1984 Mercury 115 6cyl

[phebus1]

Out on lake yesterday, motor running great. Running at a steady 4400 rpm and motor starts missing and breaking up badly. Throttle down and idles and runs fine. Accelerate again, and motor runs great to 2500 rpm then starts missing badly and loses power.
Carbs were rebuilt and synced, new fuel lines, filter, fuel pump rebuilt, etc. and pumping bulb does not change anything so, I'm thinking the problem is electrical. Going to do a compression check before I do anything else, but my gut is telling me that my problem is either the rectifier or stator,
If compression good, getting meter out and going through ignition system.

Any help or constructive comments appreciated.

Thanks

 

[phebus1]

Re: 1984 Mercury 115 6cyl

A little follow up. Compression was good on all cylinders, so I proceeded to check stator. Red, red/white wires were both within spec at 150 ohms. Blue wire was within spec at 6200 ohms, but blue/white wire was out at 12500 ohms.
New stator ordered, and hopefully that will cure my problem.

 

[Texasmark]

Re: 1984 Mercury 115 6cyl

Sounds great. Was your WOT 4400 rpms normal (indicating a problem) or was it lower than what the engine usually runs?

Mark

 

[phebus1]

Re: 1984 Mercury 115 6cyl

4400 was a cruising spped. The way it is propped, 5500 is wot. Started missing really bad While cruising along at the 4400, so shut it off immediately and checked fuel and lines to make sure there was no obvious problems. Finding none, started it up again (we were out in middle of lake) and it started and idled great. Throttled up and it would run perfect until engine reached approx 2500 rpm. At 2500 rpm engine started missing again badly. As long as engine was kept below 2500 rpm it rann great, so we took it in at 2200 rpm and called it a day.

 

[Texasmark]

Re: 1984 Mercury 115 6cyl

The 5500 WOT says your setup including prop are perfect. I had a tower that I could run out of gas at WOT I got a 3/8" fuel line and got some of the kinks out of it and solved the problem. If the squeeze bulb is collapsed or has no resistance that would be your clue to running out of fuel from the tank. So, if the bulb changes nothing, what is it like before you use it in attempting to solve the problem?

Mark

 

[phebus1]

Re: 1984 Mercury 115 6cyl

Thanks for your feedback, but I'm not sure what you are asking.

Boat was running perfect with a good hole shot and and would accelerate to 5500 rpm and remain constant. Then while I was cruising at 4400 rpm the boat started missing really bad. Checked fuel lines and bulb just to check that the issue didn't seem fuel related. Fuel delivery didn't seem to be the issue, so I assumed it was electrical. Engine started and ran fine up to 2500 rpm where the miss and poor running started. Took boat in while running 2500 rpm with no issues.
Once home I started checking the elec. system with my meter and dva adapter. Checked stator per the cdi troubleshooting guide, and found the red wires to be within spec, but one of the blue wires had double the resistance it should have (13k vs. 6k). Ordered new stator and hoping that my issues are solved.

Thanks

 

[Texasmark]

Re: 1984 Mercury 115 6cyl

Sounds good. One of the biggest problems is: Is it spark or fuel.

Mark

 

[phebus1]

Re: 1984 Mercury 115 6cyl

Mark, when you ran the 3/8" fuel ine, did you go all the way to carbs with it, or just from tank to fuel pump? If all the way to carbs, how did you change the fuel fittings on carbs? While the motor is down and I'm waiting for parts, I'm going to change out the fuel line to 3/8".

Thanks