No Performance over 2800 RPM

[cuppa]

Hello A question for all I have a F36 which has a starboard motor that out of the hole can maitain RPS's over 3000 RPM's for about1 Minuter then bogs down to 2800 RPms and lower... I initally thought this was a problem with the timing advancing and still could be but feel it is unlikely. I have upgraded mallory ignistions, and have lubed up the mechanics and it is moving freely.. I have changed fuel filters and this has not made a difference.. Fuel is clear golden color no settlement..

The wierd thing is if I Idle the motors for a minute or more I can get them up over 3100 Rpms for another 40 -60 seconds..

what does this sound like to everyone Fuel vollume issue, carb problem timing?

any help is appreciated...

[randyp]

Sounds like fuel system issue somewhere, but my experience is limited to the 318 and rust in the tank that was bogging down the engine due to buildup in the filter. How about plugs and wires, and carb(s). Last time they were changed and serviced? Last time the carb was adjusted and/or rebuilt? Thats my 2 cents, but I'm sure there are better opinions coming your way.

[prowlersfish]

sounds like a fuel issue . Check the pick up tube and the check valve at the tank

[k9th]

I agree - fuel issue. Sounds like dirt or some sort of restriction in the fuel lines. The pickup in the tank has been mentioned and is a nasty culprit.

Good luck!

[Big D]

Agree with the pick up issue. Have a vacuum test done to determine that, and a pressure test to eliminate the possibility of a failing pump.

[captainmaniac]

Remember you probably have multiple fuel filters for that engine. Typically you might find the 'water separator' kind, a pure inline cannister filter, and then there will be a paper element filter at the carburetor. Any of them can cause fuel starvation. If all are clean, you can still have a problem with float bowl or any other settings (choke, metering screws, etc) on the carburetor, even fuel pump diaphragm problems.

Start with all filters and pickup tube as others are recommending, then I would suggest taking a thorough look at the carb next. Fuel pump would probably be last on the list.

[alexander38]

If you have Quad-jet carb there's a fine mesh nylon filter in the carb it'll do just what you have going on if its clogged. And how old are your fuel pumps ? And like guys have told you check your tubes in the tanks and anti-siphon valves and vent line before you spend your money. Fuel (gas) run about $ 160.00

[cuppa]

Guys thanks for the Quick replies, what is the best was to check / test the pickup?

Alexander I do have the Quadrajet where is that screen located?...

The carbs have had no recent work and the fuel pumps are pretty old? maybe original it is a 1985...

Let me know how to test the pickup..

[alexander38]

not owning your style boat I'll let someone else tell you how to get to your pickup tubes.
But the screen in the carb is ez. where your gas line goes in to the carb you'll see to fittings, first one takes the gas line off, the 2nd one is the boss fitting for the filter, and watch it there's a spring behind some of them. (the filter) and use 2 wrenches on those fittings. Once you have it out you can clean it or replace it.

[cuppa]

hello, the screen at the carb is clean....

what about the check valve at the tank any one with ideas on how to check that... what are the common issues with the pickup everyone is talking about..

[rooferdave]

easiest way to check pickup etc is to remove your fuel line at your filter and connect a small boat fuel tank and go out for a run, if problem persists no need to mess with your main tank(s) if prob goes away at least you have narrowed it down and then we can look at pickup tube etc,

[randyp]

I'm getting a feeling.......carb needs to be serviced and or rebuilt. Not a huge deal and worth the bucks if you don't do it yourself. But go after the fuel delivery lines, including ALL filters. The water sep filters may have accumulated sundry junk if they haven't been replaced. Don't neglect the plugs - easy to replace. Same with wires. Our boat ran like a tub until I replaced wires and plugs and rebuilt the carb....of course AFTER I discovered the galvanized fuel tank was rusting from the inside out and the rust sludge was blocking the system at the pickup, and at the filters. The others here have given you good ideas, all of which are more simple and direct than mine. I would start at the carb and work your way back to the tank. If it's clear then your next step is the carb itself AFTER you've taken an look at the plugs and wires.

[cuppa]

Hello went out for a spin today and was able to figure it out it is the fuel pickup. I think it must be a coughed screen. It is not an issue of it venting properly because I opened tank fill.and if still happened. ..., i switched the motor to use the port tank and problem went away. I switched it back and fourth and it happened each time... now how do i fix the screen the local mechanic says disconnet anti siphon and knock screen off of pickup tube because. Neither. Anti siphon or screen is needed i don't know about that though what does the group think

[Big D]

Wow, anti-siphon not needed? No way, do not remove the anti-siphon permanently. It is a safety feature.

[Paul]

The anti-syphon valve is fairly easy to service. When you remove this fitting from the tank and look inside of it, from one end you'll see the ball and from the other end you'll see a spring holding the ball in place. You'll also see a ring holding the spring in place which has two notches in it which allows it to be removed with a standard screw driver. Unscrew the ring and the spring and ball should come right out for cleaning.

I experienced the same problem as you a few years back. I was running from a storm across Lake St Clair when my engine died. (single screw) I was able to restart it however it would die again over 1500 rpm. We had to limp home at 1200 rpm and got beat up by the storm. It took me a while to figure out what the problem was and of course, it was debris caught in the anty-syphon valve.

I have since installed a new tank without this valve on the main engine line. My generator line does however have an anti-syphon valve on it. I know that many will disagree with this set up and that this valve is a safety feature however I didn't feel very safe caught in a storm on the lake with my engine starved for fuel. My fuel line now consists of a 304SS pick up tube (no screen), 304SS 90° fitting on top of the tank, copper tube with double flare fittings, shut off valve, flex line to the Racor filter then steel tube to the mechanical pump. Now if anything gets sucked up by the pick up tube it will be removed by the filter, not stuck in the antisyphon valve. And yes, I do frequent inspections of the fuel system.

I cannot say that this is the way for you to go. Removing this safety feature is a decision that only you should make, or not. I can however tell you that I have not had a fuel starvation issue since.

Hope this helps.