1984 Mercury 150 - Starts from Cold great, then loses RPM/Power after short WOT run

[mn808gade]

sounds like your running out of fuel on one carb.i'd say one needle/seat assy plugged with something small,or screen in one carb plugged.depends on which fuel system you have.after it sits carb refills and motor will run on all six. pull two plugs wires until you find which carb/or put timming lite into each carb till you stop seeing fuel flow.-th

[something2do]

sounds like your running out of fuel on one carb.i'd say one needle/seat assy plugged with something small,or screen in one carb plugged.depends on which fuel system you have.after it sits carb refills and motor will run on all six. pull two plugs wires until you find which carb/or put timming lite into each carb till you stop seeing fuel flow.-th

Thanks for the idea. This will be the first thing I check if the coils don't turn out to be the main problem. I received the new coils in the mail, but family stuff and work have me tied up for a while. It looks like I might be able to get them swapped out for a lake test next week.

Thanks

[89Talon18]

Im no expert but sounds like your running out of fuel. I thought I had seen in the first post that you set the floats level with the float bowl when you hold it upside down. I just cleaned and gasketed a set of wh22s a week ago and im thinking the merc manual said they are supposed to hang down 1/16"

[89Talon18]

Im no expert but sounds like your running out of fuel. I thought I had seen in the first post that you set the floats level with the float bowl when you hold it upside down. I just cleaned and gasketed a set of wh22s a week ago and im thinking the merc manual said they are supposed to hang down 1/16"

[sschefer]

I suspect it's heat related, not fuel. Run it at WOT and the second it begins to falter, shut it down and check the plugs. If one or more is wetter than all the others then trouble shoot the ignition coil and switch box. If there is no difference in wetness (either all wetter than normal or all normal) then I'd go after the stator. There is a low speed ignition coil and a high speed ignition coil in the stator. The low speed falls off around 2500-3000 RPM and the high speed takes over. If the high speed coil is failing your rpm will drop off until the low speed comes back on.

[something2do]

Well, it looks like the ignition is not likely my issue after all. I found the 2 blackest plugs and put new coils on those cylinders, but had the same results on the water.

This time out, I had my wife drive and I leaned back and pumped the priming bulb rapidly, and sure enough, the boat took off. So, the engine is not getting enough fuel for some reason.

Questions, if pumping the bulb is getting the engine going again (bearing in mind that I just rebuilt the fuel pump diaphragms a few weeks ago), then does that mean that I have a restriction ahead of the bulb or I have some fuel line collapsing somewhere? Or, does this pumping action force fuel into the float bowls and it means that I have a faulty/stuck needle/seat and need to clean the carbs?

My plan right now is to replace all my fuel lines and spin on a new racor fuel/water separator. I also plan on replacing all the fuel lines in the motor as well. I had some crappy attwood fuel line in the past that had a liner that was collapsing on me so I might have some of that somewhere else in the motor to replace.

[53w]

I had similar thing happen. I put new fuel lines on and after was starving for fuel. When I pushed barbed end of the fuel filter or primer bulb into fuel line it rolled the inside of the fuel line up and blocked the barb hole. That was a crazy too find it, drove me nuts for 2 days of trouble shooting.

[ahobbes]

Something2do,

I've solved my problem, there was a section of the fuel line (from tank to primer bulb) that was older than the next section (from primer bulb to engine/bayonet connector) and so not ethanol tolerant. The lining of this part of the fuel line was disintegrating. I was out on a boat camping trip a couple of weeks ago and my boat stalled after about ten minutes of mid-high throttle (because I had to keep it under 4500 RPM otherwise I would experience bogging around 4800 RPM, as observed on the previous 3 boating runs). I was able to restart but idle was not able to be maintained. I took the cover off and started up again then noticed fuel flowing out of the vent jet/overflow on the bottom most carburetor. My friend and I decided the float must be stuck high, blocking fuel and redirecting to the vent jet. We removed the float chamber cover and fuel hoses then blew through the fuel inlet while actuating the float levers to determine the valve was in fact closing. Upon close inspection of the levers and valve opening; I noticed a very small, semi-transparent piece of hard and flaky, plastic-like material. We reassembled the carburetor, neglected to prime the bulb then started the motor. The motor seemed to run fine, the problem was fixed in that the float was no longer sticking. Over the next 2 days, I ran the motor at mid-range throttle for a number of hours without any problems. When I got back I decided to search for the cause of my WOT bogging problem starting with the screen in my fuel pump which was surprisingly clean. The factory manual instructed me to remove the bayonet connector (fuel inlet on lower cow/body area) prior to rebuilding the fuel pump. I noticed a very similar looking debris stuck to the metal ball on the inside of the bayonet connector. I did a google image search and saw exactly what I was expecting:

http://forum.gon.com/showpost.php?p=...9&postcount=10

I removed the bayonet connector and cut off the fuel line. The inlet side of the bayonet connector was clogged with the same debris. The fuel line itself was visibly "peeling" from the inside inward just like in the above photo.

I'm in the process of replacing my fuel line, cleaning out my bayonet connector (perhaps removing it and just direct plumbing as I've seen others do) and rebuilding my fuel pump to remove the last of the disintegrating fuel line debris.

[ahobbes]

After reviewing your first post I see you already replaced the fuel line. I suggest rigging up a fuel-pressure gauge after the fuel pump, I'm not sure what fuel pressure to expect but I'm in the process of confirming from my manual. I'm working on a little monitoring system to constantly monitor and compare fuel pressure and RPM. Hope I didn't mess up your thread here, just trying to eliminate possible causes.

[Magcat 62]

I DID my carbs 3 times about togive up. it was the stupid azz plug in connector o ring desinagrating every time ide plug in pieces of rubber would contaminate whole system. took weeks to figure problem.

[Magcat 62]

attwood makes the most inferior products on the market IMO

[ahobbes]

Hmm, I saw that o-ring on mine and it looks to be in-tact. Mine is metal and seems to be of good quality but if I have to replace it in the future i'll be sure to avoid attwood.

So where is the best place to put an in-line fuel filter, or perhaps use more than one, between the primer bulb and quick-disconnect/bayonet connector, between the quick-disconnect and fuel pump and/or between the fuel pump and carburetor?