Bogging At Full Throttle

[NS95]

Motor: Mariner 175 Magnum EFI [OD177611]
After solving the starting issue a while back, it starts fine, gets on plane fine and will cruise at about 4K RPMs which is about 3/4 throttle. But when I push it further to full throttle the motor will bog down and make like a low growling noise, will buck and vroom..vroom..vroom and drop RPM unless I back off the throttle to about 3/4 then it jumps back up like nothing happened. First thought was its starving for something, recently changed fuel lines and diaphragm kit so any suggestions for the fix would be greatly appreciated. I read on another thread to push the key in while doing this and it seemed to have no effect unless I was looking for the wrong thing.

[JOE54]

efi has no choke/verify fuel press is not dropping at wot

[NS95]

efi has no choke/verify fuel press is not dropping at wot

All right I'll try to check it tomorrow, I'm assuming it needs to be under load as I don't think blasting it on muffs is the safest idea. Just curious what are my options if fuel pressure is fine or it dips at wot?

[EuropeanAM]

You will need to check the fuel pressure on the water, under loaded conditions (at or above the RPM's where the problem is occurring).

Steps to follow will depend on the actual pressures.

Also, when you replaced the lines... can you describe the brand, type, connections, and each item done (in brief detail)?

[NS95]

You will need to check the fuel pressure on the water, under loaded conditions (at or above the RPM's where the problem is occurring).

Steps to follow will depend on the actual pressures.

Also, when you replaced the lines... can you describe the brand, type, connections, and each item done (in brief detail)?

I used B1 SAE J1527 Low Permiation hose from tank to bulb, then A1 SAE J1527 from bulb to engine. I got some of those mini band clamps to tighten the hose down on the barbs but not so tight to where it would damage the lines.

[EuropeanAM]

I used B1 SAE J1527 Low Permiation hose from tank to bulb, then A1 SAE J1527 from bulb to engine. I got some of those mini band clamps to tighten the hose down on the barbs but not so tight to where it would damage the lines.

Better re-check those lines. Should be A1-15 from tank to bulb, and then 5/16" ID B1-15 EPA (Mercury Line) from a Mercury/Quicksilver bulb, to the engine.

Fresh fuel filter, and Pulse Fuel Pump Rebuilt, all at the same time, without starting/running or pumping primer bulb in between these items.

FUEL LINES AND PERFORMANCE PROBLEMS

[NS95]

Better re-check those lines. Should be A1-15 from tank to bulb, and then 5/16" ID B1-15 EPA (Mercury Line) from a Mercury/Quicksilver bulb, to the engine.

Fresh fuel filter, and Pulse Fuel Pump Rebuilt, all at the same time, without starting/running or pumping primer bulb in between these items.

FUEL LINES AND PERFORMANCE PROBLEMS

I replaced the filter recently when I had the start issue along with the pulse pump, are you saying I need to replace them again? Im trying to get my hands on a pressure tester so I can run trials on the fuel pressure.

[stasiuk1000]

Did you check/clean the cone fuel filter between the VST and electric fuel pump? And the "top hat" filter after the electric pump? I'm no expert, but one of those filters caused me major grief!!

[NS95]

Better re-check those lines. Should be A1-15 from tank to bulb, and then 5/16" ID B1-15 EPA (Mercury Line) from a Mercury/Quicksilver bulb, to the engine.

Fresh fuel filter, and Pulse Fuel Pump Rebuilt, all at the same time, without starting/running or pumping primer bulb in between these items.

FUEL LINES AND PERFORMANCE PROBLEMS

Is there a specific place where I need to plumb the Tee in for the tester?

[QuickBullet]

Change the Fuel Filter!

[leonreno]

Fuel pressure is tested after the fuel pump on the motor, I think there maybe a valve you can plug gauge into, but not sure.

[JOE54]

should be a scharder valve on system after the elect pump prob on top of top hat filter cover

[NS95]

The vacuum gauge I bought doesn't have the schrader connection. Im curious that since its just a schrader valve can I use a regular gauge to get the pressure from the valve? Or do I still need to use the vacuum gauge and get a schrader barb fitting? BTW I have the innova 3620

[JOE54]

be sure test under load

[EuropeanAM]

I think you're talking about checking for excessive VACUUM on the supply side of the system. That's really the only place you would "tee" in.

Fuel PRESSURE is tested at a schrader valve, located above the VST (location varied).

Traditional fuel pressure gauge capable of reading 0-60 psi will work.

NOTE: You said you replaced the filter. Did you replace ALL lines tank to bulb, new OEM Mercury bulb, New 5/16" EPA Mercury line from bulb to fuel pump, REBUILD THE PULSE FUEL PUMP, and replace the fuel filter at that time?

If you skipped ANY of those items... back up and retrace your steps.

[NS95]

I think you're talking about checking for excessive VACUUM on the supply side of the system. That's really the only place you would "tee" in.

Fuel PRESSURE is tested at a schrader valve, located above the VST (location varied).

Traditional fuel pressure gauge capable of reading 0-60 psi will work.

NOTE: You said you replaced the filter. Did you replace ALL lines tank to bulb, new OEM Mercury bulb, New 5/16" EPA Mercury line from bulb to fuel pump, REBUILD THE PULSE FUEL PUMP, and replace the fuel filter at that time?

If you skipped ANY of those items... back up and retrace your steps.

Yea thats what it is, so basically that vacuum gauge won't do me any good at this particular point in time. Yea I replaced everything with mercury/oem. I did test it out with a pen gauge and at Idle it was 34psi. Haven't had the time to take it out to test under load but should be able to shortly.

[gaboy]

the gauge is probably off. it is a 39 pd. pressure reg. and usually reads 36+ pds. at schader. determine the reg. is good, like one guy said, clean all vst filters and the fuel pres. reg. filter while you are at it. is the bulb staying primed?

[NS95]

the gauge is probably off. it is a 39 pd. pressure reg. and usually reads 36+ pds. at schader. determine the reg. is good, like one guy said, clean all vst filters and the fuel pres. reg. filter while you are at it. is the bulb staying primed?

Yea the bulb is fine, just replaced it with oem mercury a month or so ago. Ill have to hit up autozone and get the loaner gauge friday and get some more accurate numbers.

[NS95]

Got a gauge on it today.
Idle=35psi
Cruise (3/4 throttle) @3500-4kRPM=20psi
4k+(full throttle)=10-12psi
I do have a video if that helps.

[EuropeanAM]

Got a gauge on it today.
Idle=35psi
Cruise (3/4 throttle) @3500-4kRPM=20psi
4k+(full throttle)=10-12psi
I do have a video if that helps.

Problem is one of the following:

-Inadequate fuel supply in the VST
-Restricted INLET screen to fuel pump
-Weak Pump (or leaking pump outlet seal)
-Pressure Regulator Problem (least likely).

Did you get pressures at 15/30/60 seconds after shutdown (also)?