1985 merc 3.7 runs well only 15 min.

[Joral]

I have 1985 mercr 3.7 Alpha. It was winterized last year after running well during the season. This year I have taken the boat a few times and it runs well for about 15 - 20 minutes and then starts missing, lossing power, then slows down for a little bit and then shuts down. It may start a few times after that but it gets harder and harder if I don't let it sit for a while I cannot go back to the ramp. Unrelated to this problem at the begining of the season, the same boat dealer changed the water pump because they told me it may need it. Recently I had the carburator cleanned and the gas filter replaced and added dry gas by a car mechanic and it still has the problem. The same car mechanic tested all electrical at his shop and says everything is fine. He coudn't replicated the problem at the garage. (Maybe he did not run it long enough). He also added something to the gas tank to clean it. I appreciate any help that anyone could give me. At the boat dealer they told me that it would take a long time to diagnosticate for them because they will have to do it piece by piece and it also would be very expensive.
Thank you

 

[Don S]

Re: 1985 merc 3.7 runs well only 15 min.

Read this,
http://forums.iboats.com/showthread.php?t=283269

 

[Merc4ever]

Re: 1985 merc 3.7 runs well only 15 min.

I had a similar problem...starts and runs fine then runs funny and keeps getting worse as I go. I talked to a couple other people that had the same thing.

I found the check valve inside the brass connection for the fuel line was sticking. Mine was at the top of my tank inside the hose nipple. This is a common problem and others told me to take off the brass hose fitting out and pound a small shaft into the ball and take it out. It worked fine ever since.

One problem is that this gadget is a anti-siphon valve if you get a gas leak all the gas will siphon out of your tank and into your bildge. Coast gaurd wants you to keep them in there. I just keep an eye on my fuel lines and check often for leaks.

 

[Joral]

Re: 1985 merc 3.7 runs well only 15 min.

I took it back to the mechanic. It is showing engine oil in the carburator. This happens when the motor goes at high RPMs. The mechanic now has separated the hose that goes from the engine to the carburator and connected a new hose with a drainer to the motor. The carburator has the arrestor without connecting to anything. I would appreciate any comment and advise.

Thank you.

 

[Joral]

Re: 1985 merc 3.7 runs well only 15 min.

Drainer did not work. Boat runned very well for about 20 min. Started to smell oil very strong and there after begin malfuntioning. After a moment or two motor would not even start.
Aparently oil is coming out from the engine at the air intake. This happens only it worms up really well.

Thank you.

 

[JustJason]

Re: 1985 merc 3.7 runs well only 15 min.

start with a compression test....

 

[guyaverage]

Re: 1985 merc 3.7 runs well only 15 min.

Your intake manifold may be bad. It seperates the lifter/pushrod area (oil), two water passages on the ends, the #3 crossover exhaust port, and the intake tracts all from each other. Remove the intake manifold and check it out. Its a $4 part.

 

[Joral]

Re: 1985 merc 3.7 runs well only 15 min.

The boat is at the boat mechanic. Initially couldn?t find the problem because the boat sounds and runs very good at the beginning. He did oil pressure check. Said that pressure was 20% off in all cylinders but that was not too bad because up to 15% is normal. After he runned the boat for a while, was able to see that when it warms up well or 15 minutes of running starts missing and shouting off. He said then, that the battery is not charging well. He connected a direct wire form the positive of the battery to the positive of the coil and that apparently is fixing the problem. He needs to change a regulator in the alternator to make sure that the battery charges well (expensive part. He thinks that after he changes this, that all the other problems will be fixed. I appreciate opinions on this. Thank you.

 

[JustJason]

Re: 1985 merc 3.7 runs well only 15 min.

you may want to find another mechanic..... especially if he's changing a $$$700 voltage regulator on a "gut feeling".