Losing Throttle at 1/2 tank???

[mdrinkwater]

1986 Searay Seville Mid cabin cruiser with 4.3l OMC cobra

Got the boat last August...

Blew up the outdrive, rebuilt that...

Had major issues burning through ignition coils, plus the carb (original Rochester 2bbl) was missing tons of linkage.

Boat was super hard to start, but eventually would start, and run ok...not great, at least until the ignition coil burned out.

Over the winter, I bought:

New electronic distributor kit
Edlebrock performer intake
Holly 600cfm carb

Installed everything and a new Alternator...found out lots was wired wrong, fixed that, and also found out that the resistor had been removed from the coil wire, and probably why I was burning up coils.

Got the boat out (3 times already this season ) runs great, nice pick up, starts super easy, she can sit for 2 weeks, I drop her in the water, turn the key, she fires right up, like, first crank, no pumping the carb, no throttle, just turn the key!!

But...first trip, I had a full tank of gas, ran around in the boat, and about half tank, she got a little funky on me, like the gas stopped.

So, I thought, I better change the fuel/water separator filter...this was a long repair...I think it must have been on there for 10 years....I ended up pulling the whole assembly off, ramming a pry bar through the filter to get it off, and then cleaned up the mount, installed the new filter, and attached to the boat.

I ended up having to run a new gas line from the tank to the separator, and there is a new line from the fuel pump to the carb.

So, when the tank is full, no issues, but this last trip, I was cruising along at 3000 rpm, on plane, super nice, there were a lot of boats out, and the river got pretty choppy in the underpasses, and after going through a couple, all of a sudden, the boat just started dropping, like I was pulling of the throttle, I dropped her down to 1000 rpm, no issues, up to 2000 no issues, over 2000, she started not wanting to go.

I should add, I also installed a new shift handle, and the only issue here is getting out of gear, or going from rev to forward, or forward to rev., but I think I found that issue, the interrupt switch is not working, I can pull the handle to neutral, and eventually she will slip out of gear...but I don't believe this has to do with the above issue.

So has anyone had this issue? The boat was winterized, but not made ready for summer until I swapped out the carb and all.

I am thinking that this is a tank issue...crap in the tank maybe? The pick up is clogged? Could the mechanical fuel pump be going?

If it only happens at 1/2 a tank...and according to the specs, this is a 47 gallon tank, and I know I was at 1/2 a tank, put in 12 gallons, so the gauge is reading correct.

Oil pressure was good, temp was good, voltage good...everything looked good. Any ideas?

 

[excessiveego]

Re: Losing Throttle at 1/2 tank???

Is the tank venting properly? Never had the issue on a boat, but I had a car with a plugged tank vent and it would start to loose power after a few minutes when my tank was low.

 

[mdrinkwater]

Re: Losing Throttle at 1/2 tank???

I am assuming that the vent runs next to the filler hose, and when I fill the tank, you can feel the air coming out.

I am just wondering if with the larger 4bbl on the engine, if when I hit rough water and I am down to a 1/2 tank if the gas sloshing in the take could suck air into the lines? You know, unlike on a car, the line length is a lot shorter, and the pump is actually above the tank, I am going to try again this weekend, with a full tank, and verify I am not having the issue, and then let her run down to about 1/2 a tank and see if it comes back....maybe I just need a little more volume out of the fuel pump....

 

[excessiveego]

Re: Losing Throttle at 1/2 tank???

there would need to be alot less than a half tank for the lines to suck air.... another thing is, verify that the floats in your carb are set properly, the fuel level in the bowls being too low could cause loss of power in rough water, and it could be a coincidence that your tank is half full.

 

[mdrinkwater]

Re: Losing Throttle at 1/2 tank???

there would need to be alot less than a half tank for the lines to suck air.... another thing is, verify that the floats in your carb are set properly, the fuel level in the bowls being too low could cause loss of power in rough water, and it could be a coincidence that your tank is half full.

Good thought, but the carb is new, and the issue would happen with a full tank then, and the only time I have it is when I reach 1/2 tank.

Possible: Someone swapped a fuel tank pick up with an incorrect one?
Fuel pump is going out/overheating? (it's a mechanical pump)

 

[excessiveego]

Re: Losing Throttle at 1/2 tank???

carbs are not bolt on and go, EVERY carb needs to be adjusted, even if they claim to be bolt on, I learned that a long time ago from automotive applications. The fact that it is new would be even more reason to check the floats IMO, and it's a simple procedure to check really.

and if you suspect the pickup is too short, there should be an access cover to the top of the tank, you can pull out the pickup, use a stick to check the depth of the tank and measure both to see if the pickup reaches the bottom of the tank.