1983 Mariner 115hp Inline 6 Cylinder Surging At High RPMs

[honda460ex]

Need some help. This motor runs great at times on the top end, but has it's issues if ran there long. It will fall on it's face and then pick back up. You will be cruising fine at around 5,000rpms sometimes for a long period of time and then suddenly it drops to around 4,000rpms and hovers above or below that surging and falling on its face constantly. Seems to do it more often once the motor is warmed, but not a guarantee. It doesn't have a definite trend that it follows. This motor has the electric solenoid choke which pumps fuel directly from the bowl on carb 1 straight into a fuel rail that runs directly into the block. And when the electric choke is pressed it picks back up and runs like a champ. I even held the electric choke on solid for nearly a minute while running it wide open and it never faltered. So I know the problem doesn't lie in the fuel line leading from the tank. Even if by some way it could have, I replaced the bulb and line already. I have also changed all spark plugs and checked each one for fire. They are all good. Need some GOOD ideas. I was thinking that I may possibly have a vacuum issue from one of the three carbs. Possibly a gasket gone bad? Or a vacuum line letting air in when it really gets to sucking? Any thoughts or solutions? I have already taken all three carbs off and cleaned them once. They are sitting on the work bench now for a second time... lol.

Thanks to all for reading my book I wrote...

 

[Faztbullet]

Re: 1983 Mariner 115hp Inline 6 Cylinder Surging At High RPMs

Replace fuel line if it the grey Merc line w/red lettering. This is a fuel delivery problem from:
1) debris in high speed jet
2) weak/streched fuel pump diaphram
3) debris under a inlet needle
4) sticky inlet needle
5) damaged float hanging on guide pin in bowl

 

[firstboatbuild]

Re: 1983 Mariner 115hp Inline 6 Cylinder Surging At High RPMs

Sounds like time to rebuild the carb. Also if the rubber fuel line is older I would replace it the new fuel can wreak the lining of old fuel line and plug the lines and carb. Always use stabil with ethanol treatment every time you fill the tank not just for storing.

 

[honda460ex]

Re: 1983 Mariner 115hp Inline 6 Cylinder Surging At High RPMs

I appreciate the help and ideas and would greatly appreciate anymore feedback you may have. I am beginning to think it is the diaphragm in the fuel pump. I took the three carbs apart jets and all. Cleaned them for the second time and not a one of them had anything in them that would make me think it was debris. They all three looked extremely good. The only thing that caught my attention was carb three's float was sticking slightly, but it was sticking down more so than up which would allow more fuel. I placed carb three's float in carb one and carb one's float in carb three. They both seemed to move freely then, kinda odd. So, I am ordering new floats and gaskets for all three carbs just to be safe but of course they won't be here for a few days. I did take the boat out today and tested it. I put all new fuel lines between the carbs and new vacuum lines before I took it out. Still had the same problem and it was worse. I did switch the floats back around while out and it didn't really make a difference. Keep the motor at 3,500 or less and she seems to run fine. Get it to 4,000 and above and she runs ok for a short period but then falls off quickly starving for fuel. Hit the electric choke and she comes alive for a few seconds but even it seemed to be running out of fuel today. I know that through mercury I can't get the fuel pump assembly or diaphragm anymore. So, does anyone know if I can switch to a universal electric fuel pump? If so, does anyone have a recommendation on how many psi I should run? And lastly, could I just cap the old pump off, or should I run a line from the in to the out on it so it makes a loop? Thank you, and once again, sorry for the book...

 

[honda460ex]

Re: 1983 Mariner 115hp Inline 6 Cylinder Surging At High RPMs

Ok, I found this link here to a parts place.

http://www.marinepartsplus.com/catalog/mariner/serial/115_6_CYL/+13290

Now here is another question for anyone, I have the "old style fuel pump", which if you click on it it will tell you that you can't buy it anymore. Is the "new style fuel pump" a replacement I could use or will my block be different and not accept it?

If it will fit I think I will go back to a manual pump. From what reading I have been doing here it seems to me that electric pumps aren't very highly favored.

Thanks

 

[Maxz695]

Re: 1983 Mariner 115hp Inline 6 Cylinder Surging At High RPMs

http://cgi.ebay.com/ebaymotors/New-...7285887QQptZBoatQ5fPartsQ5fAccessoriesQ5fGear not sure but check it out and this one is different http://cgi.ebay.com/ebaymotors/New-...464180QQptZBoatQ5fPartsQ5fAccessoriesQ5fGeart

 

[honda460ex]

Re: 1983 Mariner 115hp Inline 6 Cylinder Surging At High RPMs

Thanks a ton Maxz695! The second link you showed me definitely looks to be the rebuild kit for it I need... I've been on here searching for hours for a new pump, lol, you probably didn't even have to search for five minutes... Should have been looking for the rebuild kit instead!

 

[Maxz695]

Re: 1983 Mariner 115hp Inline 6 Cylinder Surging At High RPMs

1 minute 35 seconds

 

[honda460ex]

Re: 1983 Mariner 115hp Inline 6 Cylinder Surging At High RPMs

I wanted to give an update. I did get the fuel pump rebuild kit in on Friday and rebuilt it. The pump has multiple gaskets stacked between plates. One of those plates has a vacuum line etched in it from one end to the other. The gaskets that stack on top of that plate had started collapsing and sinking into the vacuum line that was etched out. I haven't tested it yet, BUT it seems to make sense to me. The motor probably wouldn't be able to run out all the way because the pump wasn't getting enough vacuum from the motor. SO, it wouldn't be able to pull enough fuel from the tank and place it in the carbs. Especially when the motor is ran wide open. I will post up the results just as soon as I get to take it out. I also bought some Sea Foam to put in my fuel. Any idea on how many ounces per gallon I should mix for the first time? I know the can says 2oz per gallon on a 2 stroke to maintain the fuel. But I want it to clean on my tank, lines, carbon build up, everything... Ideas???

Thanks To All!

 

[dw22390]

Re: 1983 Mariner 115hp Inline 6 Cylinder Surging At High RPMs

hey there any luck? I had similar problem with same motor but i had very low power under load. Ran great in the driveway but died underload. I found out my original stator was dropping a the third leg. Come to find out it was only my voltage regulator was bad and causing this. I bought one for 26$ and it rips like new again. good luck

 

[accentphoto]

Re: 1983 Mariner 115hp Inline 6 Cylinder Surging At High RPMs

I just finished rebuilding my 1984 Mercury 90hp inline 6 fuel pump about two hours ago and hopefully it will work. Its pretty cut and dry but my problem was the two check valve assembly units. I am not sure if there is a specific test for them so I just pushed lightly on each one to see if they were opening in the direction they are supposed to and hoped they are sealing enough for their age. Sadly, I could not remove one of the screws and almost stripped it (I even used a miniature impact screw driver and it didn't work). My old diaphragm was a little stiff compared to the new one and the screen and some gunk but not bad enough to cause problems. I am not sure if you have this diagram on your motor but here it is anyways:
http://www.boats.net/parts/search/Merc2/Mercury/90 (6 CYL.)/6436123 AND UP/parts.html

 

[reynold460]

Re: 1983 Mariner 115hp Inline 6 Cylinder Surging At High RPMs

i have exact same problem also bud have replaced fuel pump ,stator, switch boxes, cleaned carbs, new needle seats in carbs ,all new fuel lines . still have same problem but still working on it will let u know how i make out im finding these intermittent problems are hard to figure out

 

[reynold460]

Re: 1983 Mariner 115hp Inline 6 Cylinder Surging At High RPMs

have recently found out if i pump the fuel bulb that it will take off if it is surging also yesterday was running on muffs and when i pumped the bulb noticed air bubbles going into fuel filter so i am sucking air somewhere