Fuel problem on 570 ap/s

I have a 1993 570 AP/S that runs great... some of the time. This will be a little wordy, but trying to get all the particulars out there. I run the boat spot to spot at around 3500-4000 rpms, usually after the 3rd or 4th spot where I shut off the boat for a while, it starts right up and runs for a little while as normal until it begins to cut out a little bit with classic fuel starvation symptoms. The symptoms get worse until it dies completely. Through troubleshooting I disconnected the fuel line above the pump (which I replaced last season) and cranked the ignition a few times with my thumb over the open end of the hose. This resulted in no fuel spray until I removed my thumb releasing built up pressure. seeing as how the pump is only supposed to put out 5 ish PSI, I figured this was normal. I then reconnected the fuel line and checked the carb bowl to find it dry. I adjusted the needle thinking maybe it was a sticky float and through several adjustments managed to return fuel flow well enough to get it back to the ramp running under 3500 rpms. pushing it above that saw a mild return of the fuel starvation symptoms until I cut throttle back below 3500. Thinking my problem was a sticky float or needle, I rebuilt the carb over the winter. I installed and adjusted the carb and took the boat out the first couple times this season with no issues. The last 2 trips however the problem has returned with the exact same symptoms and behavior.

Other things ive checked are 1) fuel tank vent line. 2) filter. 3) water separator. 4) debris/gunk in pickup line.

Im at my wits end and considering just completely redoing the fuel system with new lines, electric pump, carb, and pulling the tank for cleaning and inspection

Is the anti-siphon (one way fuel) valve coming off the fuel tank, working properly? Or is it clogged up?

IMO........ you've done several things out of sync........ and possibly unnecessarily.

First.... check fuel pressure as per OEM specs.

It would be good to at least check the function of the anti-siphon valve....... replace if need be.
(Gasoline Engine Anti-Siphon Valves are a USCG requirement...... so do not eliminate it)

Pull the fuel tank dip tube........ look at the screen (if so equipped) for any corosion or fuel flow restriction.
Remove the screen if you wish.... your main filter will catch any debris (of which is typically over-rated anyway)!

Fuel filter cartridge...... sounds as though you replaced this. (next time go Parker/RACOR)

Does your carburetor have a small fuel filter just inside of the fuel inlet??? If so... was it replaced???

Does your ignition coil match the ignition type??? IOW.... could you be having an Ignition issue (warm/hot ignition coil malfunction).... and not a fuel related issue???


Word to the wise:
Use the P of E..... (process of elimination) ....... doing/testing/checking only one item at a time! Do not move forward until the one item has been either verified to be OK.... or has been found to be the culprit.

When used systematically and methodically, the P of E will not let you down!





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Once you get everything running OK... Per Volvo specs, the max Wide Open throttle rpms for this engine is 4600. Assuming that you have the correct prop and the engine when running OK with normal loading of fuel, passengers and gear, can reach ( but not exceed) this RPM, the recommended cruising (continuous) RPMS for best engine life is 80% of 4600 or 3680 RPMS, MAX.

If I may..... and just to clarify Bob's "but not exceed" comment.......

The WOT RPM range is intended to give the engine the correct advantage over the forces required to spin the propeller and propell the boat forward.

If you/we are going to "error" one way or another......., be sure to "error" on the side of being under-propped (I.E., a WOT RPM that may exceed the specs)

IOW..... if you/we can exceed the WOT RPM range (but avoid operating at this RPM), you/we will never over-burden our engines.
Conversely..... if you/we cannot achieve WOT RPM, you/we will be risking over-burdening the engine at ANY RPM!!!!!


Loading our smaller boats differently from normal, can also affect WOT RPM. This is why some smaller boat owners will keep two different props on board.

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Thanks for the clarification Rick. Absolutely correct. For example, assume you can get 5000 RPM at WOT with current prop. This is OK, but your max recommended cruise (continuous) RPMS is still based on 4600 RPMs. Conversely, lets say that you can get 6000 RPMs MAX out of your engine. It would be OK to use this prop (@ 80% of 4600 RPMs) in terms of not stressing the engine, but you would not get anywhere near best performance from the boat, and exceeding the 4600 MAX RPMs at any time by over 1000 RPMs is a recipe for a different type of disaster.