1989 Seaswirl OMC Cobra 5.7 boggs down & will not rev up under load

wyoskier

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Jul 11, 2020
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Hi guys!

New member here! Greetings from Wyoming! I decided to post a new thread and ask for help since I cannot find a solution.

I have a 1989 Seaswirl Sierra Classic with a OMC 5.7 Cobra that is bogging down under load and will not rev up past 1800 or 1900 rpm. Here's what it just did today. I went out on the lake and drove for about 20 minutes on plain without a problem. Stopped for and hour, moved again and sat for a couple hours. Afterwards, I started towing people in tubes behind. We probably did it for about an hour on and off. When I towed the last 2 people, I noticed the Temp gauge being right in the middle of the green.( The temp sensor installed with the EFI system off cylinder head plug was reading about 151 degrees F - more info in the next paragraph) Then as I was trying to get to plain, it started to bog down and would not rev up even if I gave it throttle. When I tried more throttle it would really bog down & sputter and loose more RPMs. So I stopped towing people and took a break. After waiting another 30 minutes I decided to head back. Now it got even worse. I couldn't go more than 2000 rpms and after 40 minutes of getting across the lake I was moving slow at about 1700 rpms with the occasional hick-up. (described as an on/off of the throttle). It idles fine and it revs up fine when in neutral. So I am confused...

More info:
I just got done installing a Performance Fuel Injection System. I spent a lot of time installing it - about 30 hours - and making sure everything is tuned up. I took the boat for a test yesterday and it ran fine. It did not get that hot - maybe 110 degrees but I had no trouble. Timing is adjusted good ( the red marks match and it idles fine around 600 RPM according to the ALDLdroid app. Everything in the boat is new: Disitributor, cap, MSD ignition coil, Ngk spark plugs, new fuel pump, inline fuel filter before fuel pump and original water separator after fuel pump. I had to install the engine coolant sensor by removing the plug on next to cylinder 8 on top of the block. The original temp sensor is installed by cylinder 2, so I figured it should be ok.

I honestly do not think the problem is related to the EFI conversion. I had the same problem - bogg down losing power and rpm - last year after towing skiers when the carburetor was installed. And the carburetor only had day trips to the lake before it started acting up.

Thank you so much for your help.

PS: Always used ethanol free premium 91 for the last 3 years
 

alldodge

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Mar 8, 2009
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Howdy
Sounds like not enough fuel. Check your fuel pressure (don't know what it should be)
It takes no fuel to rev in neutral and needs a lot under laod

If pressure is low under load, then check the antisiphon valve and fuel filter. Could be the new filter is clogged up.

Remove the canister filter and see if its full or just partly full, the pour contents into clear container to see if there is anything but clean gas
 

wyoskier

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Joined
Jul 11, 2020
Messages
4
Howdy
Sounds like not enough fuel. Check your fuel pressure (don't know what it should be)
It takes no fuel to rev in neutral and needs a lot under laod

If pressure is low under load, then check the antisiphon valve and fuel filter. Could be the new filter is clogged up.

Remove the canister filter and see if its full or just partly full, the pour contents into clear container to see if there is anything but clean gas

Thanks for getting back.

I just find it intriguing that it runs well when it is cold and after it starts acting up. I really don't think it is fuel related. I was cruising on plane for about 20 minutes at 3500 rpm and had no issues when I just launched. Then I towed people with no issues and after that it started to act up.

Any other thoughts?
 

kenny nunez

Captain
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Jun 20, 2017
Messages
3,338
Hook up a 6 gallon outboard tank and try it out. You probably have a fuel pick up tube filter clogged up or the anti siphon valve is sticking.
 

Redrig

Master Chief Petty Officer
Joined
Oct 13, 2009
Messages
860
What's the ignition situation on the efi conversion? Cuz those symptoms sound alot like my daily driver when an ignition module is failing or about to fail
 

wyoskier

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Joined
Jul 11, 2020
Messages
4
Hook up a 6 gallon outboard tank and try it out. You probably have a fuel pick up tube filter clogged up or the anti siphon valve is sticking.

I will try it out Kenny and let you know. It's a 2 hr round trip for me to go to the lake, so it might take me a couple of days to get up there. Is there a filter inside the fuel tank before the check valve?

What is the best way to clean up the whole fuel tank. Let's say I empty it out - what do I recommend cleaning it with?
 

wyoskier

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Jul 11, 2020
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kenny nunez

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Jun 20, 2017
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There is a fine screen filter in the suction tube that looks like a funnel. Pull it out and leave it out! Aluminum anti siphon valves are bad about sticking. If yours is brass then it just needs to be removed and try blowing through it from the threaded side to check for free movement. What kind of condition is the rubber fuel hose?
 
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