1900 SR surging at WOT - Maxum Boat Owners Club

XXXMEDICXXX · 06-21-2020, 01:58 AM

I have just recently brought my 1999 1900 SR 5.0 with a 2bl back to life after an 8 year stint in mothballs. I replaced the entire exhaust system, new Fuel filter, plugs, cap, rotor, and rebuilt the carb. The boat idles perfect, runs well through the mid range, gets up on plane, but as I try to give it full throttle it surges like it is running out of gas. no backfiring or anything smoke. as I back off, it runs fine. When I am on dry land, and try to quickly "jack the throttle" with no load, it almost stalls, if I run through the throttle slowly, it is fine. the only thing I haven't replaced on the fuel system is the pump. I am thinking accelerator pump, but honestly I am scratching my head.....any help would be greatly appreciated.

mmwjr · 06-21-2020, 02:42 AM

If you slowly accelerate without issue and the issue is only when you first try to accelerate quickly the accelerator pump is bad in the carb.

XXXMEDICXXX · 06-21-2020, 02:57 AM

It rolls through the acceleration slowly on dryland fine.... slowly, but in the water, as I approach WOT it surges... even if I am gradually increasing RPMs

XXXMEDICXXX · 06-21-2020, 03:12 AM

I am wondering if I have my choke adjusted wrong. the choke is wide open upon start up. if I close it and work the accelerator arm quickly, it doesn't stutter and want to die.....what do you think?

mmwjr · 06-21-2020, 12:51 PM

Quote:

Originally Posted by XXXMEDICXXX

It rolls through the acceleration slowly on dryland fine.... slowly, but in the water, as I approach WOT it surges... even if I am gradually increasing RPMs

Testing with no load tells you nothing. A engine not firing on all cylinders can seem fine with no load.

mmwjr · 06-21-2020, 12:53 PM

Quote:

Originally Posted by XXXMEDICXXX

I am wondering if I have my choke adjusted wrong. the choke is wide open upon start up. if I close it and work the accelerator arm quickly, it doesn't stutter and want to die.....what do you think?

Do you first pump the throttle before starting? If so that should set the coke to the closed position. Once started the choke should slowly open as its element heats up.

XXXMEDICXXX · 06-25-2020, 04:15 AM

I doesnt appear that it closes at first after pumping the throttle. Today it sill had a significant hesitation getting to WOT. I can't tell the hesitation coincides with rough water, but I don't think so. It feels fuel starved. I think I am going to change the accelerator pump tomorrow. What do you think about replacing the fuel pump?

mmwjr · 06-25-2020, 12:25 PM

If you plan to open the carb to replace the accelerator pump why not just do a complete rebuild? I have no idea if replacing the fuel pump will help unless you perform a pressure test of its output to see if it’s too low on pressure.

XXXMEDICXXX · 06-25-2020, 08:59 PM

I did a complete rebuild on the carb, but I see that there are two different accelerator pumps... blue, or black.... I installed the black.. I have a pump, and was going to do that change as well.

mmwjr · 06-25-2020, 09:39 PM

Quote:

Originally Posted by XXXMEDICXXX

I did a complete rebuild on the carb, but I see that there are two different accelerator pumps... blue, or black.... I installed the black.. I have a pump, and was going to do that change as well.

Ok, let us know if these changes make a difference.

jparsons121 · 06-27-2020, 12:09 PM

A hesitation when opening throttle quickly under load would point to the accelerator pump. Linkage should have 3 holes. You could try to riches the pump shot by moving to the outer hole. If it’s truly surging after opening, I’d suspect the float level is set wrong or the needle may be sticking.
Doing a flow/pressure test could also identify if it’s a fuel pump issue or not.
I suspect that it’s in the carb, as you just did the rebuild and it’s running fine throughout the other ranges.

XXXMEDICXXX · 06-28-2020, 12:37 AM

Well.... I went through the carb again... cleaning it out, checking float level, adjusting choke, and installing a new fuel pump. The boat ran perfect. I am tempted to put the original fuel pump back as I replaced it with Fuel Pump Factory pump not a Mercruiser part... but I hate to potentially waste a good day on the water.

mmwjr · 06-28-2020, 12:54 AM

Quote:

Originally Posted by XXXMEDICXXX

Well.... I went through the carb again... cleaning it out, checking float level, adjusting choke, and installing a new fuel pump. The boat ran perfect. I am tempted to put the original fuel pump back as I replaced it with Fuel Pump Factory pump not a Mercruiser part... but I hate to potentially waste a good day on the water.

Leave well enough alone for now and enjoy the rest of the season.