Older 2-stroke behavior?is this normal?

[Ghostrider1977]

(1980?s Merc 2-stroke, Outboard: 9385696)

This is my first boat and I have some questions as to how the engine runs.

Essentially, the outboard needs to be started with throttle applied (in neutral) to get it running. It will not start in the idle position. After its started, it will not idle for more than a minute without bogging down and stalling. I have to give it some throttle every now and then to keep it running at idle speed.

Another thing is that to get it moving, I need to rev it up in neutral and then quickly throttle back, click it in gear and throttle forward quickly, else it stalls. If I just click it into gear and slowly apply throttle it stalls.

Once it gets going, it seems fine up to top speed. I can slow down to a moderate clip, but it still wants to stall at slower speeds.

The plugs are clean. The carb was looked at by a mechanic and appeared clean. I was advised that older 2-strokes can be finicky and I need to learn how to manage the engine, and I?ll get used to it. (i.e. if it runs, leave it alone.)

Any ideas what else could be wrong or were else I should start looking? Or, is this normal behavior for an older outboard?

 

[chief huntum]

Re: Older 2-stroke behavior?is this normal?

I have the exact same issue with my 1984 25hp Merc. Unfortunately nothing I tried or a dealer tried could help it. It runs good, but stalls bringing it back to neutral unless I bring it down real easy. Same with starting. I have to bring to neutral and engage the throttle before the rpm drop. Sorry I couldn't be of more help. Mine started when the engine overheated after not noticing water coming from the pee hole. Maybe your's overheated at some point too.

 

[acarver81]

Re: Older 2-stroke behavior?is this normal?

Not sure if its normal, but it is a pain in the butt. I have a late 80s 9.9hp merc that is doing essentially the same thing. I got my neighbor (a diesel mechanic) to come over and look at it, and he found that the butterfly wasnt opening untill the throttle was almost halfway up. We adjusted the armature linkage on the side of the motor and he adjusted the fuel mixture screw. I had it getting way too much fuel. When that didnt get rid of all the idle/going into gear problems, I started looking at the fuel lines. I had to replace the fuel filter because it wasnt staying in place and the fuel bowl gasket was broke, allowing air to get sucked in. When THAT didnt work, I replaced the fuel tank, hose and fitting. But the fitting wasnt the right one, so I had to use the old fitting. That was when I found the crack in the fitting, More air getting into the line. Short story long, check the fuel system for cracks, worn out hoses etc. And watch the butterfly to see if it starts to open when you start to open it up, if not, lengthen the armature linkage untill it opens as soon as you open the throttle. You can find schematic drawings of this on the Mercury website. Also, add fuel stabilizer to every tank, these older two strokes werent made for this and I have been told to do this as well. I have also found that mid or high octane fuel helps some too.

 

[Ghostrider1977]

Re: Older 2-stroke behavior?is this normal?

Not sure if its normal, but it is a pain in the butt. I have a late 80s 9.9hp merc that is doing essentially the same thing. I got my neighbor (a diesel mechanic) to come over and look at it, and he found that the butterfly wasnt opening untill the throttle was almost halfway up. We adjusted the armature linkage on the side of the motor and he adjusted the fuel mixture screw. I had it getting way too much fuel. When that didnt get rid of all the idle/going into gear problems, I started looking at the fuel lines. I had to replace the fuel filter because it wasnt staying in place and the fuel bowl gasket was broke, allowing air to get sucked in. When THAT didnt work, I replaced the fuel tank, hose and fitting. But the fitting wasnt the right one, so I had to use the old fitting. That was when I found the crack in the fitting, More air getting into the line. Short story long, check the fuel system for cracks, worn out hoses etc. And watch the butterfly to see if it starts to open when you start to open it up, if not, lengthen the armature linkage untill it opens as soon as you open the throttle. You can find schematic drawings of this on the Mercury website. Also, add fuel stabilizer to every tank, these older two strokes werent made for this and I have been told to do this as well. I have also found that mid or high octane fuel helps some too.

So was it finally a crack in the fitting that was the culprit?

 

[Ghostrider1977]

Re: Older 2-stroke behavior?is this normal?

^bump

 

[Silvertip]

Re: Older 2-stroke behavior?is this normal?

Most carbureted two stroke engines and do indeed to be have a faster idle during warm up. That is why the fast idle feature (either a separate lever on the control box or a neutral idle feature on flush mount control boxes) is incorporated. The current EFI/DFI engines (2 o 4 stroke) all do this automatically so fast idle is not unique to 2 strokes. All of the above posts are very likely carburetor rebuild candidates followed by a complete link & sync. Continue to run lean fuel mixtures and you will later be looking for advice on an engine rebuild.

 

[ifixf18s]

Re: Older 2-stroke behavior?is this normal?

Does it have a Primer/idle speed knob? this is a thread that i answered the other day with a guy having idle problems.
I'm new to boat engines and I have just got myself a pontoon boat with a 1988 Mercury 25 hp outboard (electric starter).
What I need to know is what exactly does the black knob on the front left of the cowling actually do?...some people say its the choke...others say its the idle setting for trolling...or is it both.
If someone could explain to me in plain english how to set this knob for starting it would be appreciated.
At the moment I just pull it right out to start the motor, then push it half way in and let the motor run for a minute, then all the way in as I leave the dock and pick up speed, that works fine but it stalls when I stop so IS the knob a idle setting too and should I be turning that too as the engine warms up?
This was my response; UK bob, I have a 1996 25HP tracker outboard by mercury marine. Here is what my operators manual says for hand tiller models. not sure if thats what you have but this may help. These are the steps for starting the motor that deal with your mystery knob. 1). Turn Primer/idel speed knob full clockwise to increase engine idle speed for starting. 2). When engine is cold, pull out and push in the primer/idle speed knob 1 to 3 times to prime the engine. Leave the knob in the pulled out position when starting. 3). Push in the primer/idle speed knob after engine starts. If the engine begins to stall re-prime untill engine is running smoothly. 4). Turn the primer/idle speed knob counterclockwise to obtain desired idle speed as the engine warms up. Keep in mind these steps i listed are only the steps that talk about the primer/idle knob. i did take it verbatum out of my manual.

 

[acarver81]

Re: Older 2-stroke behavior?is this normal?

So was it finally a crack in the fitting that was the culprit?

Not really, although it did help some. I have run out of ideas and am taking it to the shop. Will let you know what they say it is. My opinion is that it needs a carb rebuild.

 

[backyard mechanic]

Re: Older 2-stroke behavior?is this normal?

Older engines need to have a little throttle to keep the motor running while warming up. After a few minutes you should be good to go.
The biggest problem I've found with these older engines is they are not set up correctly. Time after time I ask the question about syncronization and the answer is "I don't know" or "well I just had it to the shop, I assume it is". "Assumption" is not reality and many "good" shop mechanics fail to check the compression and syncronization on every shop visit. If already set up right that process takes less than a half hour. Still, they will begin with turning screws only to find after an hour or more they find a bad cylinder or a bad lower unit. It happens a lot and that's sad.
Carburetor syncronization and ignition timing are critical to how the engine performs. To "screw" with the settings is to cause a problem and if there's a screw to turn it will be turned.
Simply stated, If the engine doesn't idle there is a problem and that will need to be diagnosed and fixed. A manual will help with carb settings, ignition timing and the syncronization of the two. Learning to do all that yourself will save you hundreds of bucks. A manual costs about $30. You decide...

 

[acarver81]

Re: Older 2-stroke behavior?is this normal?

Well, after taking my motor to the shop, it turns out that I did actually fix the fuel problems by replacing all that I did, but it didnt cure the running problem. The mechanic found that the ignition switch box was the culprit. It was running fine for a few minutes there, then dropped a cylinder and was only running on one. after a few diagnostic checks, he found it. Not sure if that is what is wrong with yours, but if you start it and let it run for a couple minutes, feel the side of the cylinder head, if one half is hotter than the other, that could be your issue as well. I have checked around and the Mercury part is a little over $200, but look on ebay. Manns outdoor has an ebay store with aftermarket parts at about half the price. For me, it was well worth the half hour labor fee to find the true problem, a few minor adjustments and alot of free advice. Good luck!

 

[sschefer]

Re: Older 2-stroke behavior?is this normal?

Here's what I know. Merc recommends increasing the jet size by .002 when rebuilding the carbs. You also want to decrease WOT advance by 2 degrees. This is to accomodate today's fuels. It made a world of difference in my 100hp Mariners idle during warm up. The decrease in WOT timing helps with detonation problems and both help the engine run cooler.

 

[Ghostrider1977]

Re: Older 2-stroke behavior?is this normal?

Does it matter if the engine is in the water or just running with muffs?

I ask, becuase I found a cracked, leaking, fuel line going to the carb. I had both lines replaced at the shop. The mechanic also checked the compression and said it was fine. The shop said the engine idled great after they changed the lines.

But, after taking it out on the water today, the same behavior persisted. What condition could change depending on running with muffs, or in the water?

 

[turbinedoctor]

Re: Older 2-stroke behavior?is this normal?

Does it matter if the engine is in the water or just running with muffs?

I ask, becuase I found a cracked, leaking, fuel line going to the carb. I had both lines replaced at the shop. The mechanic also checked the compression and said it was fine. The shop said the engine idled great after they changed the lines.

But, after taking it out on the water today, the same behavior persisted. What condition could change depending on running with muffs, or in the water?

The change in running on muffs and in the water would be back pressure on the exhaust. On the muffs it will run leaner and probably idle fine. What HP is your engine? Mine is a 90 and have an enrichener valve for cold starts. The enrichener has a stem on top that can be turned if the soleniod stops working. If that stem is not closed all the way it can let fuel into the crank case and cause flooding problems at lower rpm's.

 

[Ghostrider1977]

Re: Older 2-stroke behavior?is this normal?

It's an 18hp. I do have a knob in front, that operates a plunger that is pressing on what I think is some sort of rubber diaphragm. I assume its the choke mechanism...because when I push the key in (to engage the electric choke) the solenoid engages the same mechanism and pushes it down.

(According to my manual, this diaphragm is the "enrichment valve".)

Here is what it looks like:

Choke off:

Knob turned, Choke on:

It starts without the choke, as long as I give it some revs, in nuetral, just as it starts to fire up. Whenever I try to use the choke, it seems to flood the engine and it never starts. I have to use the afore mentioned method.

EDIT: after thinking about this for a while, I notice there are three settings on that knob. Completely off / partially touching the diaphragm / and all the way down. (all the way down is what happens with the electric choke on the ignition key) Now, I've been running the engine with it completely disengaged. (Like in the first pic.) BUT, I was looking in my manual for the idle SPEED screw, and I noticed that all that screw does is adjust the stop for this plunger.

Here's the catch. I've been running the engine with this plunger completely disengaged, same as first pic. In other words, the idle speed stop screw is also disengaged!

It's only when the knob is set to the "partially touching diaphragm" setting would the idle stop screw adjust how "partially" this thing is pushing on the diaphragm. So, adjusting the idle speed screw (with the knob in this position) looks like it fine tunes how far this plunger is pressing down on the enrichment valve.

Could all of this behavior been caused by me running this way?

But, I have another observation that might help...or hurt. I took the advice and squeezed the fuel bulb a few times. After a few squeezes, fuel starts coming out of the carb AND a small hole in the carb body that looks like a screw or plug should be there?! OMG! Am I missing a part???

Question #1. Should squeezing the bulb a few times cause this much fuel to come out of the carb in these places? It did take a few a squeezes to do this...maybe it's just overflowing up from the fuel bowl???

Question #2. Am I missing a screw or plug, or is this opening supposed to be there? (also note the fuel coming from the hole.) (It doesn't look like anything is supposed to be there, from my manual...)

Question #3. Are my assumptions on the idle stop screw knob settings correct, and my probs are due to this? Could the enrichment valve being completely off, play a role in this behavior?

 

[coolguy147]

Re: Older 2-stroke behavior?is this normal?

yup neeed a carb rebuild and clean


and adjust proper float level cause its overflowing

 

[Ghostrider1977]

Re: Older 2-stroke behavior?is this normal?

So...squeezing the bulb, a few times, rather hard, should not result in any fuel coming up?

Just trying to get a feel for how much, if any, is too much, given that the bulb is pushing fuel, under pressure, into the system. I'm not an expert, but I would expect some leakage. No?

 

[turbinedoctor]

Re: Older 2-stroke behavior?is this normal?

It appears you may have found the problem. A bad seat and valve in the carb. You should not get any fuel out of the bowl with a good one hand squeeze on the primer bulb. Also check the float setting, it could be out of adjustment. If it has been awhile since the last carb job, go ahead and do one making sure to adjust the float correctly.

One more way to check is to prime the carb then disconnect the fuel line and start it to see if it runs better.

 

[j_martin]

Re: Older 2-stroke behavior?is this normal?

Note: The carb needle valve can stand about 7 PSI of fuel pressure. A ham handed white knuckle grip on the primer bulb can develop 10 PSI or more.

If the carb is empty, you should feel fuel being pumped, and then a hard stop when the float bowl gets full. A little harder squeeze shouldn't overcome the needle valve. A white knuckle squeeze will overcome it.

Takes a little moxy, I guess.
hope it helps
John

 

[Ghostrider1977]

Re: Older 2-stroke behavior?is this normal?

I'm certainly not white knuckling or gritting my teeth on the squeeze. I would describe it as more like a firm & steady squeeze after the bulb fills up, when the fuel starts coming out of the carburetor.

Another way to try and describe the pressure is that I can make it overflow with a hard squeeze from just my thumb and forefinger on the bulb...(I realize this is all subjective and hard to describe over a forum post.)

From all the posts?it seems like the general consensus is that there is some sort of leak in or near the carburetor that is causing the engine to bog down and stall at idle or low speed. I'll probably have it taken to the shop again to breakdown the carb for bad seals or a leaking fuel pump or fuel enrichment diaphragm. (I know, I know?I should learn to do it myself, but I simply don?t have the time. I barley have time to fish! So, I?d rather pay a wrench for my time.)

If anyone else has any other ideas or tips, please feel free to chime in. You all have been a great help!

 

[sschefer]

Re: Older 2-stroke behavior?is this normal?

As was said before, (not by me), get a carb kit and a needle/seat kit, get a new jet .002 over stock (if you can find one). Rebuild the carb and you should be good to go. It's not as difficult as it looks. Just lay everything out in the order that you take them apart and take pictures even if you think you'll remember, (trust me, you won't). I would order a new float also just in case you have the old style non-E-10 rated float.

As a side note: You may see parts that need replacing that are not in the kit. Identify them all first then order and replace them too or you will be sorry you didn't. It is not uncommon for these 1 day jobs to extend into 1 month projects because of parts ordering. The end result is extremely rewarding so hang in there.