Still doing the same thing!

TampaBoater

Petty Officer 1st Class
Joined
Feb 23, 2012
Messages
207
A while back Iposted about my Merc Black Max 175 bogging down and shutting off at higher rpms. Took it to shop. Mechanic said motor checks out fine (compression, sparks, temp), he ran for a long while without trouble, but found a hose on the fuel pump loose. He fixed, and today I took it to the water, and as usual, ran fine from idle to 1/2 throttle.
Kick it up to 3/4 to full throttle, and it runs for about 2 minutes before starting to slow down on it's own. I bring back to idle, and keeps going fine. I really have no idea what could be causing the problem.
Any help/thoughts appreciated.
Thanks.
 

bryanwess2000

Petty Officer 1st Class
Joined
Jul 16, 2008
Messages
240
Re: Still doing the same thing!

I haven't read any of your earlier posts but sounds like a fuel supply issue. The fuel system is cheap so start there. If you have a buddy
you can borrow a known good fuel line and primer bulb start there. I would go ahead and buy a quicksilver fuel line and bulb, not a cheapo. Rebuild the fuel pump and clean and rebuild the carbs. I wouldn't keep running it full throttle with it acting like it is. It's likely leaning out
i.e. running the carbs out of fuel at WOT then when you throttle back the fuel system catches up. A lean condition is a good way to ruin
a motor. I don't want you to pop your motor. It could be something simple like a partially plugged fuel filter or bad primer bulb or leak in fuel line sucking air in when WOT. If this motors new to you thoroughly check out the fuel, electrical, and cooling system before using it.
 

aussieflash

Lieutenant Junior Grade
Joined
Feb 5, 2011
Messages
1,004
Re: Still doing the same thing!

Tag post onto original so we know what is going on.
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,544
Re: Still doing the same thing!

I had a tower that had that problem. It ran like a scalded ape but if I made a long run at WOT, (6000 rpms) after a few minutes, it would do just that. In short I slowly ran it out of gas. It had the first oil injection mechanism in the form of a tank mounted in the boat. The engines fuel pump had to suck the fuel through it and all the plumbing associated with going from the tank thru the oil canister to the engine.

I shortened my fuel line by eliminating a lot of unnecessary twists and turns and solved the problem.

I agree on the separate 3 gal fuel tank and hose; makes a nice spare which isn't a bad idea. If it runs ok on that, (be sure and open the vent) then it's a fuel delivery problem.

Silvertip or CharlieB can tell you how to check your fuel pump for proper operation. I wouldn't kit it unless you needed to and I think that if it were a fuel pump issue, you'd have it initially at the higher rpm's.

HTH,
Mark
 
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