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73 evinrude 18hp fuel issue

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InstaGator

Contributing Member
I have a 72 evinrude that doesn't want to run at WOT. It will surge full power then bog down, then surge and bog down. It will do it over and over. It will idle and go up to ALMOST mid throttle with no problems but after that it hesitates. I suspect its the fuel pump but for this particular motor a fuel pump is $135 and a rebuild kit is not available for it. I tried pulling the fuel line from the carb and turning it over to see if it "pulses" fuel out and it does, but it doesn't seem like it is pulsing as much as it should(I have yet to find a video showing someone doing that to see how much it should pulse out when working properly). I bought a fuel pressure gauge and hooked it to the fuel line that goes into the carb, with the plug wires pulled I turned it over and it put out between 3 and 3.5 psi. I have read they should put between 1 and 2.5 psi when running depending on the RPM, but haven't found anything on how much psi it should have when not running. Ive been working on this engine for over 4 months and I'm ready to enjoy it. Ive received great help from this forum before so this is my last stop before bringing it to a marine mechanic. Thanks y'all.
 
Try pumping the bulb when the condition occurs....fuel connector o-rings in good shape???? Try borrowing a tank and hose from another motor. Fuel filter is new???
 
Yes I have Ive rebuilt it once and cleaned it another time just to make sure. I've sprayed it out with carb cleaner and compressed air and followed a few videos to make sure
 
I did forget to mention that when the problem occurs and I squeeze the primer it will straighten itself out as long as I am priming it. The fuel tank and hose to the engine are brand new. The fuel lines on the engine have not been replaced but I do not see any leaks at all even if I prime it and squeeze the primer bulb to try to put a bit of pressure in the lines. There is no fuel filter on the engine yet. Probably a good idea so I can at least see the fuel flow in the lines to get a better idea of whats going on. How would I test the lines to see if any air is getting into them to see if maybe thats the problem?
 
How would I know for sure? Or is there not a way to know for sure? I've tried pulling the fuel pump off and priming it and I don't see any fuel leaks, it just doesn't seem like it's pushing enough fuel.
 
Last time I checked it was 112 on top cylinder and 115 on bottom cylinder, but that was when it was pull start so both pulls may not have been the same. I should check it again with the electric start to get an accurate reading.
 
Fuel pressure and compression okay. How much lift from tank to motor? Also I would still replace fuel lines on motor. Also check little tube between upper and lower crankshaft. They like to crack at fittings. If squeeze bulb helps, then it is a fuel delivery problem. Try another tank/hose maybe. Some aftermarket units are problematic, or some crap in the pickup screen. Fuel pump also needs to be checked for delivery.......how much fuel is it really pumping? Just can't count on pressure alone. You need both pressure and delivery. Try to source out another pump, they are out there for good prices. Please don't use ethanol either. It will come back to haunt you. Good luck.
 
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From tank to motor is just over a foot. There is a line that goes from the side of the top cylinder to near the front of the bottom cylinder that I am not sure what its purpose is.... In the book it says it is some type of recirculation hose?? That hose is loose on the top but not so loose that it will fall off.. Anyone know what that hose is? I can post a picture if needed. The tank is in the boat and the motor on the boat just as it would be on the water. What tube are you referring to between the upper and lower crankshaft? I am not sure I know what you're referring to, which means I probably haven't checked it. Haha. The fuel pump squirts out maybe 4-5 inches of fuel and it kind of sputters. I ordered a new fuel pump today which I'm going to regret if thats not the problem, but if its not then at least i know that wont give me problems later on. I have another tank I can clean out and use(its an old metal one that came with the boat) I do not have another hose though. I got this hose at west marine for $50 bucks so I hope its a good one. I have had one hell of a time with this motor and its even stumped "marine mechanics" so I dont feel bad about not being able to figure it out, plus its been a great learning experience for me besides being a headache. I will post an update after the fuel pump arrives and I test it out. In the mean time I will try replacing all the lines and see what happens.
 
Well I have somewhat bad news...I bought a compression gauge since I borrowed the last one I used, this time the top cylinder had about 103psi and and bottom had about 121 psi so I am a little disappointed after doing the compression test. I am not sure how the compression went down since the last time I tested it since it has always been started with the correct fuel mixture and always been started with water connected or in a lake.. Is there something I am doing wrong when testing the compression or anything that could cause the top cylinder to be so much lower than last time?(last time the top cylinder was 112psi). I ordered a new fuel pump for $150 with all gaskets and shipping which was supposed to ship Friday but I got an email saying it won't ship until mid October. Being that it is Labor Day weekend I cannot call to cancel the order. My one big question is that the fuel pump on mounted on the bottom cylinder.. Would the top cylinder having low compression affect the fuel pump on the bottom cylinder? At this point I am debating on just buying a newer motor. I was not expecting the compression to go down that much when I have barely had this thing running.
 
The top and bottom cylinders are totally separated, so one will not affect the pump operation on the other. Besides, those pumps will function on cylinders otherwise too sick to run, as long as it has something resembling a piston left in it.
 
So if the motor runs good at full speed while I am priming it, would it be a good idea to still get the new fuel pump? It will take over a month to get which is ridiculous but if it will fix the problem then I will go ahead and get it. I just didn't want to get the fuel pump and find out it wasn't the problem if the top cylinder is bad and not letting the fuel pump work properly.
 
That's insane, you can likely get a pump from Wulffe Marine in 3 days. Check them out. www.wulffemarine.com. I have a used one but you should be able to find a new one or a kit. Try eBay too. Marineengine parts right here.
 
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I checked the wulffemarine website and they didn't have it. The only thing I see on eBay is for the 9.9/15hp outboards but the fuel pump looks just like the one I have. Would that make a difference since its only 3 hp difference? I have looked everywhere and only found 2 websites that have them and they both want over $100 for the fuel pump assembly without gaskets or anything. I have yet to find a rebuild kit for it. This motor is almost impossible to find parts for anymore since most of them are no longer available. I really would like to cancel the order on the fuel pump since it will be over a month but I cannot find one anywhere else. Would the one for the 15hp on eBay work? What would the difference be? It is only $36 on eBay so I hope it would work but I also don't want to spend an additional $36 just to see if it will work.
 
In your original post you said you checked the fuel pump pressure at cranking speed, which was a good reading. But what you need to do is check the pressure at the speeds that are actually giving you trouble.
 
Seems you want to change the fuel pump anyway. That's fine. The delivery of the15hp pump, in my opinion, should be adequate for the 18 or 20. How high are you lifting the fuel? What I mean is from the boat floor to fuel pump level?
 
Mr. Kim, what are you doing giving advice at 1 in the morning? You should be sleeping! Good advice, however!
My old friend, "Farmer", now long gone, always said "nightime is for hookers and thieves", ha! Also good advice......but I'm just a night owl, I guess.
 
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Alright everyone.. I'm a bit confused... I took fdrgator's advice and decided to check the fuel pressure while it was having the issue.. I replaced all fuel lines yesterday and re-adjusted the carb to the float was slightly lower than it should be(bent down slightly). I took my daughter with me today since she wanted to come... and it ran perfect. I did keep an eye on the fuel pressure gauge and it was about 1.5 barely giving it throttle, and about 3 psi WOT. I don't know if the fuel lines were bad or the carb adjustment was just right or if my daughter was my good luck charm. WOT didn't hesitate once.... I ran it for about 3 minutes WOT with no problems and as I was getting back to the dock I thought it started to hesitate but I was also getting close to the dock so I might have let off the throttle a little without realizing it. At this point I don't know what to do. I am still debating on whether or not to cancel the order for the fuel pump and try one of the ones not specifically for this engine since they are both 1/5 of the price, but I am still not sure exactly what the problem was or still could be. The main fuel line looked like it was split between the inner and outer line(it looks like there was a small tube inside a bigger tube and they had separated), but everything else looked good. I don't know if the slight carb adjustment made the difference or if the fuel lines had a problem that I could not see, but for today it ran good. I will take it out again Wednesday to a bigger lake and let it run a little longer to put it to the test. I will post another update after I see what she does. If anyone has any opinions on what it could have been/could be, please feel free to post your opinion. I am new to this game and have learned a lot, but still have lots to learn. Thank you for all of your advice and tips.
 
That is why I like to do one thing at a time that way you have a clue what was happening. If it aint broke dont fix it. It wouldnt hurt to keep a spare fuel pump in case along with spark plugs and tools.
 
I would rather not fix it at all.........if I didn't know what I did that fixed it. Its like getting an "A" on a test when you guessed all the answers, you learned little or nothing.
 
I figures the fuel lines were so cheap to replace and I am not sure how old they are I might as well replace them so that could have been the problem. Thank you.
 
I only replaced the fuel lines and adjusted the float so I guess I could put the float back to where I had it to see if that was the problem but I will keep running it and see if it acts up again. If not then just as kimcrwb1 said "If it aint broke dont fix it". I have had a ton of help from this website and as for this specific engine, I could not find much info on it besides the answers to my posts so we can help someone else that has similar issues along the way.
 
Cancel that $150 fuel pump order and go get one from NAPA or order from here.The little square ones are about 40 bucks.All the other things will probably disappear then.
 
My problem with the fuel pumps are I cannot find one that says it will fit my engine. Most of them say they are for 9.9/15 hp engines. If I buy one that will work on a 20hp will it still work on my motor as long as it bolts up the same? The ones I've found look exactly like mine but they say they are for Evinrude 9.9 and Evinrude 15hp engines, if they will work I would be more than happy to get one of those. I will cancel the order tomorrow until I look a little further into it. Thank you.
 
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