1977 140hp Evinrude trouble

OK, be patient, I'm new at this. So, I bought a beautiful 1978 Stinger Bass boat about 10 years ago. Other than replacing the fuel pump, it has never given me any trouble. Last fall, I was leaving one spot on the lake and going to another one, so, I opened the throttle all the way just to clean her out a bit. After about a 1/4 mile, it just shut off, just like you had turned the switch off. It started right back but would not take fuel enough to get the boat going more than just a idle speed. If you tried to push the throttle, it would choke and puke then shut off again. My brother worked the controls while I manually worked the carb, after a few tries, I got the boat back up and going, even back up a plane. So, that's where the problem started. Here's everything that has been done to the motor and now, it's worse than when it started. Just so you know, runs perfect on muffs but as soon as you drop it in the water, it idles but rough but will not take fuel, just shuts off but starts back. Now, if I even touch the carb throttle manually, it shuts off, no spitter or sputter, just shuts off. Here's the long list that has been done to the boat. 3 different mechanics and the last one, well, he just said to come and get it, he can't figure it out and he spent a lot of time on the motor and took it to the lake 5 times but can't figure out why it's shutting off. New fuel pump, all lines replaced, fuel tank checked with nothing wrong, new plugs, carbs have been cleaned and checked by 2 certified mechanics, nothing wrong with them, new power pak, new timing plate, new stator, replaced fuel pump with electric fuel pump, new recitifier, new crankshaft seal, timing rechecked and adjusted, all linkages checked and adjusted. After getting the boat back, I removed the lower unit just to check to make sure the exhaust wasn't clogged or any obstructions. That was the lower part only, nothing in the upper part was checked. I am a ASE certified mechanic but not on boat motors. If anyone has come across this problem, I sure would appreciate some help. I don't want to take it back to another mechanic who spends countless hours then charges me another $1,000 plus dollars to say, I don't know what's wrong with it. The boat is a 78 but the motor is a 77 140 Evinrude. I'll try to figure out how to post pics if I can but it's just a beautiful boat and I'd love to get it back on the water. Anyone, please, help me...LOL
Compression check has been done by 2 different mechanics, both amazed by the strong readings for it's age, nothing wrong with compression. This motor hasn't been run enough to even burn off one spec of paint and always been garage kept by me and the previous owner.

Well----" strong readings " --- means nothing.----What are the actual compression numbers.-----And does spark jump a gap of 7/16" or more on the 4 leads.-----Sorry ----But i think it only sounds good to you on the muffs !!----It is not running " perfect " as you say.-------Check the wiring and the ignition switch in the control box.-----Your location ?

racerone said:

Well----" strong readings " --- means nothing.----What are the actual compression numbers.-----And does spark jump a gap of 7/16" or more on the 4 leads.-----Sorry ----But i think it only sounds good to you on the muffs !!----It is not running " perfect " as you say.-------Check the wiring and the ignition switch in the control box.-----Your location ?

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As I was saying, it happened last fall, October I think. The compression readings were told to me and I can't remember them...LOL. The reason I said strong was because all the cylinders were within 5 psi of the strongest variation of what they should read. The 2nd time was in December and that mechanic told me the same thing. All 3 pretty much insured me there wasn't nothing wrong with the compression in the motor. I just wanted to rule that out for any response. It has been checked. Your correct about it running on the muffs but it's obvious the engine is so much smoother on the muffs than in the water, as far as running well on the muffs, I'm not saying at higher rpms but it will not adle smooth at all once you drop the boat in the water. Spark on the plugs has also been verified, I think buying a new power pak was just a guess by the 1st mechanic. Well, it's all been a guess because no one can tell me what causes it to do that. I've thought it's air fuel problem from the start but as I said, I'm not a boat motor mechanic. However, symptoms with bad running engines are not that different as far as internal problems but certainly not the same with the componants that controls the running of the engine. I'm just asking but I noticed there is nothing electrical around any parts of this carb, yet, all I have to do is manually try to manipulate the butterflies on the carbs and the engine dies emediately. I'm in Bristol Tn. Thanks for replying and I'm open for any help, but when a 30 year mechanic says he gives up and has no idea what's causing it to do this, it's pretty discouraging. I've spent around $1600 since the problem started, yet no closer to fixing the problem. I just don't want to take it to another mechanic to guess at problems and cost me more money and my boat still not running. At some point if I can't figure it out, one must cut his losses and move on but I really hate to give up on the motor since I've replaced so many parts...thanks...Danny

This motor uses the flat end spark plugs not the gap type plugs....Danny

Sorry, I see what you mean on the plug leads not the plugs. All I know is that all 3 have said the firing on the motor to the coils and plugs is good.

2 out of 3 of these mechanics work for local Marine boat repairs in my area. I don't have but 1 more to choose from if I take it to someone. The first mechanic owns a small engine shop and he does work on any 2 stroke engines. I've used him many times for other things and he's always fixed them for me. I chose him first because he's old school and so is my motor.

Sparkplugs are not used to determine the health of the system !!---Use a test device.-----I think this would be simple to diagnose but you are 1000 miles away !----Your motor needs 4 things to run.-----Spark at the right time .----Cylinder compression.----Correct amount of fuel ( too much is no good ) ----And the elusive crankcase compression.------I would remove the 4 bypass covers on the side of the block.----Six small bolts each cover.-----Allows you to look at pistons / rings.----Just 4 new gaskets at $2 each or so.-----Perhaps a reed valve issue.----Or a crankshaft seal ring or oil seal issue.----Sad that your local shops can't help you for reasonable coins.-------But that is why some shops do not take on work on older motors.

The crankshaft seal has been replaced. I assume, since the compression test were good, none of them went any deeper into the motor such as the reeds. Can't say your not correct but can't imagine the compression would be correct if it was the reed valves? If this was a 350 chevy engine and I tried to manipulate the carb by hand and it done this, I'd be looking for a intake manifold leak somewhere because it would tell me it's sucking too much air when you try to apply more fuel. Wouldn't be uncommon at all for it to idle perfect, even with a leak. These guys have worked on motors for me for years, blew my mind when none of them seem to have a clue why it's acting this way. I guess what's got me confused is that the symptoms I started with....shutting off after running it wide open for a 1/4 mile, is not the symptoms I now have. This motor wouldn't run wide open no matter what I tried to do, it simply won't take another drop of fuel without shutting off. I can't do it manually and as soon as you drop it in gear to go, it dies, either way, it won't take anymore fuel. I do appreciate your input my friend. Is there any other place besides the crankcase seal the motor could be sucking air? Danny

The 2nd mechanic installed the new timing base plate, set the timing but the 3rd one confirmed the timing when he also checked it.

Sorry----But the reed valves have nothing to do with compression in the cylinders !!

What do they do sir, just trying to understand the process of these engines, maybe it will make some sense to me as to what's going on...thanks...Danny

Parts for this motor have been hard to find. From doing some research, there are many things on this 77 that was only done this one year. I know my timing base plate had to be for this 77, nothing before or after would work on the motor. Not sure how this come about but the 78 and up is a different motor than mine. At least many parts are different.

Reed valves have to do with compression in the CRANKCASE.-----When intake and exhaust ports close then compression in the cylinder starts.----The reed valves are nowhere in the picture,

When I remove the side plates, what am I looking for that indicates the reed valves are the problem? Thanks again for your help...Danny

You want to look at the pistons and rings !!

Looking for any broken ones I assume...Danny

In a two stroke engine, the reed valves create compression in the crank case on the down stroke of the piston to force the fuel/air/lubrication mixture into the combustion chamber when the piston reaches the intake port.

By any chance have you checked for any wires that could be rubbing on the timer base when it moves?
A sudden shutdown like that suggests to me the engine kill wire shorting to ground...

Danny, I don't know what is wrong with your motor, but something you said got my attention. You said that dinking with the carb throttles would make it die. That is normal and leading you off in the wrong direction. You need to understand that the spark advance has to happen BEFORE the carbs open more than just a bit. If the spark advance lags behind the carb throttles, it will stumble and maybe conk out. Put simply, it's called link & sync by most of us. and it has to be correct and by the book..

Try a different power pack on it !

Thanks to all of you for trying to help me figure this out.
1st, when I manually manipulate the carb butterflies, I hear a sudden rush of air, the moment I crack open the butterflies. To me, it's not killing the engine like a loss of fire, it's like when you prime a carb on a 350 trying to get the fuel pump to pull the fuel from the tank or when it uses all the fuel you poured in and it runs out of fuel. If I barely open the butterflies and it starts to die, if I release what I'm doing, it will spitter and sputter and go back to idling. So, that tells me it's not something electrical killing the motor, undestand this, I'm talking about a 1/16 of a inch trying to open the carb and if you continue, it kills the motor instantly but it will start right back.
2nd, I forgot to mention this but when the power pak didn't solve the problem, the 1st mechanic got the supply place he bought it from to exchange it for another one. So, it has had 2 power paks installed.
The timer base plate I bought wasn't the old style, it was a MDI or TPI timer base plate, can't recall which, I think MDI, one of the blue timer base plates. It was installed by the 1st mechanic. Neither of the next 2 mechanics said anything to me about the new style timer base plate and both of them has confirmed that the timing is set and right on the motor.
When I manually manipulate the carb, it does not seem to matter if the motor is in gear or not. The entire fuel system has either been replaced and at least checked and nothing there helped at all. I took my fuel line off my tank and used a 2 gallon jug to check the tank, stem or a clog in it but it didn't help anything.

The last mechanic installed a electric fuel pump and it made no difference.

The carbs have been removed, cleaned and checked by 2 different places. Both mechanics sent the carbs to whoever they use to work on carbs. So, the carbs have been checked by 2 people other than any of these 3 mechanics that worked on the motor.

This last guy, David, that worked on the boat is the largest boat repair shop in my area. He has 5 employees and has been in business for over 35 years. I'm not sure what I can figure out that he can't. Imagine this, he docked 27 hours he has worked on this engine, had it on the lake 5 times and just got to the point to say, I can't spend anymore time on it with all the other work I need to do. He told me if I wanted to, I could bring it back in October or November when he was caught up and he would try again. He didn't charge me anything for the labor, stator, electric fuel pump or crank seal he installed. He was mad at himself because he couldn't fix it but I'm sure he was upset for all the time he worked on it but really couldn't charge me for labor since he didn't fix the problem. He's a really good guy but I'm not sure what I can do that he couldn't.

Can anyone tell me how to post pics on here. I think if you see the boat, you will understand why I don't want to give up on it.

I guess the reason I'm posting on hear is just hoping I come across someone who has had this same situation and finally figured it out. Before I came on here, I done hours of research trying to find the same situation, found many similiar but none the same. All the ones with similiar problems, these mechanics have already eliminated the possibilities that fixed all these other motors. The only thing I can say I haven't heard any of them say they checked are those reed valves. If that causes these symptoms, one has to wonder why none of them checked those reed valves.

For 25 years I worked for ITT, the company that developed the OBDII system in your car. I was a trouble shooter for every manufacturer. When a dealership couldn't figure out why the check engine light was on or what was causing the symptoms it was doing, they called us in. I've been down this road on automobiles, when so many good mechanics have tried to fix a problem and can't, it always seemed to turn out to be something so simple that we all tend to overlook. Or, it's just one of those things you can't explain why this part had anything to do with this part and caused the problem but, it did. Between the 3 mechanics who have worked on this motor, were talking close to 90 years of experience, all 3 to me are simply not thinking outside the box of what might cause this that maybe has never caused a motor to act this way. I had a $40,000 snap on tools scanner in my hands and sometimes, it didn't help at all. I just had to think outside the box, stop relying on technology or my experience and usually, I would figure it out but like I said, I'm not a boat, weed eater, lawnmower etc. motor guy. I can take a v8 engine apart and put it back together in my sleep but honestly, I just don't understand these engines other than the combustion, internal parts that are really the same no matter the engine. Controlled explosion inside a cylinder, hasn't changed since the first combustion engine was made. many improvements but the same concept.

That timing base plate is made by CDI. Maybe this will help some. When the fuel pump, spark plugs and power pak were replaced, it didn't change the motor any but I could still manipulate the carb to get the motor to run, it didn't kill the motor like it does now. Once the timing base plate was changed, the symptoms changed, after that, you even touch the carb and the engine died. I read many reviews on the CDI timing base plate and no one had anything negative to say about it. I was concerned because it doesn't look anything like the OEM that was on the motor and none of the mechanics have pointed a finger at it to say, it could be the cause. I just know, after replacing it, the problem got worse or at least changed what the motor was doing. If you think about it, I could have had the problem for a while since I seldom run this motor wide open. I'm usually going in before daylight and with logs and other things on the lake, I just ease along to the spot I want to fish. When I move, it's usually not far from where I am so there's really never a point I feel the need to run it wide open, I was just sorta cleaning things out that day. Anyway, that doesn't seem to be near as serious as the problem now, I can't get above idle without the engine shutting off.

It might help to think of these two stroke engines as a collection of one cylinder engines.
Each cylinder has it's own carb throat, it's own reed valve, it's own little section of the crank case
and so on. There aren't too many thinks that will take out all of the cylinders at once. The top carb does
the top two cylinders, the bottom, the bottom cylinders. Ignition is split left and right.
The fuel pump is common to all carbs. At idle, engine RPM is more a function of timing that throttle.
These engines use a mechanical MAP where a modern engine uses a computer to manage the MAP.
You have to advance the timing and butterflies together and in the right amount. That's what the "link and sync"
process is about. Put a timing light on it and watch to see if the ignition dies when the engine cuts out.
You said the problem started all at once. This is what makes me think this is one item that affects all cylinders
at once. You will find it. It's just going to take some detective work.

I still think you need to go over the wiring carefully and look for a wire
with damaged insulation.