Blackmax fuel issue

rjcamel2355

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Apr 22, 2015
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200hp mercury black max 2.4l

Hey guys,

Took my boat out last night and cruising around the lake. When I would open it all the way up trimmed up all the way I could go 300-400yards and you could feel it start to bog down. If I reached back and pumped the bulb (while still wide open) it would pick up for a second and suck the ball flat.

If I brought it back to idle then pumped it. It would function as normal and get hard again. I could take off again and would eventually run into the same problem.

I replaced the diaphragm / rebuilt the pump a few weeks back but this issue was never resolved. All new fuel lines clean carbs.

Is this 100% a pump issue? Or could it be my fuel tank? It has an onboard 20gal tank.

Acceleration is great, top end is excellent, idle is good also.

It doesn't seem to do this with just me in the boat, or it isn't as noticeable. If I put a few more people in the boat it seems to affect it more. (I could just be crazy though)
 

alldodge

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Not an outboard guy, but sucking the bulb down is either the fuel tank pickup tube, tank vent, or restriction in the line between bulb and tank.
 

Chris1956

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AllDodge is correct. You likely have a fuel restriction upstream of the primer bulb. Open the fuel tank cap and retest. If the boat works better, the tank breather is partially or fully clogged. If the boat does not perform better, the problem is the antisiphon valve or some other restriction.
 

rjcamel2355

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This is probably a stupid question. But..... Where and what is the anti siphon valve?
 

alldodge

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The anti-siphon valve is a barbed fitting which screws into the fuel tank and then the fuel line is attached to. The valve has a ball and spring inside it and is a safety device. If the fuel line springs a leak, it will stop fuel from siphoning the tank dry into the bilge.

50-20991_2.jpg
 

rjcamel2355

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Thank you sir, I didn't know what that was called, but I know exactly where it is lol. I'll take it loose and clear it up this afternoon, and clean my tank vents and see if it changes anything.
 

rjcamel2355

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Checked the anti syphon valve, and checked the vent in the tank. All of it was clear and clean (cleaned it anyways) went and ran the boat and still have the same issue. No kinks or anything in the fuel lines, all new fuel lines, filters are clean and clear. I didn't try pumping the primer bulb on this trip out (while running), but I'm assuming the same symptoms are there... Any clue where I should start looking next? I'm going to try a plastic external tank this weekend and see if that clears it up.... if it does I guess I'll have my answer right there.. I know, I know I should have attempted that in the first place...
 

alldodge

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It's all about testing until ya find the issue. Your saving money by not throwing parts at it like so many do. If it does work off the remote tank, the next thing would be to pull the dip tube from the tank
 

rjcamel2355

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I'm thinking it's possibly the dip tube, like you said, or in the splash well there is a fitting that goes through the fiberglass, one end the tank connects to, the other end the primer bulb set up goes to. I haven't pulled that fitting and checked it out, but I did disconnect the line at the motor, and pumped the bulb, seemed like a pretty steady stream coming through it. I could be wrong, but I'm thinking there is a filter on the bottom of the dip tube? Perhaps it's partially clogged, or something of that nature. I'll do a little investigating and report back if it's still giving me fits.
 

Rjs492

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Guys off topic I have an 89 Merc 135 stator keeps burning up on my second one in three weeks help
 

rjcamel2355

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Cleaned everything from the primer bulb back to the to the tank. All of the connectors at the tank and the fuel pick up tube and screen. Nothing was dirty or clogged. Blew through it all and back into the tank. Nothing felt or seemed restricted. Checked the air vent and the connector on the tank all of it seemed clear. I could blow into the air vent side the tank would expand and when I would stop blowing the air would blow back out. If i blew into the fuel side it wouldn't expand and just blew out of the air vent side. I'm at a loss here. It seemed to do it worse than usual over the weekend. Could it be trash getting sucked up at high rpms and then dropped back down when I bring it back to idle or kill it?
 

alldodge

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I'm wondering if this boat always had a 200 on it. Reason behind my question (remember I'm not an outboard guy) is wonder if the fuel pickup tube is to small for the motor? My 502 needs a 3/8 ID fuel line, smaller motors can use 5/16

Have you tried running it straight from a gas can?
 

rjcamel2355

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That's my next step (a remote gas can). I know there are some small particles in the fuel filter I installed. But removing the tank to clean it from this boat looks impossible. I may attempt to raise one side and the front to pool everything in one corner and suck it dry with a large electric diesel pump. I've previously ran a series of fuel filters connected to an electric fuel pump and let it cycle from the tank pickup tube back into the fuel fill hole for about 4 hours. It only have 5 gallons in it at the time. I figured I had got anything that may have been in it out.

Believe all the fuel line is 5/16s on this engine from the tube to the carbs. Previously had a 150 on it.
 
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