Please don't kick me off the forum

[yellowtail]

In addition to my Yammie 15, I also have a Mercury 4-hp 2-stroke and, at the risk of losing my good standing with this form, I wonder if someone could suggest a cure for my troublesome Merc? I haven't found the Merc Forums very responsive.

The engine: 2016, SN-1B680388

Original problem: The engine was running rough in the mid power range, not just during acceleration. And it made little difference if the engine was warmed up. It started fine, idled fine, and smoothed out at maybe ¾ throttle and above.

Compression pegs out at 105 psi. Replaced plug, filter, carb (single mixture screw), fuel pump, tank, hose, and ran three tanks of premium gas through it. I think the fuel system is good. I seem to have good spark using a tester. Coil: Primary Winding Resistance- 00.5 ohms. Secondary Winding Resistance- 6.29 killi ohms. Used a pencil in the spark plug hole to bring the piston up to TDC. The mark on the fly wheel is about ¾ of an inch off the mark on the casing.

I replaced the new carb (about a year old), with the original carb, rebuilt with a kit.

Current problem: Engine starts with the original carb and idles for two minutes and dies.

I suspected an air leak. (I had switched the plumbing to use an external tank), but bypassing all that and running a separate fuel hose with filter directly to the fuel pump did not improve matters. Next, I cleaned the new carb (brass wire, carb cleaner, compressed air), and swapped it for the original carb.

Problem still exists: Engine starts, runs ragged a couple of minutes, then dies.

What am I missing, here? Any suggestions as to how I should proceed are much appreciated.

Bry

[boscoe99]

If you pump the primer ball continuously while the motor is started and being run, does it still die in a couple of minutes?

[99yam40]

Does it start right back up after it dies?

if not, does it have good spark at that time when it will not start?

what do you have to do to get it to start up again?

[yellowtail]

Nice to get feed back. Thanks guys. This really is the best forum and I appreciate your thoughts.

With the engine running, I was only pumping the primer ball when the revs dropped off. The fuel surged into the filter and the engine chugged back to life but only for less than a minute and eventually died regardless of squeezing the bulb, maybe after three or four minutes.

To get it started again, I pumped the bulb, fiddled with the choke and after six or eight pulls, it fired back up but the revs are uneven. When I removed the air baffle I noticed a lot of gas clinging to the face of the carb but I don't notice any blow-back through the carb when the engine is running and assumed the wetness was a result of pumping the bulb.

I used my tester and, to my uneducated eye, the spark seems to jump the gap without issue. I am able to get the engine started again, with a little work, but it won't idle at 850 rpms and I have to keep revving it, but even at that, it will finally die after a minute or two.

Thanks again... Bry

[99yam40]

Kind of sounds like you have not tried pumping the primer bulb as it is running to see if that stops it from dying.
You do not need to pump it fast or hard, just keep the carb bowl filled up.
if you think fuel comes out of the carb while you are pumping the bulb, you need to verify that and fix what is causing it.

I know nothing about that motor, but does it have a manual choke or an automatic cold starting device that might affect it like this?

[yellowtail]

The choke is manual. Typically I pull it all the way out for the first pull and then slide it to mid position for the second and third pulls. The engine used to catch on the second or third pull and I would immediately push the choke in and let the engine warm up for a minute. I have been told that most of these small engines came off the Tohatsu production line and were painted and decaled for Mercury, Johnson, Evinrude, etc. No, I didn't pump the primer bulb continuously, only when the revs dropped off. I've had the carb apart and the float level is bang-on and moves freely and the needle valve looks new. I'm curious about the ignition coil. The service manual indicates the Primary Winding as 0.02 - 0.38 Ω. I get 0.8 ohms. And the Secondary Winding should be 3000 – 4400 Ω. I get 6,290 ohms. Both the Charging Coil and The Trigger Coil check out within spec. Appreciate your input... Bry

[99yam40]

ohm reading that low can be hard to get good reading on.
did you check to see what the lead resistance was by itself?
But if it has good spark, I am not sure that is a problem unless the readings changed as it warmed up and died.

My thoughts are, you need to find out if pumping the primer keeps the carb full and motor running properly

[yellowtail]

I'm not sure how I can test the spark plug wire, it can't be disconnected from the coil. And I have no idea what resistance is acceptable. But as you say, the spark looks good, easily jumping the gap in my tester.

I've got the carb off the engine right now for another cleaning. I've cleaned the new carb and the original so many times, I'm beginning to forget which one is which! The next time I go to the city, I'll take a carb with me and see if I can get someone to ultrasonically clean it. And ask around for a small Yamaha...

I'll get back to you regarding the priming bulb.

Much thanks,

Bry

[99yam40]

the leads I talked about were the meter leads, all wire has some resistance

[yellowtail]

Question: How do you detect sugar in your gas?

[99yam40]

never heard of a test for that.
might be able to pour some into something and light it to see if a residue is left.
maybe something left of the plugs

not sure if a person could taste a sweetness compared to straight gas and I would not recommend doing that

I am sure there are places you could send a sample to have it analyzed, but do not think you would want to pay the price.

do you have someone that hates you?

[zenoahphobic]

Pour considerable amount of fuel in a large dish and let it evaporate, and then if there are any crystals formed, a bold taste test will confirm it.

[yellowtail]

I've been known to be somewhat abrasive and don't suffer fools lightly :-) Okay. Here's where I'm at... I disassembled the carb, the new one that I installed in November of 2020, and cleaned it once again. That's three times, I think. I carefully used a copper wire, carb cleaner and compressed air. I was bolting the carb back up to the engine when I thought: What was the point? I've been down this path several times before, with two different carburetors, and the results have always been the same: the engine starts, but bogs down within a couple of minutes. That started me thinking about the fuel. I use the outboard daily so the fuel in my tank is only a couple of weeks old, fresh (a relative term in the Dominican Republic), from the gas station. I emptied my tank into a bucket. The fuel looked clean and there wasn't any water at the bottom of the bucket. I poured some in a bowl and placed it in the sun to evaporate, following zenoahphobic's instructions. But as a last resort, I bought two gallons of fuel this morning and added six ounces of Shell two-stroke oil. Once in my tank, I disconnected the fuel line from the engine and purged the line with new fuel. Now the good news: The engine started and it runs! It won't idle but I've had it running continuously for thirty-minutes at about 1500 rpm. I'll shut it down, let it cool, clean the spark plug, then re-tune. With a bit of luck, I might hazard a test run up the harbor later today. Keep your fingers crossed... Bry

[yellowtail]

Good news, guys... and thank you. Took the Merc for a test drive up the harbor, it didn't sing but it didn't die either. It idled nicely but I couldn't get the maximum revs out of it. I'm hoping all it needs is an adjustment to the throttle cable. I'll fiddle with it tomorrow and report back... Bry

[yellowtail]

Did some more tweaking, looking for the sweet spot, and things have improved. Idles nicely and runs pretty steady at speed. I'm relieved.

Unfortunately, the original problem with the engine still exists. From the start, the engine runs rough: Daa-Daa-Daa- Dit-Dit-Dit- Daa-Daa-Daa...

This occurs up until at least half throttle. And not just during acceleration. The engine will not run smoothly in the low to mid range. But at this point, I'm prepared to live with it. The next time I go to the City (in search of a Yamaha E8D Enduro), I'll take my other carb with me and see if I can find someplace that will give it an ultrasonic bath.

So thank you to everyone who held my hand through this current episode. Your help, as always, is much appreciated. Happy Holidays... Bry