Desperately need help from the 40 Merc guys

[BRzuki]

Where can I get the other size jets at specifically the 56's?

[Fastjeff57]

I wouldn't leave that filter after the pump out or you'll really have carb problems!

Are you reading plug colors? That would tell you a lot.

Jeff

[BRzuki]

I'm running a water/fuel filter separator so I have no worries of getting trash in the carbs.

I ran the motor yesterday and tried pumping the bulb with no change in performance, the fuel filter removal didn't help so I ran it at WOT for a little bit, pulled the kill switch and checked my plugs. Top plug was almost completely black, middle, and bottom plug were tan, but darker than what I would prefer. Obviously the top cylinder is getting flooded. After making a call it was brought up that it might be my fuel pump since it is partly actuated by the top cylinder. I luckily found a fuel pump kit at a shop a mile away and rebuilt the pump. One diaphragm looked good while the other had rubber delaminating. I ran out of time to run it again except at the house on a hose. I'm hoping that was the problem and it is fixed now.

I also put .060 main jets in one set of carbs and .058 mains in another set. Will test tomorrow to see if my top end problem is fixed and if I need to lean out further.

Thanks for all of the help guys.

[Bill Van Steenwyk]

Since you have asked for help, I will make a few more comments.

Usually complete fuel filter removal would not be recommended, especially a filter that was your last line of protection between the fuel pump and carbs.

It is very easy to check blockages by blowing into the fuel line on the tank side of whatever filter you want to check if you have multiple ones in the system, by disconnecting the line to that filter and then blowing directly into the filter itself. If difficult to get your mouth on the end of the filter, put a piece of tubing on it for better access. The reason for doing it that way would be to eliminate the possibility of letting anything that has managed to get past any other filters you might have, and is just sitting in the lines, have a direct path to the carbs when the last line of defense is removed (the filter you just took out).

You mention a water separator/filter that will take care of preventing anything from getting to the carbs, after the filter removal you report. Unless that filter/separator is located between the carbs and the fuel pump, by removing the filter you describe, you now have a direct path for any crud or corruption to get into the inlet needle seat portion of the carbs.
The reason I mention this is most water separating filters I have seen mount on the transom of the boat just upstream of the tank. Even if you are using a small "spin on" type, mounted on the motor itself, by removing the filter between the pump and carbs you still have the path I mentioned previously. Remember that there are other types of trash that can find their way into a fuel system, not just what might be in the fuel tank or fuel that you put in the tank. Inner lining of the fuel line, parts of the pump diaphram, and other things can get to the carbs from several sources. It all does not have to come from the tank, or even from between the pump and carbs. It can just be sitting in the fuel line, waiting to be pushed into the carbs if not protected by a filter.

All that being said, the other tips you have gotten from other posters may very well have you on the right track, if you have two plugs completely black, ALTHOUGH they can be this way if you do not perform your plug check from WOT as pointed out and described in an earlier post. I have a 150EFI Merc V6, and my surface gap plugs are ALWAYS black, unless I perform a plug check the way described. They will be black and sooty every time if I just put the boat on the trailer normally, and then pull the plugs.

One thing you did not mention in your original post was the sound of the motor when you went from the part throttle operation to full throttle. In addition to slowing down (or just not going any faster) did the engine sound like it was "four cycling"? If you know what I mean by that term, there is not much mistaking where the problem lies. It would almost certainly be too rich as several posters describe. Four cycling can be most clearly described as when the motor is at WOT there is no doubt all cylinders are NOT firing EACH REVOLUTION of the crank. When "four cycling" it sounds as though the cylinders are only firing ever other time, hence the term "four cycling", as normally you would consider normal operation as "two cycling" and firing normally, 3 times every revolution, as that is the type motor it is. (3 cylinders, and two cycle)

Hope you solve the problem and be sure to let us know. Also if you are using ethanol laced fuel, be sure and use all the fuel filter protection available, as the ethanol in the fuel will "scrub" the fuel tank, acts as a solvent on some fuel line, (although most fuel line sold now is supposedly ethanol resistant) and then all that stuff gets carried into the engine.

Good luck

[BRzuki]

I did the WOT/kill switch plug check on the water and not on the trailer. The plugs were as described. Only the top plug was black. The middle and bottom plugs were tanned.

I'm not sure if it was four-cycling or not, but the motor makes a different noise, like its getting bogged down.

I'll put the inline fuel filter back on as this made no difference in performance from my testing.

Thanks again.

[fs5]

your top carb might have a crap in the needle and seat mate.my top cylinder is always leaner then the bottom 2.
i had some dramas a while back where ethinol blended fuel deteriorated my primer bulb ,as in it dissolved in the fuel and made it through the the screw on filter fitted to the motor and clogged up the needle and seat flooding the carbs.but it did it on all 3 though.
its easy enough to see,it looks like a dark cloud/sludge in the filter bowl as you prime it.i run a inline fuel filter aswell nowdays and i havn't had a drama since.maybe worth looking at.

any merc dealer can get you the .056 jets,there exspensive little buggers they cost me $15 each over here.

[Bill Van Steenwyk]

if your fuel system looks to be OK after the other checks and jet change.

You mention on another site that the top plug is black but the other two look to be OK.
You might check for steady fire on that cylinder, WHILE UNDER LOAD and WOT, with a timing light around the top plug wire. If you go to that trouble, check them all.
Faulty ignition to that one plug could cause a problem, especially if you have a separate coil for each plug. I had a coil wire slip almost out of a coil on my V-6 but could not tell it until I pulled on it because of the "boot" over the access for the wire into the coil. The wire had come almost all the way out and was at least an inch or more from the contact up in the coil but was not able to see it because of the boot.

[proprider01us]

I had the same thing happen to me at a race this past season on my 4cyl Merc. Didn't find the problem until someone grabbed the wire and pulled on it. Since then, I've run a nylon tie wrap around each end if the plug wire where it attaches to the coil boot and plug boot.

if your fuel system looks to be OK after the other checks and jet change.

You mention on another site that the top plug is black but the other two look to be OK.
You might check for steady fire on that cylinder, WHILE UNDER LOAD and WOT, with a timing light around the top plug wire. If you go to that trouble, check them all.
Faulty ignition to that one plug could cause a problem, especially if you have a separate coil for each plug. I had a coil wire slip almost out of a coil on my V-6 but could not tell it until I pulled on it because of the "boot" over the access for the wire into the coil. The wire had come almost all the way out and was at least an inch or more from the contact up in the coil but was not able to see it because of the boot.

[BRzuki]

Got a chance to run the motor this evening after putting a new fuel pump kit in. It ran like a scalded dog. 400 rpms and 3 mph gained. I ran the .060 jets and did a WOT electrical shut down plug check and I need to lean it out a little more, but .058 is as far as I'm going to go down. Don't want to lean it out too much for when I'm running it in temperatures 30 to 40 degrees cooler than I ran it today.

[Bill Van Steenwyk]

Congratulations on the improvement in the way the motor is running now versus when you first posted.

One question: In your latest post you mention you put the fuel pump kit in and also changed jets, going down to a 60 I think you said. Did you make BOTH these changes at the same time?? If so it is difficult to figure out just which one of the changes made the most difference and/or actually solved the problem.

Reason I am curious is picking up RPM and speed after a fuel pump kit would almost certainly mean too lean as I first suggested, while improvement with the smaller jets would tend to point towards too rich as the problem as one or two others that were trying to help suggested.

I am sure you are very happy that the motor seems to be fixed now or at least running much better, but it would also be nice to know which thing you did solved the problem.

One thing you always want to do, at least when testing to try to improve performance (maybe when not just trying to fix a problem) is only make one change at a time. That way you know whether you are hurting or helping whatever you are trying to fix.

Glad it is running better now and hopefully you learned something from the problem with the motor this time that will help you in the future. You will not only save some money, but there is much satisfaction in solving problems like this yourself.

ADD: Another possible solution to what may have improved the running of the motor is that there was some obstruction in the line PARTIALLY blocking fuel flow and it ran out unnoticed with fuel when you were removing/reinstalling fuel line during the process of trying to diagnose and fix the problem. Also possible that the problem was caused by a little of both things you changed. Sounds like based on others experience with this same motor you were maybe a little rich for optimum running from the start which is the way motors usually are from the factory, and then you had the fuel pump problem come along and compound the problem. Another reason to be sure and let us know if you made both the changes at once.