CONTINUOUSWAVE

My 1987 Mercury 1502-liter with oil system removed and using premix fuel runs strong and idles well. I love this engine, but:

—if run at idle or low throttle long enough, the engine stops drawing fuel, empties the line, and dies. If I pump the bulb back up, it fires right up and runs great.

—if run about 2500-RPM and on plane, the fuel line stays full and the engine runs great.

— the fuel lines that run carburetor to carburetor and carburetor to fuel pump are fresh, tight, and leak free, and the primer bulb pumps up firm and does not force any leaks.

This has been an irritating problem for the last two years in an otherwise perfect motor

A new diaphragm and gasket kit a year ago mode no improvement.

--Peter

The fuel pump is usually operated by vacuum pulses from the crankcase via a check valve. Examine that hose and the check valve.

Discovered something: The fuel pump on my motor was missing some internal parts: a spring with a disc on the end, to keep the diaphragm under tension.

I discovered those things were missing, by looking at the manual... Which I had not done up to this point, because I hadn't really needed to. I had been using this motor with the slowly dying idle for the last four years and it was just never a big enough deal to move up my priority list. History: I got the powerhead used, rebuilt the carbs, Chris Carson reeds, new bleed lines, new fuel pump kit (which did not come with spring and disc), dropped it on and it worked just fine except for slowly dying at low rpm. I was new enough to Mercury that I had no idea that parts were missing... until I actually looked at the manual the other day. When I looked at pictures of the kits online, I had no idea that there was even supposed to be a spring and disc... until a couple of days ago... Because none of the pump kits I looked at had a spring and disc.

And I have still not yet seen a pump kit with a photo that had the spring and disc. For some reason the kits for lower horsepower motors look exactly the same, and DO show the spring and disc in the kit. But not for the 150-225 hp Mercury V6.

Oh well, I ordered them separately now that I know about them.

I took the boat out yesterday and it basically seems like problem solved, though I'm not the type to jump to conclusions after one test. I'll report back later if the problem persists even with the missing parts in place.

-Peter