1986 mercruiser 140 3.0L

[Jordan80]

Looking for help with my 1986 mercruiser 140 3.0L. It runs fine for about 15 minutes and then bogs at full throttle. I have cleaned the carb twice, changed the fuel pump filter, new plugs, new distributer cap, tried another coil, cleaned the anit syphon valve and new gas. Every time I go out, it's the same, fine for 15 - 20 minutes and then bogs at full throttle. It will idle and drive fine at low speeds all day long.

 

[Bt Doctur]

Run on a remote outboard tank , test and report back

 

[Jordan80]

Sorry, I'm new here and was trying to figure out how to post on the forum. I thought this was the forum.

 

[Lars k]

This is the forum. Its just general knowlege that we lose a lot of good information when people pm. Think its his standard text every time he replies

 

[Bondo]

Sorry, I'm new here and was trying to figure out how to post on the forum. I thought this was the forum.

Ayuh,..... Welcome Aboard,.... Odds are yer boat is runnin' outa gas, 'n the best way to diagnose Why, is to hook up a remote tank, eliminatin' the boat side of the fuel system,.....

If ya still have the runability problem, the fuel pump, or carb need attention,....

If the problem goes away,..... The gas can't get outa the tank,....

 

[Lars k]

It could also be Vapor lock. Its when gas from pump To carb tuns Into vapor due to high temerature. It would make sence from what u are descriping. Higher rpm = hotter engine. But then again it could 1 of several other things.

 

[Jordan80]

Thanks for everyone's feedback. I may be a new member but I can say that I have read threads on this website here for a long time before becoming a member. So last night I tore the carb apart one last time to clean it. Silly me did not realize that there was a fuel filter right where the steel line comes into the carb (rookie mistake). I opened that up and it was gummed up bad. So I cleaned it out. I'm taking the boat out tonight to test it. I also brought an external tank and will try that just in case it acts up again but I'm guessing that the filter was the problem. I only ever changed the filter in the fuel pump before and didn't stop to think there was another.

 

[Jordan80]

OK so.... Didn't work. Ran at about 90 percent full throttle right off the start and you could feel it sporadically stutter. I tried a separate tank and no change. So while I was on the lake, I took the fuel pump filter out (the one I just replace) and it ran better. I could get 100 percent throttle but it would still sporadically stutter. Make me think the fuel pump is having a hard time pumping the gas up (easier passage without the filter restricting it).

 

[Rick Stephens]

If you had a crud filled inlet filter you have crud in your carburetor. Rebuild it. Get a vacuum/pressure tester and also test your fuel line pressure.

 

[Jordan80]

I've taken the carb apart and cleaned it 4 times. I keep hoping to find something new but I don't. This last time is when I pulled out the inlet filter. So I can tell you the carb is absolutely clean and particle free. I think I will have to test the pressure to determine if my fuel pump is working right.

 

[Rick Stephens]

Sounds like the next thing. You can test both sides of the pump. Funny I never thought about it before, but achris is right that testing the suction side will tell you more than testing the pressure side.

 

[Jordan80]

So I just took the fuel pump off and took it completely apart. Diaphragm looked good with no cracks or anything. Under the diaphragm (where the spring is) actually had clumps of a black gummy like substance (maybe oil/grease) dried up and clumped. Actually plugging the the rubber line that runs back up to the carb. So I cleaned that out and blew it all out with compressed air. I'm going to try that before I invest in a pressure tester. Won't be able to test it for a couple days now (wait for my next day off work). We'll see If that plugged line was the culprit.

 

[Jordan80]

Hi everyone, I've been away from this forum for a little while but I wanted to share what I finally figured out that was wrong with my boat. After 20 minutes of driving my 1986 mercuiser 140 hp would start to bog down. It would idle all day long but bog down at full. I rebuilt the carb a couple times, replaced the ignition coil, cleaned vent valves, fuel lines, cleaned the fuel pump etc... but nothing worked. Turns out it was the condensor (in the distributor). My ignition was made of an ignition coil (with an external resistor) and points and condensor. Anyways, the external resistor had failed and the ignition coil was getting the full 12 volts (only supposed to get roughly 9V. In turn it was sending too much power to the condensor causing it to heat up and fail after 20 minutes. I repleaced the coil with a 40,000 volt flame thrower coil (it has built in 3 ohms resistance) and got rid of the points and condensor and went to an electronic ignition. The coil and electronic ignition only cost me 100 bucks total. And voila, runs like a charm again and lot better on gas now. Just thought i would share this in case anyone else was having similar issues

 

[nola mike]

Interesting. I would think that you'd fry the points and it would never run right. Thanks for the update