Johnson 175 Powerpack Problem?

[dwco5051]

I recently picked up a 1990 Johnson 175 VRO for next to nothing and am having some problems now with it. It will run like a top for 10 or 15 minutes than suddenly dies at high speed. When it dies it will run OK at low speed, sometimes around 1800 RPM, sometimes up to 2200 RPM. It will continue to operate well until I advance the throttle then it quits. If I back off the throttle right away it will keep running at the lower rpm's. Replaced plugs and after running they were wet which makes me think it is a ignition problem. I am currently running a non-VRO fuel pump and 50/1 with a section of clear plastic fuel hose. No bubbles and good fuel pressure. Engine temp does not set off the sensors and I have checked external head temp with an infrared thermometer and they range from about 140 to 160F depending which cylinder I read. Compression is about 85 on all six cylinders with almost no variation.

I am in the process of building a new house so I haven?t had a lot of time to work on it as the lake is 35 miles away. I am thinking of hooking up a couple of timing lights (one on each bank) and observing them while I run to see if the ignition dies when the problem occurs but I have not been able to get to the lake for two weeks.

Question ? Am I on the right track? Could this be a powerpack problem?

 

[emdsapmgr]

Re: Johnson 175 Powerpack Problem?

Using an inductive timing light on each plug wire will show if they are firing when under load. Good idea. Expect to see strong, constant, rhythmic flashes on all 6 plugs. You are looking for intermittent or weak flashes. Electronic issues do tend to show up after the engine reaches normal operating temps. You may also have a weak fuel pump. When the engine starts to stumble, squeeze the fuel hose bulb repeatedly and see if it will pick up and run full speed. If it stays running with you priming the bulb, the pump is suspect.

 

[tashasdaddy]

Re: Johnson 175 Powerpack Problem?

have you check the carbs? i would check the spark as you said.

 

[dwco5051]

Re: Johnson 175 Powerpack Problem?

This motor had a weak fuel pump on the first trip. Went almost two mile steering with my feet and pumping the primer bulb stretched out on the back casting platform. Replaced it with a straight pump and filled the aux tank with 50/1. This is the point where it ran good for ten or so minutes.

I did forget to mention when the engine cuts out I can put it in neutral and it will go right up to top rpm when I advance the throttle. I thought maybe a weak spark would not fire under load.

 

[sanfordmj]

Re: Johnson 175 Powerpack Problem?

It may be a bad temperature sensor making it run in slow mode.