) keeps it running then the fuel pump is not working. Possibly a crankcase pressure problem , seals / reeds / labarynth or even scored piston problem.

---

Remove bypass covers and inspect piston and rings for a start.

stashm2 wrote:

Where are you located? Maybe there is some one in your area that can help from the fourum?

I live in Seattle and I normally like to hit Lake Sammamish. If anybody happens to be in Issaquah or nearby...

Thank you, BUT, Please understand - I'm using a mechanic because I do not have mechanical skills and this whole thing is way over my head... I've been dealing with a good mechanic and this has been going on for TWO YEARS now without a solution.

professor wrote:

It sure sounds like a fuel / pump problem.---If operating the manual standby pump ( aka primer bulb ) keeps it running then the fuel pump is not working. Possibly a crankcase pressure problem , seals / reeds / labarynth

Yes, the mechanic used every one of those words. He's saying this is where we are at IF it is not solved with a new fuel tank and fuel line.

ALSO - HE said might be able to use an electric fuel pump to fix the problem. Any info on that?

professor wrote:

or even scored piston problem.

---

Remove bypass covers and inspect piston and rings for a start.

Yeah - I don't know how to do that. I know that the mechain says I have good compression in all cylinders.

Other ideas we're considering include: Mounting a wake board rack on the boat and then mounting the fuel tank on top of that to gravity feed, buying a "helper monkey" who will live in my boat and it will be his full time job to pump the primer bulb while I'm on a plane...

Have you replaced the connector to pump, pump to carb and carb to carb lines? Just because they "look" good, doesn't mean they are! They will go bad from the inside out. The lining will separate from the outer hose and collapse cuasing a restriction. This is what it sounds like to me, a restriction in one of the fuel lines. One of my rules of thumb is, with engines this old, you don't know how old the lines are........I ALWAYS replace them when getting one running for the first time after a period of sitting. In your case, the E10 fuel may have compromized the innards of your fuel lines. So, it's obvious what my advice will be......replace those fuel lines!

And lets not forget the dreaded air leak at the tank and motor connectors!

Thanks for all of the help everybody, I really do appriciate it, and I'm sorry if I sound cranky in my responses (I hope I do not). This is a frustrating situation. You all have been helpful.

I WILL change all fuel lines before moving on. Here's my plan:

Replace the fuel line that runs from the tank to the motor, including primer bulb.

Lake test

If problems persist, read my shop manual and change eevry fuel line I can find.

Lake test.

If problems still persist, try a new fuel tank with pick up tube and new Mercury fuel lione conector.


Hopefully that will get it...

...BUT, I actually understand changing fuel lines and the possible problems / reasons for doing it.

what I'm REALLY trying to get at is this:

What if none of these things help???

What if it's NOT an air leak at all... because my mechanic who's been working on it says it's worth checking for air leaks, but he's afraid it's not an air leak.... he's afraid it's a problem caused by issues with the crank case pressure, something about hammered reed block condition, bad labyrinth seal, etc...

Has anybody ever heard of using an aftermarket high performance electric fuel pump as a work around (rather than a fix) for this condition?

I didn't dream up the idea - it was suggested as a possibility by the mechanic who has worked on the boat several times and only as last ditch effort before I dig a big hole and shoot it in the power head...


Of course I will exhaust all possibilities of air leaks anywhere in the fuel system before I move on - but once I've changed every airline, and IF the problem were to persist, are there any other options?

What of the electric pump idea? Does anybody know anything about the Holley Red Electric Marine fuel pumps?

What are they for? Is that idea madness, or would it work? Unsafe? Genius? Foolish?

Am I missing a better idea?

Bless your heart for hanging in there and trying to resolve the problem yourself PM, you deserve much credit for that IMO! The guys will help you get it figured out, don't give up and bury the old girl just yet.

There is a link on NGK's site about reading plugs that may help a little. Think is, most two strokes don't leave the plugs completely clean like four strokes would, since they're burning some oil mix in the gas. Maybe the guys can elaborate on what exactly to look for here;
www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp

As far as the electric fuel pump goes, it's generally considered a bad idea or at least a last resort. The problem is safety related, if there is a fire back there the pump will continue to feed the fire pumping fuel, where a mechanical pump would quit when the engine stops. Some of the Bearcat/Homelite guys do run very small Facet pumps, but you'd have to get with them on why, I know very little about those motors.

Good luck with your issue, hope you get it straightened out.

PS - Love the "helper monkey" pumping the bulb, good to see you haven't lost your sense of humor!

IF you can pump the bulb and it WILL RUN FINE AT WOT WHILE HAND PUMPING THE PRIMER BULB......I missed this test was done first read....

in that case DEFINETLY check for air leaks!

I would buy a fuel pump kit with new check valves I think there is one on Ebay now (maybe a bad check valve not holding fuel pressure) or buy or borrow another known to work fuel pump, both cheap fixes

Sounds like a good plan to me, I automatically replace every fuel line on any old motor I drag home, be it car, boat or motorcycle. Be sure you take note of how they all hook back up.

I've only replaced reeds on an Evinrude, so maybe I should shutup now, but it was not a difficult operation. Just resist the urge to play with the reeds. like sticking your finger in wet paint.

Again, I always replace old fuel lines and I've found it to be money well spent.

Since you mentioned it a few times, do NOT use the Holley electric pump! Made for high performance I/O and V-drive motors, would need to be seriously regulated, costs a lot compared to a full rebuild or replacement of your Merc pump. I will add to others suggestions by mentioning to check the crankcase to pump area for cracks/leaks. Had an Ev with an intake cover mounted fuel pump, the pipe nipple between the cover and the pump cracked, allowing an air leak. Drove me nuts before I found it! I was ready to replace what I thought was a bad pump and found the crack when I removed the pump. Twenty five cent fix.

Kerry just tickeled my gray matter

take your cowl off and run the boat to see if it runs faster with the cowl off...

at WOT there is enough pressure to create an exhaust leak that can be strong enough to asphyxiate one or more carbs that are running fine till you get to WOT

rare problem & I heard of it again last week at another board...I had the same problem 2 years ago, split the cases resealed it and regained my RPM and top end

this is why you really need to run the motor at WOT shut down and read the plugs, to see what is really happening...plugs always tell a story of some sort....I still think your issue is fuel pressure related...but something to check

ignore my last post about exhaust leaks

I keep forgetting your monkey pumped the ball and you climbed back to WOT

Thank you all once again. You’ve given me some reasonable things to try. I will not give up hope.

MadProps – Thanks for all of the information and ideas. I’m going to try a new remote fuel tank, lines, and primer bulb next. I feel like I probably should have already tried that before posting in desperation, and it’s finally occurred to me that if it doesn’t help with this problem it’s still not a bad thing to own and I’m sure I’ll use it sometime. If that doesn’t fix my problem, I’ll definitely try running with the cover off – sounds like an easy enough test and if it doesn’t fix my problem I’ll perform the spark plug check while out lake testing. (still haven’t been able to source a good helper monkey for full time bulb pumping) So, time to buy a tank and fuel line, read up on how to read spark plugs, and hit the lake to gather more information.

Re: the electric pump idea – After a good night’s sleep, I’m liking that idea less and less even as a last resort. IF I do “hit a dead end” with this motor (which I have not just yet) then the right answer would probably be to sell it cheap to somebody who wants to rebuild it. I’m not qualified to modify any engine from its original form – so I won’t. I want to take my kids boating – safety first.

Thanks again everybody – I’ll refer to this thread and keep at it. I’ll post back to either let you know I’ve solved it, or ask for more ideas if it comes to that.


Happy boating everybody!

Re: the electric pump idea – After a good night’s sleep, I’m liking that idea less and less even as a last resort.

there are a few guys that have run electric fuel pumps on inlines, because they couldnt maintain enough constant fuel pressure but they were performance motors & they must be very low PSI pumps or run a fuel pressure regulator as already discussed and thats getting expensive
not to mention the safety aspect of running electric fuel pumps...they need to wired into your safety engine kill switch (if you have one)...see where this ones going!

start with checking the easy stuff, it most likely is a simple over looked issue

MadProps wrote:

take your cowl off and run the boat to see if it runs faster with the cowl off...

Oh yes, I once had a wasp nest in the air intake tube.

Another trouble-shooting trick. Borrow another Merc tank and line and try it out. That will tell you whether you've got an issue with your existing system...