1988 mercury 35 - stalls idling in forward

[Baitcooler]

I can idle it in neutral in a barrel and it’s ok. I can run it on plane and it is ok. When idling in gear in a no-wake or trailering situation it stalls and I have to prime the bulb again to restart it

I have a parts motor. I was considering swapping the fuel pumps as a troubleshooting step. Does that make sense?

The primer bulb, fuel line, quick-connect fittings are new. The tank is a newer west marine 6-gallon tank.

Let me know now if you can add any insight. Thanks!

 

[Baitcooler]

Just for clarity I'd like to add that it doesn't stall immediately when shifted into gear, but will idle fine for 30 seconds to 1.5 minutes maybe.

Weeks ago I measured idle speeds in a barrel in my side yard. Engine speeds seemed in the ballpark. They were 1150-ish in neutral and 850-ish in gear. I was using a tiny tach on the #1 plug and a DMM on the rectifier comparing RPM to pulses-per-second so I could find a tach gauge for the helm. I never left it in gear long enough to experience this stall-out problem.

The motor is new to me. Thanks again, guys.

 

[SteveVT]

Have you adjusted the idle mixture?

 

[Baitcooler]

No but I’ll check it next time I work on it. Is it 1.5 turns out? Find too rich, find too lean, split the difference and cheat it slightly rich?

I have the old scanned service manual for all 2hp to 40hp 2-strokes. A ctrl+f search is worthless.

I felt like if it was the idle mixture setting it would stall immediately when I shifted it into gear. I get some time in gear before it stalls. Long enough to start fiddling with a fish finder... when it does hesitate increasing throttle doesn’t help, it just brings on the stall quicker. On the water I was by myself but I felt like if I had someone with me who could have just squeezed the primer bulb and it would have worked ok. I’ll test that scenario in my trash can setup when I work on it next.

 

[Baitcooler]

After work I filled up the trashcan and cranked it up again. I let it warm up some in neutral then put it in gear. I waited. When it started to hesitate I reached for the primer bulb. It was soft. I pumped it until it was firm. The motor recovered and did not stall out.

I took off the cowling and removed the fuel pump. When disassembled, I noticed one of the check valves was slightly damaged. I rebuilt with the kit I ordered and reassembled. I started the motor and let it idle in gear waiting to see if the trouble went away. It seemed OK. At one point I got paranoid and thought it was sounding worse so I reached for the bulb but it was firm. I'll know for sure on the water, but I think I found and fixed the trouble.

The hardest part was lining up all the gaskets and diaphragms on the motor when reassembling.

I checked the idle mixture setting. It was 1.5 turns out. I moved it around some and didn't really notice a difference, so I just put it back. I'll revisit that later.

Thanks All!