Merc 140 3.0 engine problems

[kbetts]

Hi all, I am having a few issues with my 1979 181 Merc 3.0 4 cylinder with the alpha outdrive. The boat had been stored for roughly eight years before I pulled it out and started to work on it, that was two years ago. I had to pull the engine, because I had a broken off starter bolt in the block. While I had the engine on the stand, I had the machine shop rework the head (valve job and hardened seats for unleaded fuel) and I replaced the oil pump. I also rebuilt the Rochester carb and installed a Petronox(sp) electronic in place of the points system in the distributer. I also replaced the rotor bug, Cap, plug wires, plugs, installed a water separator, and new fuel filter on top of fuel pump. I also have fresh fuel in now.

Here are the issues I am having. I have a knock or ticking sound coming from the valve cover, I believe. I have adjusted the valves at least 4 times, as it calls out in the Merc manual. The tick speed does increase while the motor rpm's increase, but doesn't seem to really get any louder. I have ran the boat on the water like this, without any problems...luckily. Could I have a collapsed lifter making that noise? I don't recall the valve train making this noise before disassembly.

The next issue I am having is with the timing and the carburetor. The carb is the Rochester carb with the two adjusting screws adjusted out 1 1/2 turns from seat as manual calls. I have the timing set at 6 degrees BTDC with a timing light and #1 spark plug at idle. Off of idle the motor wants to stumble before revving up. The motor seems to like life better the more I go BTDC. I believe I have the valves adjusted correctly, the timing set correctly, and the carb roughly dialed in. Could the advance springs in the distributor be wore out causing me a timing issue?

I probably only have 10 hours or so on the motor after all of this work. I hope I have given the pro's enough info about the problems I am having to help me in the right direction. Thanks in advance.

 

[cheburashka]

Re: Merc 140 3.0 engine problems

You'll have to isolate the ticking sound. Figure out which of the cylinders it's coming from. When you tore it down, did you keep everything in order for reassembly? Could be that you mixed up the pushrods or the lifters. I don't know about collapsed lifters.

As to the timing, yes it could be a bad advance unit. Did you inspect and lubricate the unit when you installed the Pertronix kit? Did you verify the advance with a timing light? You should be able to see the flash advancing across the timing plate when you rev the engine.

These engines will bog coming off of idle for a lot of reasons. Timing is one. Bad accelerator pumps is another. Are you sure you got the check balls back in the right place in the carb? They're notorious for causing acceleration problems.

 

[Don S]

Re: Merc 140 3.0 engine problems

The carb is the Rochester carb with the two adjusting screws adjusted out 1 1/2 turns from seat as manual calls

.
As I just posted in another thread, that adjustment is only a starting point, it is NOT the final adjustment. Get the timing to what the book calls for the with the engine warmed up, adjust the idle mixture and speed. This has to be done on every engine, because they are all different.
You can also check the advance, just use your timing light and see if the timing mark moves as it should. This can be done on muffs, doesn't need to be under load.
Get the mixture, idlespeed, timing and advance timing right and the engine will probably stop stumbling.

Your ticking may just be a bad lifter.

 

[kbetts]

Re: Merc 140 3.0 engine problems

cheburashka, I don't recall if I kept the rocker arms and push rods in order. This has been two years ago, can't remember that far back. As for the lifters, I don't recall even removing them. It sounds like the ticking sound is coming from the #3 or 4, it's toward the back of the motor.

The original distributor started to cut it's self in half from the inside like a fly cutter. There were a bunch of fillings on the inside of the distributor. I bought a used one off Ebay, and installed the kit in that one before reassembly. The newer one looked to be from a newer motor, I believe from a mid 90's model, but looked just like my old one that I took out. I did check the distributor before assembly, and everything looked to be fine. I didn't check the advance with a timing light, but it's on my list of things to do for tonight.

I am pretty anal about assembly, so I believe I got the check balls back in the proper place in the carb. The cost of a gasket kit is small, so I might take it back off and double check to make sure. I didn't even think about that to be a cause. The engine starts and runs at rpm fine, just stumbles off idle.

 

[capthook]

Re: Merc 140 3.0 engine problems

6* BTDC? I think the book states 8* BTDC? Don correct me if I am wrong. One thing you can also do is bring your number 1 piston to top dead center and check your mark and see if its alingned with your timming tab TDC mark, and also pull the distributer "CAP" and see where the rotor is pointed it should be pointing to number one as well. If it is not let us know.

 

[kbetts]

Re: Merc 140 3.0 engine problems

Good to hear from you Don.
I understand that this is just a starting point for the carb adjustment. I do have the motor timed and carb roughly set to the book and the idle speed set from a tach from a dwell meter. All of these adjustments were made on the muffs. Could the stumble be caused from a bad lifter not letting the valve open and close properly?

capthook, you are correct on the timing. It is set @8 BTDC not 6 BTDS as I stated. I did check the timing mark with the rotor when I adjusted the valves and all looked good.

 

[Don S]

Re: Merc 140 3.0 engine problems

Actually, the timing is supposed to be 6? BTDC on the 140, the 120 engine is 8?. Did you set the dwell (not just gap) before setting the timing?
I doubt that a lifter ticking will cause any running problems. Might just try running with the valve cover off, find out which one is ticking and see if a little tighter or a little looser will cure the ticking problem.
Also look and see if you have the same amount of movement for all rockers.
Then, after all that, readjust the idle mixture. After engine is warm, and at proper idle speed, with throttle cable disconnected, adjust mixture screw in till rpm drops slightly, then back out to best rpm. Do this several times to each mixture screw after you have that adjustment back each screw out an additional 1/8 turn. (No, more isn't better) then see if you have the stumble.
Also while doing the mixture adjustment, rev it up occasionally to keep it cleaned out while adjusting.

 

[kbetts]

Re: Merc 140 3.0 engine problems

Don, I will correct the timing to 6 BTDS. The closer to TDC I get, the more the motor wants to sputter of idle. I have the electronic Pertronix system in place of the old points system now. Do I need to set dwell on the Pertronix system? I am not sure how to do that. I am sure I have thrown away the instructions on that system, but I will try to look up the site and see if I can locate them. Honestly, I can't remember the proper way to set the dwell with the points system, it has been awhile since I messed with that. I do remember using a dwell meter with the tach on it to set the idle speed. I will try to readjust the valves with the valve cover off to get rid of the tic noise and readjust the carb the way you described.
If I can't get rid of the ticking noise, will it be OK to replace with new lifters on a used cam? Lots off assembly lube?
Another question, when you adjust the mixture screw out, are you going richer or leaner?

 

[capthook]

Re: Merc 140 3.0 engine problems

No you don't set dwell. Just make sure that it is advancing correctly. I am glad I responded to your post about the 8*. I will be redoing mine tonight now. I have the stupid clymers manual so I guess going by what it says is like getting diretions from a 3 year old. Good Luck JB