a few tuning questions

[jeff_smith_0423]

Evening...

So, a few have followed my "back to life" saga with my Merc850. Tonight I hauled the rig out of the garage and fired it up again. My goal - achieve operating temperature and allow to idle for a period of time. I wanted to get about 20 minutes of consistent run time. Why so long? The closest body of water is 35 minutes away, is known as an "unfriendly" lake, and i would really like to get a little bit of confidence with the motor before I put the boat in the water.

So, it's about 40 degrees out here tonight. Haul out the rig, hook up the flush muffs, and it's alive and idling after three cranking cycles and a healthy dose of choke - i expect these motors to be cold blooded and that isn't alarming.

I allowed it to run for a bit, shut it down, restarted with a half second of cranking. Allowed to run at idle for about another 15 minutes with no issues, and then it just stopped cold. Not froze up, no sputtering, just stopped.

When i went to restart, i checked the primer and it was still solid. With a LOT of cranking and choke, i was able to get it restarted, but had to give it a lot more throttle to keep running. I would say that the throttle and timing arms were moved at least 3/4 of an inch off of their stops. Throttling down causes it to stall instantly.

So. Is it possible that it actually took 20 minutes to come up to operating temp and my idle setting is just that far off? My idle mixture screws are set at about 2 and a quarter turns out. Was hoping to do the final adjust once it was in water.

I have NOT done the sync & link procedure, as I have no way to mount the motor in a test tank, and i don't have a body of water i can get out on to do it underway. However, the P/O appeared to have been a relatively conscientious maintainer, and i don't have any real reason to think they're terribly off. Especially after how well it seemed to run when cold.

Ok.. that was long. And rambling.. and might not make any sense. I don't have any idea what could be causing this problem. It got dark and I had to put it away so i couldn't restart after it cooled to see if the problem only happens when warm.

 

[achris]

Re: a few tuning questions

Next time it does that, immediately pull the plugs and have a look at them. Plugs are the windows to the soul as far as engines go. I believe that not enough people 'read' spark plugs. What you're looking for is a nice even slightly oily finish if they are reasonably new or some oily carbon build up if they are a bit older. What you really don't want to see is a really nice clean fresh-looking plug. That would indicate water is getting into the cylinder and steam cleaning the plug. I have have so many people say that they thought there was nothing wrong with their engine because the plugs are always so clean. WRONG!!!. That's when they have come in for a re-build/new engine. That's the other thing, keep your plugs in order, so you know what came out of which hole.

Chris............

 

[Chris1956]

Re: a few tuning questions

Jeff, I will assume that your motor is an inline 4 merc from the seventies, with two side bowl carbs. If so, normal initial idle mixture setting is 1-1/2 turns out from lightly seated. Since your settings were 2+ turns out, it is likely the motor loaded up at idle, hence the need to advance the throttle.

BTW - Since that motor doesn't have a thermostat, it usually does not warm up on a flusher. It needs to have a load on it in order to warm up. Check the water expelled while running on the flusher. it will normally be lukewarm at most.

To set the carbs properly requires you use the lake or a test tank. I normally set the carbs to give the smoothest idle possible, with the boat in the water and in neutral, or preferably in forward gear. At this setting the idle mixture is too lean to allow the motor to accelerate, so you need to open the top carb 1/8 turn and try to accelerate. In it accelerates sommthly you are done. Most likely you will then need to open the bottom carb 1/8 turn and try again. Repeat the acceleration test and the top to bottom sequence of richening the mixture 1/8 turn at a time. Eventually you will find the best compromise setting between lousy idle and good acceleration, and good idle and lousy acceleration.

 

[jeff_smith_0423]

Re: a few tuning questions

It's a 1977 inline 4. Has two square bowl carbs. The Seloc manual and mercury owner's manual both specified two turns out from seated. I went a little rich just to protect from a lean burn situation.

The water in fact, was barely lukewarm.

This "water intrusion" problem is what worries me. After my first run, i did read the plugs. 1 was crapped up, 2 less so, 3 clean, 4 sparkling. I attributed #1 being old carbon/oil in the bore. Cleaned the plug hole out with a rag, and #1 and #2 ran about as clean as #3. I attributed #3 and #4 cleanliness to a lean burn, so i richened up that carb about an eighth of a turn.

I pulled the plugs last night after about and hour of cool down and found them to all to be in the same condition. Slighly damp with gasoline, and with a drop of unburned oil at the bottom.

If i have time tonight, i'll see if i can duplicate the problem. Maybe it's just fuel starvation. Either way the thought of having to replace corroded water jacket gaskets would probably make me abandon the project :s

 

[Chris1956]

Re: a few tuning questions

Jeff, If the motor has seen saltwater, the possibility of corroded exhaust covers is high. However, the lower crank seals can also go bad, allowing water into the crankcase. These are easy to change, after you pull the powerhead. You can loosen the closest chrancase bolts, and then the end cap will come off. You can fit three seals in the lower end cap, althought the manual specifies ony two.

I do not know why your manual specifies 2 turns out, on the idle mixture. Experience indicates that 1-1/2 turns is too rich, and I end up setting them just about ~1-1/4 turn out.

A lean idle mixture will not harm the motor BTW. Alternatively, if the high speed jets are clogged the resulting lean mixture at high speed is very bad.

 

[jeff_smith_0423]

Re: a few tuning questions

I could be wrong. I may have done one and a half, then opened it up another quarter. I'd have to reset them to verify.

I was told that a lean burn condition would easily smoke a piston, hence the caution with the richness.

Motor has never been in saltwater, or out of central indiana, for that matter.

Pulling the powerhead just gives me the willies. Of course, so does scrapping the engine and looking for another one that i'll probably have the same problem with.

 

[jeff_smith_0423]

Re: a few tuning questions

And after checking the handy seloc online subscription, they say as you do.. Start at one turn out and then load 'em up till they level out.

Maybe this IS simple. I hope.

 

[hkeiner]

Re: a few tuning questions

I was told that a lean burn condition would easily smoke a piston, hence the caution with the richness.

I used to worry about this too when I was tinkering with my IDLE jets to find the best setting for smooth idle and good accelleration. It was not until I later learned/understood that the IDLE jet adjustment does NOT risk damage to the pistons even if the IDLE jet is incorrectly set too lean. This is because IDLE jets do not have any meaningfull effect (if at all) on the air/fuel mixture when the motor is running at higher speeds. Only the HIGH SPEED jets affect the air/fuel mixture at higher speeds. This is where piston damage is risked due to a lean air/fuel condition. After I learned this, I could tinker with the IDLE jets without worry, until I found the sweet spot IDLE jet setting.

(This bit of knowledge was very usefull to me as a newbie owner of a used 150 HP V6 carbed motor. It is surprising to me that my shop manual did not explain this. If anyone out there feels that my above understanding is incorrect, however, please let me know and I will remove this post to avoid misleading anyone.)

 

[achris]

Re: a few tuning questions

I used to worry about this too when I was tinkering with my IDLE jets to find the best setting for smooth idle and good accelleration. It was not until I later learned/understood that the IDLE jet adjustment does NOT risk damage to the pistons even if the IDLE jet is incorrectly set too lean. This is because IDLE jets do not have any meaningfull affect (if at all) on the air/fuel mixture when the motor is running at higher speeds. Only the HIGH SPEED jets affect the air/fuel mixture at higher speeds. This is where piston damage is risked due to a lean air/fuel condition. After I learned this, I could tinker with the IDLE jets without worry, until I found the sweet spot IDLE jet setting.

(This bit of knowledge was very usefull to me as a newbie owner of a used 150 HP V6 carbed motor. It is surprising to me that my shop manual did not explain this. If anyone out there feels that my above understanding is incorrect, however, please let me know and I will remove this post to avoid misleading anyone.)

'Ouch' said the nail!

 

[jeff_smith_0423]

Re: a few tuning questions

I thought the lean-burn advice was suspect, but my only previous experience with two strokes is with very small engines, and even idling them lean can cause damage. I really didn't want to blow up this motor since i got a pretty good deal on it and it will probably power my next project boat as well (if it holds up)

 

[hkeiner]

Re: a few tuning questions

I thought the lean-burn advice was suspect.

Just to be clear, the risk of piston damage due to lean-burn at higher speeds is very real. Lean-burn at higher speeds can be caused by a variety of things, such as gummed up carbs, incorrect float adjustment, gummed up high speed fixed jets, weak fuel pump, or restrictions in the fuel line, to name the most common. It is just that lean IDLE jet adjustment is not one of them.

My earlier comments applied to high horsepower 2-stroke carbed Mercury outboard motors that have adustable IDLE jets and fixed HIGH SPEED jets, such as mine. Smaller outboards, lawnmowers, and other 2-stroke motors with different carb and jet setups may have different risks when adjusting jets.

 

[jeff_smith_0423]

Re: a few tuning questions

Yep. i gotcha. fortunately the carbs have been recently cleaned and rebuilt, the fuel pump has been rebuilt, and i have fixed highspeed jets that are clean as a whistle.

I'll attempt to lean it out and try to get it running again for a decent period of time, check the plugs, and hopefully i'm in good shape. If not, i guess i'll be looking for something to life the powerhead with :S

Oh - and just to be clear - i wasn't referring to ANYONE's advice in this thread as suspect...

 

[hkeiner]

Re: a few tuning questions

Oh - and just to be clear - i wasn't referring to ANYONE's advice in this thread as suspect...

I didn't take it that way at all. I just realize that there are lots of different carb designs and sizes of 2-strokes out there and I didn't want my earlier comments to be incorrectly understood as applying to any and all 2-stroke motors, when my comments very well may not be applicable in some cases.

 

[MercFan]

Re: a few tuning questions

I hope I'm not giving advice that's already been covered, but did you check the primer bulb directly after the engine died? I't should be 1/2 to 1 pump from stiff. That's assuming that your initial startup take about 3-4 pumps to stiff.

If it isn't that close to stiff when the engine dies I'd suspect air intrusion on the tank-to-pump line, or some debris in the line or tank.

 

[sailingwest]

Re: a few tuning questions

I too was worried about lean burn on idle mixture ,now i will be happy to tinker away as I always back out a half turn from where I think its right just in case .Thanks for info ,and greetings from Loch Lomond Scotland .Jim B

 

[Chris1956]

Re: a few tuning questions

Jeff, Since that is a freshwater motor, the likelyhood that the exhaust covers rotted out is small. Actually, the exhaust cover bolts could be loose, allowing some cooling water to get into the motor. The inner exhust cover bolts are epoxied in at the factory, so they will not be loose, but the outer cover bolts do get loose. If yours are loose, buy some gaskets and replace the gaskets you have.

BTW - pulling the powerhead on that model is no big deal. Remove electriv quick disconnect and the lower unit first, then the cowling supports and starter and wiring. The powerhead mount nuts are under the trim that says "85HP". Four stainless steel sheet metal screws hold this trim on. The block will be light enough for you to lift.

 

[jeff_smith_0423]

Re: a few tuning questions

quick update. Unless i have a water intrusion isssue on top of what i've found, that's not the case. Thankfullly. Hauled it out of the garage today and attempted to get it running. Same symptoms as when it first conked out. Very hard starting, only keeps running when i give it massive amounts of fuel, and is very boggy.

Once i got it running to the point where i could leave the helm, i hopped off and pulled the #1 wire. No change. Kept running. Pulled the #2 wire. Kept running. Pulled #3, finally got it to die.

SO - i have an ignition problem. Since it's two cylinders i'm temporarily ruling out a compression issue. My gut tells me that it'd be a pretty rare situation to lose compression on two cylinders at the exact same time. I'll check it for certain once i get ahold of a suitable tester. I'm hoping that NAPA can order me the sierra equivalent of the mercury guage. I can't justify spending $42 on a tool that can only check three of the four cylinders.

I did pick up a spark tester. I won't be able to test until i get someone to crank the motor for me.

Suggestions on troubleshooting past that point? The wires look 30 years old, so i can certainly see the need to replace them as part of the process, but i'm not a big fan of throwing parts at a problem beyond that.

I did notice that one of the wires on the switch has lost most of it's insulation and is quite frayed. (rodents?) I'll get a picture up here of that damage. I have no idea what the wire is responsible for, but the motor has ran in this condition. Hopefully i didn't fry the switch box.

 

[jeff_smith_0423]

Re: a few tuning questions

Here's the switch.. The wire i'm talking about comes from the second connection at the bottom and was originally insulated white.

 

[Yepblaze]

Re: a few tuning questions

Excuse me if I missed some pertinent data, but.................

Have you tested the compression?

Just pulling plug wires and condemning the ignition is wrong!

Perhaps you could get the test procedure and equipment to test it.

#1&2 probably share the same carb.

And just from mounds of experience, just because a carb, fuel pump, or what ever has been serviced in the past does not alleviate it from the possible need of attention at any time.

If you suspect 1&2 not pulling their share, pull the plugs and look at them. Are they wet or dry.

Try a squirt of fuel mix in top carb while running, does it light off?


If simple idle mixture screw adjustment does not rectify your situation move on with the diagnostics.

If you believe 1&2 aren't firing move on with diagnostics.

If you suspect the ignition is faulty test the spark with the appropriate tool or procedure. Make a decision and move to the next step.


I probably would have suspected fuel starvation, or flooding. Flooding you will usually see, depending on motor angle, as a leak out of the carb, and wet plugs.

A fuel starvation might be eliminated from concern with a squirt of 50:1 in the suspect carb.


PS In many cases with older Mercury motors, the more you "touch" any wiring the more insulation has a way of falling off, as these old motors used some insulation that has gone beyond it's usable life.

 

[jeff_smith_0423]

Re: a few tuning questions

I certainly will get the compression tester and get it tested. I just can't source the appropriate mercury/sierra tool locally, and it doesn't make a lot of sense to purchase a tool that won't give me an accurate diagnosis (fourth cylinder is almost impossible to get to). The reason i jumped to ignition is the manner in which the problem arose. It was immediate, not under any load, engine wasn't even at full operating temp. It just cut out and died, with the hard restarting and aformentioned "no-fire" symptoms persisting since then.

I've ruled out starvation, as the carb throat is wet with fuel, and i can further bog the motor down by closing off the carb throat with my hand.

It *could* be flooding, but both carbs and the fuel pump were rebuilt a week ago, and the idle mixtures are now set at about 1 and a quarter turns out. If it was true flooding, I think that I would have been able to start it pretty easily once the fuel evap'd (sat with plugs out for two days).

So, i've jumped to ignition since i can troubleshoot that a lot easier right now than compression. This is the first motor i've ever seen that could successfully run on only two of four cylinders. Call me amazed.