75hp 4-stroke can't figure this one out

75hp 4-stroke. While running full throtal all of a sudden my motor slowly begins to loose speed and then starts to idle almost as if it were not running on all cylinders. Whith out doing anything after about 30 seconds of rough idle motor clears up and the way we go for another 5or6 hundred yards, then problem begins again. Changed plugs, fuel filters, cranck shaft sensor, high pressure fuel pump and still same problem. Dealer is boggeld. Even cut the fuel line and stuck it into a jerry can to eliminate fuel and sending unit. Please help and thankyou for any advice.

Re: 75hp 4-stroke can't figure this one out

Still sounds if running out of fuel, the filters you replaced, where they the small carb inlet filters? Is your warning horn working?

Re: 75hp 4-stroke can't figure this one out

yes the two filters were for the inlet and no whent this problem occurs there is no horn or beeping, therfore nothing showing up on the computer

Re: 75hp 4-stroke can't figure this one out

The filters on the carb inlets there are 4, one for each carb.

Re: 75hp 4-stroke can't figure this one out

my motor is a 2007 EFI I see only two filters inline.

Re: 75hp 4-stroke can't figure this one out

Some place in the system you have a blockage.Ethanol is messing with the hoses.Look for a soft or mushy hose.The hoses are delaminating and the inside is collapsing.
Look for that.
Then start looking in the carb/fuel pump and bypass all the old hoses.J

Re: 75hp 4-stroke can't figure this one out

Has your dealer actually done any pressure and vacuum checks of the fuel pumps in the vapor seperator tank?
Those tests could narrow it down to the low pressure or high pressure side of the fuel system.

Re: 75hp 4-stroke can't figure this one out

Like Don S posted has the fuel rail pressure be tested when it drops off? It could be float in VST tank sticking starving the injectors/fuel pump, lack of fuel supply to VST tank or fuel pressure regulator is failing. All goes back to testing pressures...

Re: 75hp 4-stroke can't figure this one out

I have a 5-year-old 60 HP 4-stroke and sometimes my engine will die off and just idle rough. I pump the primer bulb and away I go. Here's what I found -- when I changed the filter I found tiny flakes of plastic. Tracked it down to the fuel hose between the inboard tank and engine. The alcohol in the gas was eating the lining out from the inside of the fuel line. Replace the hose and primer bulb. Still had the problem and when I pulled the engine cover I could see the fuel filter bowl was empty. I replaced the snap-on connection at the engine thinking I was sucking air, still had the problem. The filter is clean. I borrowed a portable tank, hose and connector, ran with the lid off the tank to get good tank venting, still had the problem so that points to the engine fuel pump. I removed the pump, took it apart, all the gaskets and diaphram were fine. Some days I can run all over a lake and some days the engine dies from lack of fuel after 5 minutes. Some days it does it at full throttle and some days at idle. Not wanting to take my boat to a shop I put a fuel primer hose on that will reach to the back of the driver's seat. When the engine starts to die off I just reach back and pump the bulb and away I go. It's a cheap fix for an intermitten problem. I also add Star Tron to the gas to overcome the effects of the alcohol in the gas. If my problem doesn't get any worse I'll be happy to live with my solution.

Re: 75hp 4-stroke can't figure this one out

thanks for all the info. guy's. The dealer did have the boat on the water and had his guages hooked up to the fuel line. He reconizes the problem is there that is why he changed the high pressure fuel pump. but that did not fix it. He did mention the ethanol taking a tol on the hoses, and the collapsing new hose just came in yesterday but now their is to much ice on the lakes to test. Somebody mentioned that if the altanator is not charging right like say at 9 volts instead of 14 it may be telling the computer something not abling the fuel pump to deliver all the fuel. He had that problen on a new Polaris Ranger and changing the altanator fixed everything any thoughts?