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power cuts with heavy load

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ccacio

Member
I have a 19' fourwinns horizon with a 5.0 omc and volvo out drive. boat runs great normally but when there is a heavy load on it power seems to reduce periodically. Almost like its something electrical. I recently replaced a bad alternator and battery. Wondering if something else could be at play. Any ideas would be helpful.
 
The anti-syphon valve is usually a barbed fitting connected to the top of the fuel tank pick-up line and prevents a fuel spillage into the bilges should the line between the fuel tank and the fuel pump break. Than fitting contains a spring-loaded check valve, and if it gets totally or partially stuck the fuel flow will be either reduced or even become zero. Those valves are inexpensive to replace. This picture will give you an idea of its location

http://www.louisianasportsman.com/pics/p1206462441.jpg


This is how a new anti-syphon valve looks like. There are, of course, different models and sizes.

http://www.marineengine.com/products/accessory.php?in=2560414
 
Thanks for the info. I appreciate it. Do you think that is a distinct possibility? Only seems to lose power when I have a lot of weight on the boat or with tubers?
 
You seem to loose power when there is a higher power demand, which means the engine needs more fuel. But if the fuel supply is restricted, guess what will happen....
 
LIGHTBULB!! Sometimes I also get a slight backfire or hestitation when I lay the throttle down fast. If I bring up RPMs somewhat gradually it seems fine. Last year I replaced the fuel filter, changed plugs and wires, checked timing and cleaned carb so maybe thats it. Where do you typically find that check valve?
 
ccacio said:
LIGHTBULB!! Sometimes I also get a slight backfire or hestitation when I lay the throttle down fast. If I bring up RPMs somewhat gradually it seems fine. Last year I replaced the fuel filter, changed plugs and wires, checked timing and cleaned carb so maybe thats it. Where do you typically find that check valve?
Click to expand...

The symptoms you describe (hesitation when accelerating) also correspond to a stuck or non-operating accelerator pump.

The andti-syphon valve is located on top of the fuel tank, attached to the fuel pick-up tube.
 
To detail it a little more...

If I lay the shifter down fairly quick, engine will hiccup and die. If I bring RPMs up to about 10-1500 rpm and then hit it I can get up to a decent speed fairly quick as long as I dont have a heavy load on the boat. With heavy weight (3 *****s/1 kid and 2 kids on the tube) on the boat its very difficult to get a decent hole shot and once I get out of the hole I get hesitation at higher RPMs.

Does this help with the diagnosis?
 
I still would check the anti-syphon valve; then, your next step would be the carb strainer and the accelerator pump. You may also want to check that the idle mixture/idle speed are set correctly, and that the ignition timing (both idle and total advance) is as specified.
 
I checked the water fuel seperator, no water. A few small particles of gunk settled to the bottom of gas but nothing serious. Checked the anti-siphon valve and found a few little pine needles. I cleaned them out and the springloaded "ball bearing thing" seemed to operate freely. Perhaps this was the issue. I ran the boat and it was fine but the true test is when I have a heavy load of people.

A couple other things I noticed... 1. I really had to crank the engine quite a bit to get it started. 2. Dont know if its my gauge (my trim guage and tach seem funky once in a while) but seems like I burned gas up pretty quick. Once I refill I will know how much I really had left.
 
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