have a 92 75hp merc outboard. the problem that just started last time i was out is that the motor, when over half throttle, looses fuel pressure, the priming bulb goes soft and the motor wont run. it works fine in trolling speed or when someone is in the back priming the bulb while at full speed. im thinking mabey an air leak in the hose but not sure cause there is no fuel leakage? anyone got any ideas? im pretty knowledgeable about the mechanic side of things but this ones got me stumped.

I had a similar problem with my outboard a few years ago, after six weeks of aggravation and checking the whole fuel system and replacing parts, I happened to have the cap off the fuel tank and when I was pumping the ball I heard the air leaking inside the tank, the pickup tube was cracked. Replaced the tube and was off and running.

Good luck

Doubletake

It could be the fuel pump diafram

Thisbuds,

Sounds like your engine is starving for fuel..

2 things
Make sure you have the air intake on your gas tanks open to allow air to replace the fuel that is being consumed.
Replace gas line to motor. You may have a clog where the problem only manifests itself at higher speed ( and consumption.)

Experienced same problem several times....you have a vacumn leak somewhere....as you increase rpms....your fuel pump draws more fuel....hence creates more vacumn to meet the need....in my case it was a faulty gasket/ o-ring on the fuel filter.

b gray hit the nail on the head, have a 80 hp merc same thing pump the bulb runs fine leave it for a minute rps drop off, opened up the fuel pump sure enough the diaphram went bad, very simple to replace and the pump kit only costs about 10.00 of course that was 6 years ago couldn't be to much, need any help let me know the hole job took 1/2hr finding all my tools took longer (jk), doug

SO here is an interesting question.

I have a 9.9 Yamaha 4 kicker connected directly to the main fuel line for my 350 Merc. I have the problem with the bulb only on the 350. When I kick up the 350 it drops dramatically and often dies. I pump the bulb on the kicker and that allows the Merc to pick back up. (kicker not even running at the time)I was thinkin that I need to run a seperate fuel tank for my kicker rather than running of the 70 Gal. main tank.

Same problem or something different? Anyone else have a clue or same experience??

The problem is that the check valve in the bulb is very cheap and gravity dependent. If you want to connect both motors to the same fuel line, you need to make sure the bulbs are nearly vertical. The problem you have now is that it is just as easy for your big motor to suck fuel/air from the little motor instead of the gas tank. What I did is put in two stainless steel 1/3psi check valves in front of the engines so that I now have only one bulb to prime both engines. Works like a champ!

I have had a similar problem with my '92 200 Yamaha. I had to have my carb rebuilt. I also noticed the o-ring on the in-line fuel filter was missing. I would start by checking your in-line filter. On mine, if you take off the engine cowl and look at the filter and try starting, if there isn't a good seel, you can see air going in the filter.

try disconnecting the fuel line from the kicker next time you run the big motor and see if the bulb goes soft, neighbor has the same problem can hardly get the bulb to pressurize but doesn't seem to effect the 9.9 as far as running, if the bulb stays hard after disconnecting your sucking air from somewhere and pulling all the gas from the 9.9, check the fitting where it attaches to the kicker and make sure it's a good snug fit, then try replaceing the bulb

ET hit it on the head, if you're running two motors off of one fuel supply, you really should use quality check valves inline to each motor. I have one tank supplying a Racor filter, the filter has two outlets, I have a check valve on each outlet, and a hose going to each motor...

-N.

Try installing shut off valves on the outlet of the filter. The check valves the others are talking about are fine as long as they do not restrict the fuel flow. Ckeck our add on Washingtonlakes.com and see our specials!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Thanks for the info guys. I will try those idea out!

Scott