Merc 100 fuel delivery

[hackeyfly]

OK, here is the deal. I have a Merc. 100hp 4 cyl outboard, built between 1988 and 1993, serial # OD273957. I got this engine 3rd hand, and started using it last fall. Had some problems and ended up having new reeds put in. The old ones were chipped, I saw them when the mechanic took the carbs off to clean them. Long story short, boat ran great when I picked it up after service. This spring, I had similar problems that pointed to fuel starvation, surging and the like. Replaced the primer bulb and fuel filter on the engine. Fuel will siphon readily from the supply line if the engine connector is removed. Then I found a leak in the molded hose behind the engine fuel line connector. This hose leads from the connector to the fuel pump with a tee for accelarator pump return line, and a tee for the oil injection inflow. I figured that air was getting into the line thru the hole, causing a lean condition. Replaced the line, ran a tank of fuel thru the boat with no problems. Took th boat out the next day, and the problem started again. Bulb won't stay hard, and surging. Noticed fuel leaking from the engine connector when priming and when engine is tilted up. Replaced connector. Still leaking under pressure(when squeezing bulb).Could it be sucking air at the connection, and if so, why didn't a new connector solve the problem? I've had a Mariner 30 for 5 years and never had to touch the primer bulb to start it. Any ideas? Fuel pump rebuild is next, but if I am sucking air upstream from the pump, I don't think this will help.<br /> Thanks, Pat in MD

 

[steelespike]

Re: Merc 100 fuel delivery

Pat, If you are leaking gas at connector you sure sucking air. Dont know what your merc connector is like but im guessing the part you didnt change is bad, worn bent,cracked,tearing holes in orings etc. The bulb would not normally stay hard while running but should not colapse.If it colapses the vent is plugged or there is a blockage between tank and bulb.Another place to check is the pick up tube in the tank if it sucks air could cause problems.Could be cracked,<br />loose or coroded. Sounds like you have a handle<br />on what is needed. Good luck, Spike

 

[ODDD1]

Re: Merc 100 fuel delivery

Pat, you are right in thinking all leaks before the fuel pump will suck air.....they must be fixed....dont plan on doing the pump repair later, do it now...they have had problems with failed internal check valves....make sure you get the right one, the diaphrams should match what you have in it now....

 

[hackeyfly]

Re: Merc 100 fuel delivery

Thanks for the advice, guys. I am seriously considering eliminating the quick connector at the motor and plumbing the line right to the engine(as a trial at least). I have the factory Merc. Service manual for this motor, but the 2 styles of fuel pump it shows are different than mine. The book shows the oil injection line entering the cover of the fuel pump. My oil injection line Tees into the fuel line upstream of the pump. Is there anywhere I can get service bulletins that cover changes and advisories? Also, on my last sea trial, I got surging as I crossed the wake of a large vessel. Just a little pounding, like what you get with the trim too far up. Are the carb bowls running that close to dry that a momentary interruption of fuel to the pump could cause them to starve?(as the fuel connector jiggles?) Thanks again,<br /> Pat in MD

 

[johnkc]

Re: Merc 100 fuel delivery

pat, i have some tech literature on the pumps i can email or fax to you .need #or address.

 

[hackeyfly]

Re: Merc 100 fuel delivery

Thanks again, guys- I think I got a step closer to pinning down the problem this eve. Pulled the fuel pump and opened it up......I don't think the diaphragms are supposed to have the rubber peeling and flaking off of the cloth backing....This may be reducing the efficiency of the unit! I can sure use the lit. now, my fax # is 410-803-0119, email is hackeyfly@aol.com. Hopefully my aggresive priming of the bulb is what caused the leak at the quick connect. Will keep ya posted,<br /> Pat

 

[hackeyfly]

Re: Merc 100 fuel delivery

Rebuilt the fuel pump today, seems to have done the job. The old parts were really screwed up, hard as a rock and falling apart. Thanks again for all the help!<br /> Pat in MD

 

[hackeyfly]

Re: Merc 100 fuel delivery

Thanks for the fax- it was the same info that came with the rebuild kit-will go into the "Merc" file!