1987 DT150SS - Fuel Pump(s)?

[TGFish]

Last year took the boat out on a large reservoir and had this experience: Had rebuilt all carbs and fuel pumps a couple years previous and run the boat without issue for one season. On this trip, engine started and idled wonderfully, would take off and get on plane. Approx. 8 - 10 seconds after plane off, the RPMs would drop to maybe half speed (tach is shot so I can only speculate) and GPS showed we were moving at about 35mph, whereas before we could get 55-ish mph out of it. This happened consistently - Idle, full throttle, plane off, then settle back to about mid-speed. After some frustration and having checked the fuel filter, looking for kinked fuel lines, etc., I had my son drive and when the boat settled back to reduced RPM, I laid on the back deck and started pumping the primer bulb furiously, whereas the engine suddenly went to full throttle, full speed, like nothing was wrong. As long as I was pumping, we were going like gangbusters. My logic told me one of the fuel pumps were kaput. I ordered parts, anticipating that something would be obviously wrong with one of them. Upon removal and disassembly, I cannot identify any parts that show failure. All diaphragms and gaskets intact. All check valves in place, o-rings still pliable, etc. I also checked fuel flow from the tank and made certain the vent was clear, no kinks or binding of the lines. Have not had the boat back out since the latest fuel pump rebuild, but am wondering if it could be anything else? Is there anyway the openings in the block that provide the vacuum could get jammed up with carbon or otherwise clogged? Any other avenues I should explore? Thanks in advance for any suggestions.

[Murray]

Run a portable fuel tank with fresh fuel directly into the carb where the existing fuel line feeds the engine. You mention that you checked fuel flow so this test might be redundant but might be worth running anyways to verify that your fuel flow is sufficient. At the very least it will confirm if your issue is with the tank/fuel lines or engine/carbs.

You could check the pickup screen in the bottom of the tank. Any sediment in the bottom of the fuel tank? How old is the fuel? Have you syphoned a litre of fuel and let it sit for 24 hours to see if any water separates out? What is the condition of the fuel lines internally? The fuel lines could be breaking down internally. Condition/age of fuel filter? All carburetor adjustments set to manufacturer specifications? Cylinder compression? Do you have a genuine Suzuki service manual? Would be a big help for troubleshooting.

On this forum there has been talk of reed valve issues, I can’t comment on reed valves because I know very little about them. Worth searching and seeing if that might shed some light on your issue.

Hopefully other will chime in.

[Solarman]

A couple of thoughts. You cleaned & rebuilt all carbs. Did you remove the needle valve seats, and use compressed air to blow through ALL the passages? Then did you reset all the floats to specs? If floats are set too low then the fuel bowls will run too low when at full throttle. Also, if the floats are set too high, you will get too much fuel which tends to leak into the carb throats, or the carb vent.

Yes, it is possible that the small holes behind the fuel pumps that provide pressure and vaccuum could get partially blocked-up. Usually a little carb cleaner on a q-tip will clean it fine. Don't want too much carb cleaner in the hole, as it washes needed oils from important parts.

The biggest problem I've run across, is the small clear check-valves in the fuel pumps get old and start to crack/fragment/break up, they do NOT come in the factory rebuild kits (only come with new pumps), and when they crack/break up they affect the flow of fuel, often pieces lodge on the back side of the needle valve seat, reducing the flow of fuel going into the bowl. This can prevent enough fuel in the bowl too. If the main fuel pump diaphrams are old/flimsy/worn out they may not pump a full supply of fuel, then they should be changed out. Every time the needle valve seats are removed the floats should be reset to specs.

If you are pumping the bulb, and getting full throttle, and don't have any air getting in the line preventing fuel being pulled in, I would take a closer look at those items mentioned above.

Good luck, post back on what you find out.

[TGFish]

Thanks for all the input. I'll let you know what happens on my next outing. Just some notes from the responses: I will try a portable fuel tank if the issue continues. When I got the boat from friends after it had sat for awhile, I pulled the fuel tank and had it cleaned, replaced all the fuel lines, bulb, water separator, fuel filter, etc. I did purchase a genuine shop manual (invaluable in my opinion) any follow all the specs and recommendations when rebuilding, tuning, or replacing parts. I wonder about the reed valves occasionally. I have a couple older two-stroke outboards that have the original valves and run fine. I'll check the forum and manual to see if there's any recommended life-cycle on those or tell-tale signs they age getting weak. I do know if one breaks and gets ingested by the engine, it can be a mess. When I rebuilt the carb, I soaked the parts overnight, blew out all the passages, and replaced any part I could - floats, jets, needle valves, mixture screws, etc. I feel pretty confident I had the floats set correctly, especially since it ran so good for a season after the rebuild, but obviously worth another look. When I rebuilt the pumps, I replaced gaskets, diaphragms, spring, including the clear check valves and the little rubber grommets that hold them in. Made sure I had the correct side of those discs facing out as well.

Thanks again for all the direction. As with most items on this boat, it's been a great learning experience. Will definitely post an update.

[TGFish]

Follow-Up: Went through everything fuel related except checking carb floats and still had low performance at full throttle.

Opened all the carb bowls and checked float height. One was lower than the other two. Readjusted all to specs and got all float heights to within a gnats hair of each other. Voila! Runs like a beast.

[Solarman]

Many times during DIY carb cleaning, people think "I didn't change the adjustments, they should be fine". But removing and re- installing parts (like needle valve seats) can change the float settings (compression of the gasket for one instance) and should always be checked.

I'm glad all is good. Happy boating!