Troubleshooting Twin 1995 150HP Mercury Black Max Motors?

Question

I have already rebuilt the fuel pumps and have had considerable performance improvement. Both motors are exhibiting the same problems to varying degrees at different times. The problems I have now are intermittent hard starting, cold or hot, consistent excessive smoke at start-up and at idle, and stalling when shifting into gear. High speed performance is good. 45+mph (gps) at 5000rpm. It is not the matter of not being able to perform the necessary work but rather after rebuilding the fuel pumps I have no idea what the next step(s) should be. I expect there will be several hopefully minor fixes/adjustments to be made but I have no idea where I should start and what path I should be on.

Compression is in the mid range for the year model with less +/- 2.5% difference across the cylinders

Thanks in advance

Answer 1

Sound like you have crank seal problems.

Clean the carbs, do the tune up things.

If this doesn't work, look at changing the seals on the top of the engine first as they are the easiest.

Answer 2

i am thinking that your engines are carburetor. and it sounds like you may have clogged jets in them. the easiest way to find out if that is your problem is to hit the choke when you feel the engines getting ready to die out on you. if they pick back up, you need your carbs cleaned... my next guess would be guck in the fuel tanks... as the tanks are probably at least as old as the engines.... 17 years... if not carbs then check out your fuel tank... and i would ( for future purposes ) install an inline fuel filter to keep the "junk" out of your engine...

Answer 3

Well, you've already rebuilt the fuel pumps..I'm assuming you rebuilt the carbs, the whole nine yards? There are a ton of things you can do, but it sounds to me like your carbs need to be adjusted for fuel/oil mixture and idle. Those engines should idle at anywhere from 700-850 without a problem, but about 800 makes them perform really well at idle. Some folks may tell you that two cycle motors aren't made to idle, but if tuned properly, they should idle for quite a bit without any trouble. Make sure your carbs are cleaned out, check your mix and then check your fuel lines. If you do it yourself, it's cheap insurance to replace your fuel lines, bulbs and all. Someone above me said to run it on portable tanks, and that's a great idea. We do that at our marina once in a while to be sure of problems on outboards. The first thing you'll want to do is turn your idle up a little bit while you're working on the fuel/oil mixture, that way if you richen it up too much while you're messing with it it won't stall out on you as easily. Then just go from there, but make sure you don't lean it out too much!! You know what'll happen...

I also wanted to point out to you that those 150's are made to run up to 5500 RPM's and I highly recommend you pitch your props down to get into that range. You'll get a little more top end and a wider RPM range of performance. You'll also notice a bit more holeshot performance as well. Good Luck with your  boat!

Answer 4

Before you go any farther on the engines....I have to ask.....Have you ensured that your problem is not your boats fuel tank or fuel lines?  You may be pouring money into the engines, when your problem may be your boats fuel system. Try running both engines on portable tanks to see if they act differently.

Answer 5

yes i do agree with the last comment of fuel tank and primer ball..quicksilver had a problem with the seals on primer balls and needed to be replaced with the yellow seals.