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Marine Power 8.1L Surging?

Discuss maintenance, engines, pumps and related topics. Having a problem with your boat this is a good place to ask.

Re: Marine Power 8.1L Surging?

Postby Riverjohn » Wed May 08, 2019 10:57 am

Eagle1 wrote:You get a new base. They last only 42 years.

I think I would stick to the GM standard rather than cut into the Factory wiring harness. And just keep a spare. Under $19.00 on Amazon. :Drink:
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Re: Marine Power 8.1L Surging?

Postby Eagle1 » Wed May 08, 2019 2:58 pm

Any guess as to the Amp. rating of black units ?

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Re: Marine Power 8.1L Surging?

Postby NoProplem » Wed May 08, 2019 3:19 pm

30 amps
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Re: Marine Power 8.1L Surging?

Postby backpackhunter » Wed May 08, 2019 7:54 pm

I did some more playing around today and popped off the spark arrestor on the throttle body and watched the throttle plate as I went from idle to full throttle in forward and reverse. The throttle plate opens all the way in forward full throttle but in reverse full throttle it doesn't. Shouldn't it open all the way? Would this cause that coughing/surge? I can hear the little motors whining inside the throttle body too, it seemed kind of chunky in it's movements at times, not sure if that matters.

Here is a video of the throttle plates moving: https://youtu.be/ozlsozrSs1E
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Re: Marine Power 8.1L Surging?

Postby Riverjohn » Wed May 08, 2019 10:12 pm

backpackhunter wrote:I did some more playing around today and popped off the spark arrestor on the throttle body and watched the throttle plate as I went from idle to full throttle in forward and reverse. The throttle plate opens all the way in forward full throttle but in reverse full throttle it doesn't. Shouldn't it open all the way? Would this cause that coughing/surge? I can hear the little motors whining inside the throttle body too, it seemed kind of chunky in it's movements at times, not sure if that matters.

Here is a video of the throttle plates moving: https://youtu.be/ozlsozrSs1E

Is this a single lever control?
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Re: Marine Power 8.1L Surging?

Postby backpackhunter » Wed May 08, 2019 11:16 pm

Is this a single lever control?


Yes, sir. Single lever control. I've since spoke with the previous owner and he says it was setup this way so reverse full throttle wasn't possible. With the original electric reverse bucket he said full throttle reverse was possible but he since switched it to a mechanical reverse... I'm going to change the fuel filters out tomorrow (they were just done like 20 hours ago) and see if that helps. I was also told to check the potentiometer which was under the dash on the throttle linkage. Couldn't find any loose/exposed wires or any obvious issues but I don't know how to test it and cannot find testing instructions for this one anywhere. I've found lots of info for 3 terminal potentiometers but this one has like 6 terminals.

I am running out of ideas... I've contacted a few local marine shops and once I mention "jet" they don't seem to want to call me back, lol.
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Re: Marine Power 8.1L Surging?

Postby Hell Yes » Thu May 09, 2019 10:42 pm

Mine has a fuel lift pump in front of the G-force fuel pump. Unhook the outlet fuel line from the lift pump and see if it pumps a full line of fuel into a bucket. They also have a screen in them.Mine is a 2006
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Re: Marine Power 8.1L Surging?

Postby backpackhunter » Fri May 10, 2019 12:00 am

Mine has a fuel lift pump in front of the G-force fuel pump. Unhook the outlet fuel line from the lift pump and see if it pumps a full line of fuel into a bucket. They also have a screen in them.Mine is a 2006


I'll check that tomorrow, I opened up the G-Force canister today and the fuel filter was fairly clean, no debris or anything. $64 CAD for a new filter after phoning around to a few dozen parts suppliers, trying to find it local without having to wait a week for shipping from MP. It's not a very popular fuel filter. I was able to cross reference it to a Mercedes Sprinter van but the local Mercedes dealer wanted $75 and the parts were coming from Germany, 3 week eta lol. The boat is headed to Venture River Boats next week, I think I'm throwing in the towel and will just let the pros fix it.
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Re: Marine Power 8.1L Surging?

Postby Hell Yes » Fri May 10, 2019 3:23 pm

I also put a 10mic cage fuel filter in front of fuel pumps . Less expensive to change . Should not need to change the G force filter.
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Re: Marine Power 8.1L Surging?

Postby backpackhunter » Sat May 11, 2019 9:43 pm

I also put a 10mic cage fuel filter in front of fuel pumps . Less expensive to change . Should not need to change the G force filter.


That is a good idea, it won't mess with the pump pressures at all?
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Re: Marine Power 8.1L Surging?

Postby Hell Yes » Sat May 11, 2019 11:09 pm

Mine is rated for 60 GPH. At full throtle I burn 30 , what a deal.
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Re: Marine Power 8.1L Surging?

Postby backpackhunter » Sun May 12, 2019 7:45 am

Mine is rated for 60 GPH. At full throtle I burn 30 , what a deal.


What kind of filter is it?
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Re: Marine Power 8.1L Surging?

Postby Riverjohn » Sun May 12, 2019 9:36 am

I don't think it has anything to do with any of your filters. I had a starving problem with my Kodiak MPI 502. It has the low pressure vane pump and the high pressure pump. It was cutting out at sustained runs above 3500 rpm. Replaced the water separator, the high pressure filter and the high pressure pump nothing. Was going to replace the low pressure pump when Kodiak told me about the screen in the low pressure pump. Took it apart and it was full of junk. Cleaned up and that solved the problem. Mine will surge a little like your video sometimes when it is first started in cold weather. Your problem could have something to do with what ever controls cold starts?
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Re: Marine Power 8.1L Surging?

Postby GordJ » Sun May 12, 2019 9:38 am

backpackhunter wrote:
Mine has a fuel lift pump in front of the G-force fuel pump. Unhook the outlet fuel line from the lift pump and see if it pumps a full line of fuel into a bucket. They also have a screen in them.Mine is a 2006


I'll check that tomorrow, I opened up the G-Force canister today and the fuel filter was fairly clean, no debris or anything. $64 CAD for a new filter after phoning around to a few dozen parts suppliers, trying to find it local without having to wait a week for shipping from MP. It's not a very popular fuel filter. I was able to cross reference it to a Mercedes Sprinter van but the local Mercedes dealer wanted $75 and the parts were coming from Germany, 3 week eta lol. The boat is headed to Venture River Boats next week, I think I'm throwing in the towel and will just let the pros fix it.

I’d put money on Alex getting it running.
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Re: Marine Power 8.1L Surging?

Postby Hell Yes » Sun May 12, 2019 2:30 pm

It is a normal cage style with a screw on filter. make sure it filters to 10 mic. The vain pump river john mention is the lift pump and i think the same as the low pressure pump. it primes the high pressure pump. And yes again it has a screen in it.If you do not have a filter in front of the lift pump you should check the screen.
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Re: Marine Power 8.1L Surging?

Postby backpackhunter » Mon May 13, 2019 8:42 am

This is what the low pressure pump looks like

https://marineenginedepot.com/fuel-pump-low-pressure

Is the screen just in the inlet fitting or do I take the bottom off somehow?

Thank you for all the help guys, it is much appreciated.

I’d put money on Alex getting it running.


I sure hope so!!!
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Re: Marine Power 8.1L Surging?

Postby Riverjohn » Mon May 13, 2019 8:51 am

backpackhunter wrote:This is what the low pressure pump looks like

https://marineenginedepot.com/fuel-pump-low-pressure

Is the screen just in the inlet fitting or do I take the bottom off somehow?

Thank you for all the help guys, it is much appreciated.

I’d put money on Alex getting it running.


I sure hope so!!!

No. It is under that plate at the top. You remove the 3 screw/posts. Remove the gasket and it is under there. If you turn it upside down the vanes can fall out. Easy to put back in. Pretty simple pump. I still do not think this is your problem though. If this was stopping flow it would show at high rpm not low. Good luck.
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Re: Marine Power 8.1L Surging?

Postby cangim » Wed May 15, 2019 10:02 pm

Not going to help with surge, but I have found if I turn key on and wait a few seconds I get a near immediate fire up vs 2-3 seconds of crank time. Give fuel pump time to build pressure.
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Re: Marine Power 8.1L Surging?

Postby joed40 » Thu May 16, 2019 6:22 am

I have the same setup. Had a similar issue a few years back. Replaced the low pressure fuel pump and fixed the issue.. I always carry a spare low pressure pump now.
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Re: Marine Power 8.1L Surging?

Postby Hell Yes » Thu May 16, 2019 10:50 pm

Do the bucket test for flow, if it fails check the screen. If the screen is clean get the pump.
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