86 rude possible bad fuel or pump

I have a 1986 rude vro that I mix the gas myself. It's an ellomlcdc bubble back. The fuel pump went in august. I bought a mikuni df62-702 fuel pump and rigged it on the motor. It pumps 65 liters per hour. It's made for a 150 hp snowmobile engine. Ran great in the test tank. Took it out on the water today with 3 heavy guys and a cooler of beer. Idled good in the no wake zones. Ran like a bear at full throttle for 20 minutes straight. All seemed well. Slowed down to about 5 mph for about 15 minutes and floored it. Came back up on plane like a rocket as usual. About 1 minute later, it decelerated to almost idle by itself. Then I throttled it down, paused a few seconds and floored it again. Came back up to W.O.T. then bogged down again. Did this repeatedly. At this point I just wanted to get back to the ramp. Got it on plane and ran it @ 3/4 throttle about 25 mph. It made it the 7 mile ride back with no problem @ this speed. My fuel tank is aluminum and was between 1/2 to 1/4 full. The fuel was sitting since last august, but was stabilized. I checked the factory fuel screen and was good before I left today. I also put on a new Fuel/water seperator yesterday. I can see through the factory screen and it looks ok. I didn't take it apart yet. It seems like it is starving for gas @ W.O.T. Could my fuel be bad? Could the pump have already failed? Is something plugged up even though it worked flawlessly for the first 20 minutes?

Re: 86 rude possible bad fuel or pump

Fuel doesn't last long even with stablilizer, I'd start there. Check for excess water in the seperator from condensation.

Re: 86 rude possible bad fuel or pump

I'm going to put in a temporary tank that i know is clean with fresh fuel and try that the next chance I get.

Re: 86 rude possible bad fuel or pump

A fuel pump which does not supply enough fuel volume can cause problems like you experienced. The pump will fill the carb bowls and the engine will run full speed. When the engine consumes more fuel than the pump can supply, the bowls will drain, and the engine will slow-but usually won't stall. The pump will recover and refill the bowls and the rpms will take off again. This scenario will repeat over and over. You may not notice any problem when running the engine a slightly less than full throttle-assuming the pump can keep up at slower speeds. That engine was not designed to run with a fuel separator. Some of them can cause excess fuel vacuum. Try testing with the separator disconnected.

Re: 86 rude possible bad fuel or pump

I siphoned out the old fuel and wiped the tank clean. There wasn't a lot of contaminates in the tank. Maybe 1 or 2 particles of dirt or rust.Put 12 gals. of new fuel in. I put on a new fuel separator. I checked all of my connections for air leaks. They all passed. I inspected the factory in line membrane type filter in the engine compartment and it was spotless. I did notice a tiny bit of black particles in the fuel line that goes to the factory plastic carb manifold after the filters. Took it out for sea trials yesterday. Did the same exact thing. I had my buddy keep it at wot so I could see if the primer bulb was collapsing. It wasn't. The boat's top speed is 35mph. If I keep it at around 32 mph it runs flawlessly. If I go to wot @ 35 mph it runs for about a minute and slows down by itself until the boat almost stops and then it takes off like a rocket again without missing a beat. I'm leaning towards the pump not being able to keep up. What are my options so I don't have to keep buying the wrong pumps. I really don't want to spend $400 for the non vro pump that belongs on it. I heard that a 1983 88hp pump will bolt right on my block. I don't want to risk buying the wrong pump again. Any ideas?