My trusty 500 Thunderbolt let me down today, looking for suggestions

[hotrod53]

1977 Mercury 500, thunderbolt ignition, 4 cylinder, no distributor, new plugs, new fuel line from the tank to the fitting but not inside the power head, full tank of fuel, StarTron treatment in the mix. The last 4 years it ran flawless, this year its been in the water for 4 hours and today it all went bad.

I'm at full throttle heading upstream for about 2 miles. My pee stream is good, no issues there, no weird noises. All of a sudden I went to half power as if I lost a cylinder for about 10 seconds, then 1/4 power, then not much power at all. I checked and I still had a good pee stream. I then went to neutral and it idled but not well. I tried to power up and it tried, then went down on power, then very low. I turned off the motor and let it sit for few, then I cranked it to see if it was free, no issues there. I pumped the ball and tried to start it, it sounded like it was flooded. Later on down the river, I could get it to try and start with the enricher all the way up but no good. Problem was I was 7 miles from my dock and my trolling battery was going quick! I had to call my brother and get rescued.... thank goodness for cell phones!

I'm thinking new fuel lines inside the power head to start, check the plugs which are new, maybe rebuild the fuel pump. Any more suggestions? And yes, a compression test may be in order.

 

[GA_Boater]

Start her up on muffs and see if the idle improves as you squeeze the bulb. That's a sign of the fuel pump needing a diaphragm.

Check the compression too.

 

[Mercurylips]

This sounds oddly familiar. My 1977 50 did the same this spring. The main fuel nozzle had dropped below the throat on my top carb( unbeknownst to me and my professional help) and wasn't getting a good hole shot. Then it dropped out and left me in the lake. When we took it apart after getting it to my shop, we found the nozzle in the bottom of the float bowl. I decided to take them both off and after putting it all back correctly, the motor starts and runs like a new one. 50 miles of bad road up to the lake after the main highway was more than likely the straw that broke the camel's back, vibration on the washboard doing it in. I had previously rebuilt the pumps, carbs and installed new wiring including a new stator. The fuel lines were cracked and loose and some gaskets missing. All replaced and repaired over a two year period. Just didn't notice the nozzle missing from the throat but I did find the venturi wing in the splash well. DUH.

 

[hotrod53]

No Title

Thanks guys, here's what I've done so far. I first pulled all 4 plugs and looked them over, each looked good. They only have about 5 hours on them, I cleaned them and reinstalled them. I looked in the bore of each cylinder except for #4 since its down in the cowl, no apparent piston damage. The safety switch module looks horrible, the insulation was off and the wire was all corroded and green, its about to break, going to replace it. I replaced the fuel line from the inlet to the power head to the tee where it splits to the two carbs. I plan to replace those but have to buy it yet.

Are there any inline screens or filters in here other than in the carb inlet? I probably should rebuild the fuel pumps, if I remember the pump kit was different from the carb kit. One carb is a pain on this motor to remove, you have to remove the starter and I had to make a special wrench. I'm wondering if I should replace the fuel lines and condenser and try and fire it?

 

[Mercurylips]

You can and should replace that fuel line with automotive hose. It is very inexpensive. At the third try to clean adjust and repair my carbs, I still had a small piece of black junk from my old worn hose system. Found that in my main fuel jet. I also skinnied down a box end wrench for the upper carb. If it starts and runs fine (in the lake)you are home free. My experience tells me that there is more to do as evidenced by the crumbled and missing wire insulation. I also believe that is the tilt kill switch and not a condenser.

 

[hotrod53]

Update on the patient. I replaced the fuel line inside the power head from entrance of the power head to the the tee on the carb inlet. I also pulled the top bowl which surprisingly was bone dry. I also pulled the screen on the top carb and it was clean. After I did that I decided to leave the main disconnected and flush some fuel through from the tank to where the tee would go onto the carb...that's when the fun started!

When I pumped the ball I felt a slight resistance, then all of a sudden a tobacco colored glob of something blew out of the line and al over my chest. The goo then turned to a red color similar to the color of Stabil. This is odd because I use StarTron and my fuel is blue! I continued to flush until I got nice clean blue fuel.

I'll bet that I just found my issue. I need a replacement drain cap for my top carb tomorrow and I'm going to put the muffs on it and hit the key.

 

[Mercurylips]

I have to ask, what is a drain cap.......................another term for the float bowl?

 

[hotrod53]

My float bowl has a drain on the bottom of it with what looks like a cap from a Schrader valve on it

 

[hotrod53]

Very late update.... That redish brown snot-like substance was clogged in the connector hooking to the power head, it stopped all fuel flow! It looked to be coagulated Stabil that must have been in the tank. I flushed the lines and it runs like a top!