Motor dies when put in gear/low RPM

[AndrePSP]

While fishing over the weekend I did alot of trolling. I have a 1990 merc. 40 horse, 2 stroke, 4 cyl.
i could not keep the motor in idle or lower RPM and in gear. the best i could do was around 2.5-3 mph (per fish finder). I dont have a tach. so I dont know the RPM.
any time I tried to lightly tap it to go slower, it would just bog down and die. When starting it back up I had to get the rpms up before putting/slamming it into gear so it wouldnt die and then reduce my speed from there. it would also do this in reverse.
I cant put it in gear with out the motor bogging down and die.
I tried to reduce the oil ratio just a bit so its hotter but no help.
When I got home, I looked at the spark plugs and they looked oily/dirty.
I was also wondering if I can change the prop pitch to go slower once I get this resolved.
Please Help.

 

[daveswaves]

Re: Motor dies when put in gear/low RPM

While fishing over the weekend I did alot of trolling. I have a 1990 merc. 40 horse, 2 stroke, 4 cyl.
i could not keep the motor in idle or lower RPM and in gear. the best i could do was around 2.5-3 mph (per fish finder). I dont have a tach. so I dont know the RPM.
any time I tried to lightly tap it to go slower, it would just bog down and die. When starting it back up I had to get the rpms up before putting/slamming it into gear so it wouldnt die and then reduce my speed from there. it would also does this in reverse.
I cant put it in gear with out the motor bogging down and die.
I tried to reduce the oil ratio just a bit so its hotter but no help.
When I got home, I looked at the spark plugs and they looked oily/dirty.
I was also wondering if I can change the prop pitch to go slower once I get this resolveved.
Please Help.

It sounds like your low speed mixture is too lean, or your carbs have dirt in them. Do not mess with the oil ratio to make it run hotter, it can only lead to eventual failure. Oily dirty plugs are probably normal after extended trolling. You can certainly put a lower pitch prop on. You do not say what pitch your current prop is, you can determine the rpm from your speed if you know the pitch.

 

[AndrePSP]

Re: Motor dies when put in gear/low RPM

It sounds like your low speed mixture is too lean, or your carbs have dirt in them. Do not mess with the oil ratio to make it run hotter, it can only lead to eventual failure. Oily dirty plugs are probably normal after extended trolling. You can certainly put a lower pitch prop on. You do not say what pitch your current prop is, you can determine the rpm from your speed if you know the pitch.

I dont know what you mean my "low speed mixture is too lean" how do I fix that?
I only reduces the oil ratio tiny bit. instead of using 50:1 ratio for 5 gallons. i did it for 4.5 gallons. As I had exacttly a 5 galons tank on hand.
I dont know what pitch I have. How do I find that out?
thanks

 

[daveswaves]

Re: Motor dies when put in gear/low RPM

I dont know what you mean my "low speed mixture is too lean" how do I fix that?
I only reduces the oil ratio tiny bit. instead of using 50:1 ratio for 5 gallons. i did it for 4.5 gallons. As I had exacttly a 5 galons tank on hand.
I dont know what pitch I have. How do I find that out?
thanks

ok Andre, no problem. the pitch will be stamped right on the prop itself, it will be a long number with a dash-15, 0r17,0r19 after it. Whatever the number is after the dash is the pitch.

I will try and find a pic to post of your carbs, the low speed mixture is adjusted with a screw in the front of the carb.

 

[AndrePSP]

Re: Motor dies when put in gear/low RPM

thank you.
I looked on the prop. its aluminum. here is what was stamped on it
A40L 14P
so My guess its Pitch is 14?
also if i wanted slower speed from the prop. would I need a higher # or lower # pitch?

 

[daveswaves]

Re: Motor dies when put in gear/low RPM

thank you.
I looked on the prop. its aluminum. here is what was stamped on it
A40L 14P
so My guess its Pitch is 14?
also if i wanted slower speed from the prop. would I need a higher # or lower # pitch?

A lower number will give you a slower speed, both at idle and full throttle. A lower number will also give you a better hole shot, or take off, and be quicker to get on plane. Having said that, 14P is not overly large and should suit your 40 hp no problem. If you do mostly trolling and don,t have too far to go to get to your fishing area you could drop to a 12 P.
You could also try a trolling plate on your existing set up to try and slow you down. Any marine supply store will have one, probably cheaper than a prop and you would have the best of both worlds.

 

[AndrePSP]

Re: Motor dies when put in gear/low RPM

Thanks again. I looked into the trolling plate and it is good know and also the prop pitch is worth knowing.
I want to get the idle situation figured out first.
here is link to a carb for my model
http://www.mercruiserparts.com/Show...ng&inbr=543&bnbr=80&bdesc=CARBURETOR+ASSEMBLY

 

[daveswaves]

Re: Motor dies when put in gear/low RPM

Thanks again. I looked into the trolling plate and it is good know and also the prop pitch is worth knowing.
I want to get the idle situation figured out first.
here is link to a carb for my model
http://www.mercruiserparts.com/Show...ng&inbr=543&bnbr=80&bdesc=CARBURETOR+ASSEMBLY

Thanks Andre, I have the same pic so we are on the same page. Item 19 is your idle adjustment. I would turn it counter clockwise (left) 1/4 turraln and see if it helps your idle. Your idle RPM should be around 500 to 600 RPM in gear and around 700 in neutral.

 

[SC1650]

Re: Motor dies when put in gear/low RPM

I am guessing that you have some dirt in the carb. Even if you adjust the idle jets it may not take care of the problem. The dirt could be blocking the idle passage and causing the problem. You can try to set the idle with the jets but remember to keep them as close in adjustment as possible. Without a tachometer you will be guessing as to the idle RPM's. You may want to purchase a Merc Manual for this engine and then buy a tach (If you do not have one) so you can set the RPM's correctly. I don't know if the tach has to be outboard specific or not.

 

[AndrePSP]

Re: Motor dies when put in gear/low RPM

OK thanks guys. So whats the best way to clean a carb. carb cleaner? do i need to take the carbs out and apart?

 

[daveswaves]

Re: Motor dies when put in gear/low RPM

Andre, I suggest that you do not try to clean the carbs until you have tried the other stuff we talked about. It is difficult to troubleshoot from afar and if you take the shot gun approach it will be impossible to follow what is going on. You do not mention any other running problem, just an idle that is too low for you to troll properly and a stalling engine when you put it in gear. It is certainly possible for dirt to cause this, but you would have all sorts of other problems too. The only way to clean a carb properly is to remove it and disassemble it. Afterward you would have to do a link and sync procedure as well. Not sure you are up to that, no offense meant.

 

[AndrePSP]

Re: Motor dies when put in gear/low RPM

NO offense taken.
I just never had a boat (my first) or played with a 2 stroke, or a two stroke boat motor. so I will try to adjust the screw, and see. maybe try to use the carb cleaner for what its worth.
there really is no other problem besides the low speed trolling or having the motor die when putting in gear.
one thing. when we where trolling and had tail wind. the fumes from the exhaust were strong enough where I got a head ache and had to start zig zaging accross so I wouldnt get that direct wind and fumes.
SO, it kinds sounds like its running to lean.
I wouldnt mind getting a new tach. just to watch the RPMs. do I need a specific merc tach or any tach with merc wiring?

 

[daveswaves]

Re: Motor dies when put in gear/low RPM

NO offense taken.
I just never had a boat (my first) or played with a 2 stroke, or a two stroke boat motor. so I will try to adjust the screw, and see. maybe try to use the carb cleaner for what its worth.
there really is no other problem besides the low speed trolling or having the motor die when putting in gear.
one thing. when we where trolling and had tail wind. the fumes from the exhaust were strong enough where I got a head ache and had to start zig zaging accross so I wouldnt get that direct wind and fumes.
SO, it kinds sounds like its running to lean.
I wouldnt mind getting a new tach. just to watch the RPMs. do I need a specific merc tach or any tach with merc wiring?

Any marine tachometer will work with your engine, there will be directions inside that tell you how to set the tach for your engine.
Unfortunately, trolling down wind with a 2 stroke can bring tears to your eyes. It does keep the mosquitoes away though!

 

[milehighboater]

Re: Motor dies when put in gear/low RPM

Hey, S-curves are good for trolling anyway.

 

[AndrePSP]

Re: Motor dies when put in gear/low RPM

Thats true milehigh. kind of a long narrow lake and was busy that weekend where it made it hard to do big S curves.
Anyways
I've been busy and have not yet tried to adjust the idle screw.
I also oreder a tach. and got a service manual.
Earlier I wrote how my spark plugs were oily.
here is what the manual says about wet fauling.
A. Spark plug heat range is too cold.
B. Prolonged trolling.
C. Low speed cabrurretor adjustment too rich.
D. Improper fuelil ratio.
E. Induction manifold bleed off passage obstucted.
F. Worn or defective breaker points.

My Q.
what does A mean and how to fix it?
this says too rich while we have been talking about too lean... which one.
what/where is induction manifold?
what are breaker points?

 

[ClassyGlassy]

Re: Motor dies when put in gear/low RPM

the heat range of your plug is the number, ie: L76V is a 76 heat range. To go up in heat range you would go up to a L77V and down would be a L75V if they're available.

that says too "rich" referring to your wet plugs, whereas the others have been describing a too "lean" situation where your engine is starving for fuel when you try to take off from idle.

you got me on the breaker points.........

Your wet plugs are from B stating prolonged trolling. You don't need hotter plugs!

 

[AndrePSP]

Re: Motor dies when put in gear/low RPM

Thanks classy.
I dont have the tach yet to tell my RPMs and I want to go fishing tomorrow so I played with the idle adjustment. seemed fine.
kind of sucks is I have two carbs and it is hard to tell whcih carb is acting up. So i turned both screws 1/4 turn counter clock wise, turned it off and on few times but i think i will have to be in water under load to see what happends.
anything special about tuning dual carb motor?
dave you were asking me if anything else is going on.
There is a gas leak from top carb where it has the throttle shaft going to the lower carb. I guess there is no way to fix it as there are no seals/gaskets. or is there?
I also noticed an oil leak from the gear housing under the prop. It doesnt look like gear oil but more like regular oil. not sure from where or if its just exhaust residue of the 2 stroke.

 

[AndrePSP]

Re: Motor dies when put in gear/low RPM

do i need to have the carbs adjusted differently when fishing in high eleveation? motor worked fine at home after adjusting the screw..
when i was on the lake I had hard time with it. I think the lake is 6750 ft elevation while i am at 200.

 

[ClassyGlassy]

Re: Motor dies when put in gear/low RPM

with that kind of elevation change your carbs should be overly rich at the lake if they are set right at sea level! Different jets are needed for optimal performance with that kind of elevation change.

But being "Fat" or "Rich" at high elevation shouldn't cause you to die when giving throttle like when you are "Skinny" or "Lean".......you'll just smoke a little more up at the lake due to the excessive fuel mixture and it can cause wet fouled plugs too, especially when over trolling!

 

[AndrePSP]

Re: Motor dies when put in gear/low RPM

I just dont know whats going on with this motor. what about the oil leak from prop housing?
Also, what should my top speed be with this motor?