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Possible to replace the primer bulb with something else?

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ragweed70

Member
I posted this in the fuel system forum as well. Just don't know how many eyes will see it there:
I seem to have a bit of a challenge with my engine maintaining a good flow of fuel.
It's an older boat with a fuel cell in the bow. The engine is a 1976 Evinrude 70HP and has a brand new fuel pump on it. The fuel line is about 15', has a bulb up at the fuel cell, and a filter back near the engine. All connections seem quite tight. I'm usually able to prime the line, and the boat seems to run quite fine at high rpms. It's at idle and/or trolling when it seems to struggle to maintain fuel pressure. I thought that I should look for a possible solution that was electric; something that might replace the primer bulb (or supplement it) and maintain constant fuel line pressure while operating. I would appreciate anyone else experience or thoughts on this.

The rookie....
 
What size is the fuel line going between motor and tank ?---Perhaps try 3/8" line there.--There may be issues with crankcase pressure pulses that drive the fuel pump.----Motor is 45 years old.
 
Rwbutler said:
What is your fuel pressure ,and what does it drop to?
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Sorry...pressure was not likely the correct terminology. Flow is likely a better term. I do not have pressure measured numbers. My evidence is the fact that under high rpm, I have no problem maintaining fuel in the glass filter. While trolling, the fuel pump does not seem to be able to keep any amount of fuel in the filter. After a while the engine starts to sputter a bit. I reprime the line and then we're good for another 10 mins or so.
 
Good question. I think I have 3/8's in there. I'll double check that later today though. Motor was fully checked out by a boat mech a couple of months ago. He put the new pump on. His comments included excellent condition, excellent running, he replaced some fuel lines around the carbs and installed a new carb kit. Perhaps I should replace all the lines around the carbs? Although...I do not see any evidence of fuel leaking.
 
ragweed70 said:
Good question. I think I have 3/8's in there. I'll double check that later today though. Motor was fully checked out by a boat mech a couple of months ago. He put the new pump on. His comments included excellent condition, excellent running, he replaced some fuel lines around the carbs and installed a new carb kit. Perhaps I should replace all the lines around the carbs? Although...I do not see any evidence of fuel leaking.
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Run it on a other tank and hose.
 
Rwbutler said:
Run it on a other tank and hose.
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Mechanic ran it off his own portable tank and hose. I have also used a portable tank and hose in the past. In both cases it worked fine. This is part of why I believe that the length of the line might be a bit of a challenge. Last year, I removed the tank in the bow and had it flushed. I also reinstalled a new fuel line, filter, and bulb. I'm going to double check all my connections and take it out again tomorrow.
 
Yes...it acted similar before the shop visit. Since the shop visit, the motor runs smoother, idles smoother and stays running at slow idle when there is fuel present in the filter. (Prior to shop visit, it wasn't running very smooth and it had a hard time staying running at idle regardless of fuel being present.)
 
Fuel line o-rings replaced??...no restriction from the filter? As I remember, back in the day, OMC had 2 available fuel lines depending on the Models horsepower....Don't know if any of those old fuel lines are still around.
 
So I had it on the lake for a full day, trolling this week. It ran very well most of the time. I believe that the issue is most likely related to small intermittant air leaks in the line. The current fuel line is a basic 3/8's fuel line from NAPA. I cannot move the tank as it is a bow tank. Once I got home, I found that I was able to retighten a couple of the line connections. I might just look at replacing the line with something that seals a bit better.

I really appreciate all the questions and hints. You guys rock!
 
While you do of course need to check your fuel lines for leaks, the elegant and economical solution to long lines and/or multiple tanks is a Facet electric fuel pump. Think of it as like a common bulb that operates at the flick of a toggle switch...A couple guys I know have the Facet pump installed in the line downstream from the switch on two and three tank systems and they really like them....It is the same "boost" pump that is used on thousands of home built Experimental Aircraft, (which is where I used them) Very very reliable. Simple to install, and is also a full backup fuel pump if the main pump fails. These pumps come in a range of pressures. the low pressure pumps are suitable for carbureted outboards. A 2 1/2 lb pressure pump works well. The guys I know have the electric pump installed at the helm. Just hit the switch before starts. if it has been sitting for awhile. The pump makes a soft noise, then stops when the pressure is good. Just like an electric fuel bulb.

These pumps are only about 50 bucks and are much more dependable than a bulb. I bought my last one at NAPA.
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I had an old '70's boat with a similar setup and battled the same thing. New fuel lines, tight connections....I tried many things but the fuel starvation issue was still there. This was on a freshly rebuilt '79 Evinrude 140 so I know crank pressure and fuel pump were in good shape. I finally cut the fiberglass and installed a tank back by the splash well which solved the problem.

A small boost pump like Doryman suggests could be a good solution. One thing I wonder is if the fuel pump on the engine can handle pressure on the suction side? Could you install the spin on fuel filter back by the motor? The filter housing usually has 2 inlet and and 2 outlet fittings. Run the boost pump to the inlet fitting and then plumb one outlet fitting as a return to the tank. You could T into the tank vent for the return flow. The other outlet on the filter would go to the primer bulb on the motor. I can't say for certain this would work but this might be a way to keep sufficient fuel volume near the motor without putting pressure against the pulse pump.
 
doryman said:
While you do of course need to check your fuel lines for leaks, the elegant and economical solution to long lines and/or multiple tanks is a Facet electric fuel pump. Think of it as like a common bulb that operates at the flick of a toggle switch...A couple guys I know have the Facet pump installed in the line downstream from the switch on two and three tank systems and they really like them....It is the same "boost" pump that is used on thousands of home built Experimental Aircraft, (which is where I used them) Very very reliable. Simple to install, and is also a full backup fuel pump if the main pump fails. These pumps come in a range of pressures. the low pressure pumps are suitable for carbureted outboards. A 2 1/2 lb pressure pump works well. The guys I know have the electric pump installed at the helm. Just hit the switch before starts. if it has been sitting for awhile. The pump makes a soft noise, then stops when the pressure is good. Just like an electric fuel bulb.

These pumps are only about 50 bucks and are much more dependable than a bulb. I bought my last one at NAPA.
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Thanks Doryman! This is exactly why I asked the original question. I thought that there must be an idea like this one floating around out there. I'll check this out.
 
kevinj said:
I had an old '70's boat with a similar setup and battled the same thing. New fuel lines, tight connections....I tried many things but the fuel starvation issue was still there. This was on a freshly rebuilt '79 Evinrude 140 so I know crank pressure and fuel pump were in good shape. I finally cut the fiberglass and installed a tank back by the splash well which solved the problem.
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Thanks Kevin. I'm trying to avoid doing that. I'm adding a kicker this year which will likely require it's own tank at the stern. I'm hoping to avoid having two tanks back there. I appreciate you confirming that you had a similar experience. I'm likely going to look for that electric pump and see what I can do with that.
 
ragweed70 said:
.....I'm likely going to look for that electric pump and see what I can do with that.
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I tend to think using the fuel pump in conjunction with the the filter housing will work, but I've never tried it so I can't say for sure. In theory the pump should keep the filter housing fully loaded with fuel and only excess will flow back to the tank in the return line. But, it's possible the return line the the outlet to the pump might fight each other for flow. If that happens you might have to put a restrictor of some kind on the return line to keep fuel flowing toward the engine. Again, this is all a big guess.

It may be possible you can just directly send from the pump to the engine. But those pulse diaphragm pumps are designed to draw fuel with a suction action so I don't know how it would react with positive pressure against it. Obviously you can just try it and see how it works.

KJ
 
My suggestion would be to use an electric fuel pump made to be used with a carburetorated engine. It will have a low fuel pressure and is pressure regulated so it can stay on as long as the engine is running. Can be bought at any auto parts store.
 
I believe the fuel line is absorbing the fuel pump's pulses at low speed and the fuel pump is not able to suck the fuel adequately. If you replace the line with something more rigid it will fix your problem. Use the flexible rubber modestly at each end, but run copper line for as far as you can. Synthetic lines in a more rigid form will work too. The hotter the weather, the more likely you will notice the starvation. Why? That fuel hose becomes slightly softer, absorbing more pulses from the pump.
 
timguy said:
I believe the fuel line is absorbing the fuel pump's pulses at low speed and the fuel pump is not able to suck the fuel adequately. If you replace the line with something more rigid it will fix your problem. Use the flexible rubber modestly at each end, but run copper line for as far as you can. Synthetic lines in a more rigid form will work too. The hotter the weather, the more likely you will notice the starvation. Why? That fuel hose becomes slightly softer, absorbing more pulses from the pump.
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Very interesting point. Certainly easier to test a new fuel line than to test a jimmy rigged pump.
 
Nothing beyond tightening up the fittings which seems to have made a marginal improvement.
I don't have a great deal of time as work keeps me quite busy.
 
I just thought I would post a quick update. I've replaced the fuel line system (again) but this time omitted the filter (temporary) and installed a new primer bulb. All joints were air tight. Took the boat out last weekend and had similar challenges while trolling at low idle. I had to prime the line every once in a while. It did work better than before though. I'm sure I had air leaks in the other line. (PS....I'm sure you guys already know this but don't buy regular 3/8's fuel line. lol) The proper marine A1 line was much easier to keep tight.
I've done a lot of reading on installing an electric pump and I think I am going to postpone that part of the project for now.
Without air leaks...I was only priming the bulb every once in a while. Not nearly as often as before.

Thanks again for all your tips, opinions, and suggestions.
Appreciate it.
 
The primer bulb is nothing but a simple manual fuel pump.----Once carburetors are full it has done its job and does nothing when motor is running.----The fuel pump on the motor is also elegantly simple and easy to trouble shoot and repair.---$6.00 diaphragm is about the only thing that can fail.----But the motor fuel pump is DRIVEN by pressure pulses from the crankcase and there may be issues there.----What trouble shooting has been done if any ??
 
The fuel pump has been replaced and the carbs rebuilt by a Marine Mechanic. (May of this year.) He went over the full functionality of the engine and did not find any additional concerns. Do you recommend any additional trouble shooting?
At this point it appears that the low pulse rate of the engine at low idle (trolling) has challenges pulling fuel the full length of the boat. All works well at a mulitude of cruising speeds. It's just at the slow idle speed.
 
You're right. I just haven't purchased a portable tank yet. I'm on the hunt for a kicker motor. When that happens, I'll likely do the portable tank at the same time.
 
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