Rough running 'Rude

[GreenF350]

Well, what the heck...I can't seem to figure it out right now, so I will let you guys chew on it for awhile. I have a '91 40hp Evinrude on a Bass Tracker that I cannot seem to get to idle right to save my life. It runs rough at anything below say...about 3000rpms. This of course is causing me all kind of trouble getting it to idle right. It runs great 3000rpm+. So far I have replaced the coil (did nothing) the power pack/ignition module (Made it idle...it wouldn't idle at all before that) I also replaced the spark plugs (a few times over the last few outings), took apart and cleaned the carbs and also readjusted all the linkage and carb adjustments....What's left? I plan on replacing the plug wires this week, but they look and ohm out good. Any ideas? It's still on it's break in since I just replaced the powerhead (I bought it with almost no compression on one cylinder) and am still mixing it with extra oil, but this seems beyond the normal oil issues (plug fouling and not quite as much power). Hit me with some ideas and I will go from there. Thanks for any help.
-Aaron

[Robbie R.]

Fuel filter ?

Plug gap ?

Squeeze bulb tight ?

Robbie R.

[GreenF350]

Fuel filter is new....Plug gap is what my manual suggests...Can't remember exactly right now. .030 or .035 if I remember right. Bulb squeezes up tight and stays that way. I figure it may be something simple like that I forgot to check though, who knows at this point...lol. Thanks for the ideas though.
-Aaron

[zooker]

how about the gas tank vent?? is it open??

zooker

[1FASTLASER]

Just from what your saying it sounds like one of 2 things. Either you have a vacume leak or a set of reeds that arnt working smoothly. Hook the muffs up and have a couple cans of that cheap carb spray on hand. Drop the rpms down to the point where the motor starts to act up and with the spray tube that comes on the carb cleaner clean start to spray at all gaskets places such as the carb gasket,intake gasket....you get the picture. You will know when you find the leak becaus efor a brief moment the motor will pick up rpms and start to run fine. If you dont find a leak your gonna have to pull the front half off and look at the reeds. Do the carb cleaner trick first and lemme know what ya find. We will go from there. Hows that sound??

[mariner]

i forgot what this thing is called but my grampas 70 merc was doin the same thing, we replaced it and that done the trick

[1FASTLASER]

That would be the primer bulb. It really doesnt affect the idle unless it has a hole in it causing the fuel system to suck air. I am truly hoping his problem lies in a gasket leaking and not the reeds going bad and/or worn out. Its not a common problem but it does happen. And I assume he has just gone through this motor and what he is describing could detonate this motor again. A outboard that is running lean is a time bomb. Its not a matter if the motor will blow its when.

[GreenF350]

Well, I spent tonight rewiring for the new trolling motor, but tomorrow I will check for the leaking gaskets. I don't know why I didn't think of that....I used to be a certified auto mechanic before I joined the service. I did look at the reeds when I had the carb off and cleaned the snot out of them. I didn't see any chips, cracks, etc. that I am used to looking for on dirt bikes. What do outboards use for the exhaust side? Do they have a power valve like a 2 stroke dirt bike?

To answer laser's assumption, I bought the powerhead freshly rebuilt from a retired boat mechanic. He said it was good to go and I have actually called him with the problems I was having with it (There have been a few along the way) and he helped a bunch, but he now has cancer and has been pretty busy/laid up with that. I'm not sure how much anyone knows specifically about this motor, but just in case, here is the history of the problems...

-Kept blowing the main engine fuse killing power to EVERYTHING.
-------Bad ground on the choke solenoid.

-Developed a dead miss during break in that was not fouled plugs.
-------Sanded down and cleaned grounds for coil.

-Ran good at power but really had to be quick to get it in gear because it wouldn't idle at all and none of the timing or mixture adjustments did anything to change the way it idled.
-------Replaced coil (Epoxy was cracked anyway) didn't fix it, replaced ignition module, now it idles and adjustments make a difference, just isn't right yet.

Grounds seem to be a common problem, but I think I have checked all of them now and they are all good. I thought maybe the charge coils were weak, but if that was the case, why would it put out almost 16 volts at full throttle. (It's a 4 amp unregulated charging system.) I will check out the gaskets and get the plug wires replaced and report back. I appreciate all the help and ideas.

-Aaron

[GreenF350]

BTW, anyone have a test wheel for this motor I could rent? Timing has a baseline to be set at, but it is fine tuned by WOT timing advance and I have no way of doing it, short of standing over the motor with a timing light and hoping I don't fall overboard. As tempting as that is, it just seems a little too crazy for even me. I knew they would be expensive since if everyone had one, nobody would take it to the dealer to have work done on them, but $450 is too much for me to pay for something I MIGHT use once a year.
-Aaron

[mariner]

Originally Posted by 1FASTLASER

That would be the primer bulb. It really doesnt affect the idle unless it has a hole in it causing the fuel system to suck air. I am truly hoping his problem lies in a gasket leaking and not the reeds going bad and/or worn out. Its not a common problem but it does happen. And I assume he has just gone through this motor and what he is describing could detonate this motor again. A outboard that is running lean is a time bomb. Its not a matter if the motor will blow its when.

ya if it is messed up it want let the right amount of fuel in and so it want idol

[GreenF350]

Ok...Got some more info and quite a bit of insight into the problem....I have been having the suspicion that it was ignition not fuel and it looks like I was correct. Today I replaced the plug wires, checked for a leak at the carbs and just tinkered with it for quite some time. Here is what I found out....Hooked a tach to it that read off of the spark plugs....it's for 4 strokes, not 2 strokes....so that is why it is high, but here are the numbers, about 1800-1900 on the lower cylinder and (here is the kicker) about 2800-3000 on the top one. Since it is idling at about 1000 give or take depending on which tach I use (a mechanical on the flywheel or the boat tach) I assumed that the upper cylinder was double firing for some reason. I hooked up the timing light to the #1 plug and sure enough....it was firing every revolution just before TDC but running the timing light around the flywheel it is also firing, I guessing based on the position of the timing mark, just as the piston is starting to "come back up". That explains why I had to advance the timing so dang far to get it to idle....it brought it closer to the beginning of the piston going up having less affect on the way it is running. This is not good since it puts my boat down until I get this figured out, I don't see any signs of detonation on the plugs though, so hopefully nothing is damaged.

SO...any ideas on this one? I have already changed the ignition module...what else? The bottom cylinder is firing correct, so what is messing up the top? Now I am really confused.
-Aaron

[GreenF350]

Haha...Guess everyone is confused as I am. Well, I went to the dealer that I bought the ignition module from today. They said that the ignition module either had a 90 day or a 1 year warranty on it, then came the big whopper "Who installed the part?" That was me. I am no expert on boat motors, but I was a certified auto mechanic before I joined the military, I currently am a mechanic on airplanes, and I have been doing my own work on everything I own from lawnmowers to dirtbikes, to boats since I can remember. Well, they decided I needed to talk to one of their mechanics to decide if they were going to warranty it. He kept asking "Did you do ____" Everything he asked but one I had done. That was set the timing at WOT. (I didn't want to hang off the back of the boat at 35mph to check it.) He said that it he had never seen nor heard of an engine double firing like that and it must be something else. Nevermind the service manual I have specifically mentions double firing caused by that part. I'm kind of frustrated right now, but I will go back out tonight if the storms hold out and give it a look over one more time and then I guess I will be out-of-pocket for another $160 ignition module.
-Aaron

[flfireman]

That sucks. I was having similar problems w/ my 40 rude. After some poking around I had a small split in fuel line right before the filter. Unfortunately my fix was to go out and buy a new boat. Well, that's not a bad thing, the wife wasn't pleased when I told her it's only going to cost $15 for new fuel line.

[1FASTLASER]

Green
I been working on motors.........boats cars trucks for around 30 or so years. Coupld you possiblly scan or point me to a place on the net that talks about this double firing. Imyself have never heard of it. I AM NOT saying it doesnt happen. Lord knows I dont know everything. I can see how a sensor or something that if it got the wrong signal be it volts or ohms could fire more thanits supposed to but a coil to fire has to be told to do it. See what I am saying. What trigger are you talking about. Please be more specific and maybe between the 2 of us we can get you fixed up. I assume you OHMED out the ignition sysytem????

[GreenF350]

Yes, I ohmed the coil, before and after replacement, plug wires also before and after replacement, and checked everything I could without the "Stevens tester" that the manual refered too. Give me a few minutes and I will post up the info in my book. (I will scan it) For what it is worth, I talked to a machanic at another dealer and he said that he HAS seen it before and he has never seen it not fixed by replacing the power pack. Which is basically included in this module. I bought a new one today and will be installing it. I got it from the same place since they are the only ones that carry OMC parts and talked to a different guy. He seemed suprised they wouldn't warranty it and told me if this fixed the problem to come back and talk to him and he would see what he could do.
-Aaron

[GreenF350]

Well, It looks like my scanner may be on it's last leg, but here is a copy of the page. It is from a Clymer specifically for my ignition system (CD2U 4-Amp unregulated charging system).
-Aaron

[GreenF350]

Well, here is the update. It may hose me on getting the "old" module warranteed, but I think it will be fixed after Monday. I replaced the ignition module and then reset all of the linkage adjustments to the recommended starting settings. Cranked it over and it fired right up and idled better than it ever has....even being cold. While I was waiting for it to warm up so I could make some adjustments on it it died and wouldn't restart. So, while I am trying to figure out what the problem is I am looking back and cranking it over and I see this nice little stream of fuel shoot out of the motor everytime I push in the key. Upon further examination the manual lever on the enrichment solenoid is cracked and leaking. I figure if I go back in and ask for them to warranty a part and give me another one then they will figure that I am lying to them. I might try anyway, but I don't have my hopes up. It looks like when I am done it will almost be a completely brand new motor for 1/4 of the cost....lol. We'll see. Thanks again for the help and after I get the parts I will let you all know the latest update. I don't know why I never get the "normal" problems...lol.
-Aaron

[1FASTLASER]

Dont feel bad my friend. I always look for the simle things being wrong when to save time I should look for the mosy expensive part and or procedure be what I need to do. LOL Some of us just are lucky that way

[GreenF350]

Fixed it! The ignition module fixed the double firing and I think the bottom line on why I couldn't get it to run was my stupid oversight. The primary wire on the #2 cylinder wasn't all the way on. Got 'er back together today and it runs like a champ (at idle anyway, which is better than it was before). I'll take it out this weekend probably. Looks like the worst is over and it is just a few adjustments now.

On a side note, at the risk of showing my stupidity, I broke the key today while it was running...Wow, that makes some scary noises. I checked it all out though. No damage. I guess just snugging up the flywheel nut isn't enough. <---No sarcasm there.(It was pretty tight, but I was hoping not to have to get serious with the puller if I took it back apart) No harm, no foul. Rest assured I won't do that again. Thanks for all the ideas and help. Time for me to get serious with the fish...lol.
-Aaron

[1FASTLASER]

Fantastic bud. Also I wanna thank you for the heads up. You actually pointed out something I have never experienced but I now have it filed away in case something similar happens on a customers friends or mine boat.