My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the rest

[Texasmark]

I spent a few minutes looking for access to the archives and I couldn't find them...help would be appreciated there, but not the issue.

Last time I was out (Mayish timeframe) after a stellar hour or so (off and on) of my usual blasting around the lake at WOT like I like to do, my trusty '02 3 cyl 90 got cranky at the dock when I started it to load it onto the trailer...wouldn't idle long enough to put it in gear and give it some gas.

Last couple of days I started going through it and found a couple of issues: Fuel and spark.

The following happened today in the driveway, 80F on muffs....pee was stellar.

1. Fuel: I found that the plastic linkage that controls the butterfly valves in the carbs is worn to the point that you can't force the valves fully open. In the process of fooling with that, the throttle rod came out of the holder (apparently worn in need of replacement) on the throttle cam and the engine went to some sort of wild rpm's......tach pegged at 7k on muffs no load. Was like that for 2-3 minutes. I tried turning the key off on the remote and it had no effect so I tried to pinch off the fuel line and that didn't work, so I went over to the throttle cam and backed it off manually (not connected to remotes due to malfunction of bushings it seats in) till I manually got the carb butterflies closed and was able to shut her down. The key on a brand new 2000 remote failing (where it worked just fine other than this rpm runaway) is one thing, but not the center of attraction here.

So now, I know a stock Merc 3 cylinder will run over 7grand for over 3 minutes "without puking it's guts" with no load on the engine. So when I get her fixed, the 5600 to 6000 I should be running under load will be a walk in the park.
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2. Ignition: First of all I eliminated fuel as a culprit as I disconnected my fuel line to my built in tank and put it into a container of fresh gas that I bought a couple of days ago.....changing from fuel with Sea Foam that was about 6 mo. old to fresh straight fuel had no impact on the problem. Additionally, I changed my low speed carb. needle positions from the recommended 1 1/4 min setting to a full 2 rev setting to ensure that a lean mixture had nothing to do with the "sneezing" I will talk about below.

Plugs really sooted up today and I put in 2 sets of new plugs with no effect. Lots and lots of exhaust smoke.

First off I had a very hard time controlling rpm's today even with the linkage problem. I fixed the linkage so that it was in a constant position and the engine continuously surged anyway. Like at idle, minimum I could get using the idle set screw on the throttle linkage, was 2k.
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Problem other than that is sneezing on a precise regular basis, about once per second and when it sneezes a blast of exhaust gas blows out the tail pipe. It was obvious that one cylinder was loafing, but finding it was a daunting challenge I haven't as yet mastered. All this happened before and after the 7 grand rpm runaway with no change.

I ran on one cylinder at a time and found the #1 cylinder to do the sneezing and 2 and 3 would labor the engine along as one would expect with 2 of 3 cylinders disconnected. I had the plug wires of the other 2 capped on plugs that I had grounded externally and the non firing plugs were still installed in their sockets with no fire to them....dead cylinders.

I then moved the CDI from #2 to #1 (plug wire and trigger input) and thought I had it nailed to a trigger input problem to #1 but that result is inconclusive.

Sooooooooooo you guys, want something to occupy your time when you feel bored and "nobody loves you (grin)" chew on this if you choose.

I did run the Stator resistance test with the ohmmeter for all 3 CDI's and it was 708 digital ohms exactly for all 3 with a book value of 670 to 710. The input terminal resistance tests for all CDI's were identical.

One CDI is about a year old with PN 827509-A9 whereby the other 2 are original '02 versions at A8's.

Ok guys, do your stuff.

Thanks,

Mark

 

[Faztbullet]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

the engine went to some sort of wild rpm's......tach pegged at 7k on muffs no load.

Called 4 stroking and can scatter a engine in a heartbeat as it breaks the piston shirts, but thing to do is choke the p*** out of it till it dies. Index the flywheel and check TDC on all cylinders as it sound like a switchbox timing problem. Had a 4 cylinder 115 not to long ago doing similar problem

 

[Texasmark]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

Called 4 stroking and can scatter a engine in a heartbeat as it breaks the piston shirts, but thing to do is choke the p*** out of it till it dies. Index the flywheel and check TDC on all cylinders as it sound like a switchbox timing problem. Had a 4 cylinder 115 not to long ago doing similar problem

Ok man, thanks for the quick reply, how about the rest of it....sorry for the length, but everybody (me included) wants more info so I tried to supply what I knew.

Mark

 

[Texasmark]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

Bump

 

[Sprky]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

Called 4 stroking and can scatter a engine in a heartbeat as it breaks the piston shirts, but thing to do is choke the p*** out of it till it dies. Index the flywheel and check TDC on all cylinders as it sound like a switchbox timing problem. Had a 4 cylinder 115 not to long ago doing similar problem

Four stroking

http://www.mopedarmy.com/wiki/Four_Stroking

The condition is called run away. The engine is running on preignition, no spark needed.

Your idle situation sounds like one butterfly is open a little farther than the others. Pull the air box cover and physically look in the throats of the carbs. Insure all the butterflys are closed.

 

[Texasmark]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

As mentioned the last few minutes of my last time out indicated that I had developed an engine problem.

It's been 6 months, like you said we are in a drought here, but yesterday I decided to start looking around at the general condition of the engine and noticed a few things initially:

Top butterfly was not quite lined up with the other two and the throttle cam arm would not advance far enough to open my butterflies completely. Since I'm interested in getting solidly over the 50 mph mark those two things are a big deal to me...but I have a lot more fish to fry before I get back to worrying about that.

So I started investigating and found quite a bit of slop in the mechanisms that connect the remote throttle cable to the carbs and timing (apparently worn plastic bushings that I didn't know were worn...will change). I cleaned up some of that, including balancing the butterflies, and took it outside to test it and there upon discovered my bad running problem that apparently occurred during the last few minutes of my last outing.

I started trouble shooting to isolate the problem and in the process I had several things going like trying to understand why I couldn't get my idle down (throttle linkage set screw) and what/possibly which CDI if that, was causing my sneeze, opening the needle valves another half turn to ensure that it wasn't a lean running sneeze, and removing my fuel line from my BI tank and putting it in a bottle of fresh fuel to ensure that I wasn't fighting a fuel issue.

The runaway caught me completely by surprise as I had never had that happen before. I saw the tach peg 7grand and I guess I had a panic attack. When the ign key wouldn't shut it off I really got worried fast. The rest of the story is in the initial posting.

Thanks for your constructive comments.

Mark

 

[Sprky]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

Off topic.....sorta.


7000 is a walk in the park for cast pistons, so... Why would 7grand w/o the motor being loaded, be any harder on the pistons then 7grand with the motor under a load. Does loading the motor change the wear or stress on pistons as opposed to unloaded?


Not being combative.....

 

[Texasmark]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

Off topic.....sorta.


7000 is a walk in the park for cast pistons, so... Why would 7grand w/o the motor being loaded, be any harder on the pistons then 7grand with the motor under a load. Does loading the motor change the wear or stress on pistons as opposed to unloaded?
Not being combative.....

I would say (conjecture) that loaded vs no load would keep slop in the engine (dimensional clearances between parts being necessary or from wear) running smoother. Comment comes from many years of carbureted engines, being 4 cycle auto or small engines that you couldn't get the engine to idle smoothly unless it was "in gear".

Relating to 2 strokes and the lack of all those parts to wobble around probably not. Probably as you said, not a problem and you would get more piston skirt scuffing with the engine under load.

Other than screaming, the engine ran like a top and after I got her quieted down and restarted, it ran like it did before......which brings up a point I was thinking about last night: If the engine is capable of running 7+ how is it that it acts so sorry at idle and low rpm's? Well, in re-reading this post just now before submitting it, I just realized that pre-ignition doesn't need the stator, trigger coils, trigger ckt, CDM or spark plug. Ha that makes it simple.

I think I have one answer to that and it leads to the CDM. If the storage capacitor in the module is defective, it may not be capable of staying charged up during the long inter trigger intervals that occur at low rpm whereby at 7+ or even 3-4k it runs perfectly.

idle is roughly 1000 rpm (on muffs) so the charge/storage interval would be 1000/60sec = 16 rps and the time per cycle would be 1/16 = 62.5 milliseconds......a long time for a high sped capacitor (0.1 or 0.01 microfarad) to hold a charge especially if it had a bleed resistor across it. Whereas at 5k the time would be 1/5 or 12 ms.......quite a change.

---------------- Brief interruption. Yesterday when I had the runaway, I had he linkage disconnected and was moving things around with the throttle linkages trying to see what made a difference and what didn't and I think while the engine was running I advanced the timing long enough to get the pre-ignition started. Never occurred to me at the time that I could do that and the engine has never done it before.
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Back to the story: Today I will get back to investigating and will first ensure that I hook the throttle linkage back together. I pretty well think the CDM (827509-A9) that I bought a few years ago is good. Today I will go back and run on a single cylinder at a time with this CDM and verify that it will run all cylinders without sneezing. Once I confirm that I will do the same with the other 2 and see what happens. As stated pretty sure 1 is bad and maybe both the old ones. I know to have all them plugged in so that the charging circuit has a complete path and I will deadman the plug wires to plugs not installed in the engine but grounded cases....will leave all (other) plugs in engine during testing.

After that, I'll get the manual out and go over the trigger and Stator voltages per the manual.

After a bumpy start, we might enjoy each others "company" after all. Glad things are going as they are.

Mark

 

[Sprky]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

After a bumpy start, we might enjoy each others "company" after all. Glad things are going as they are.Mark

Poof.................

 

[Texasmark]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

Well Sparky, you have some interesting information. I read it and may digest it over the next few days as we are scheduled for showers this PM and tomorrow....yeah right.

Right now I am still up in the air on the solution to the problem, but the problem is obviously a loafing cylinder and at a rythmetic,roughly one cycle per second or two rate, the missing cylinder catches for a rev or two, belches a load of smoke out the tail pipe and shuts back off.

I spent most of the day taking data with a lot of it a waste of time....substituting what I thought to be a good CDM in the other two slots and evaluated the results. Made about 7 test runs and have the data from them and nothing conclusive.

Aside from that, I did the following:

Compression test at cranking speed was 117 psig within 2 psig between cylinders. I checked the accuracy of the pressure gauge taking the measurement and it was so close to to another gauge that I blew it off as being accurate. My Merc manual says that 120 is good and below might cause some problems......well I'm not that far from 120. So that's out.

I built a DVA and used a sharpened wire to sample the signal/voltage into my CDM's (trigger and stator since I didn't have the test wiring harness....didn't need it) and they were all within spec. Won't bore you but they had some variance but were well above the mins and below the max's.

I spent several hours substituting the CDM's on different cylinders and different CDM's on different cylinders......after all that and I have the data, I have no conclusive evidence that a CDM is at fault.

The lingering problem is that it is obvious that one cylinder is loafing (engine missing while not coughing at idle/low rpm) and I have this repetitive, cyclic, sneezing at the rate of about once per second or two at idle speed which is uncontrollable on muffs within the 1-2k rpm range.

I can't go chasing a carb problem with something like that. Not that it's not the problem, but I am a mechanism guy and the mechanism for a carb problem just isn't there. To me a carb problem would be constant or variable in it's influence and changing the idle jet setting would influence it which it doesn't. A carb isn't going to allow you to run for 20 seconds and then rythmetically sneeze and repeat the process. Besides, if I had a carb problem, how could I run 7+g rpm on pre-ignition.

We, and all following are going to grow from this. I will get to the solution and share the path with the forum but it may be after 1st of the year. We, as you said are in a drought and I really have no incentive to fix this today.

Mark

 

[Sprky]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

Suit yourself

 

[CharlieB]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

Carbs out of 'sync' can cause a 'leading' cyl, that is the carb that is passing more air is trying to accelerate the motor, which is also causing that cyl to run substantually hotter than the others.

If there are carbon deposits on the piston dome and cyl, they can become hot enough to 'glow' and cause pre-ignition, which can also cause a flashback thru the transfer ports and crankcase, acting asmost as a lean cough or sneeze.

Do a de-carb, link and synch, and see if the condition clears.

 

[Texasmark]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

Carbs out of 'sync' can cause a 'leading' cyl, that is the carb that is passing more air is trying to accelerate the motor, which is also causing that cyl to run substantually hotter than the others.

If there are carbon deposits on the piston dome and cyl, they can become hot enough to 'glow' and cause pre-ignition, which can also cause a flashback thru the transfer ports and crankcase, acting asmost as a lean cough or sneeze.

Do a de-carb, link and synch, and see if the condition clears.

Charlie,

This problem apparently started after an hour or two of rather hot weather running at WOT off and on, some midrange cruising. Everything was stellar. Engine ran perfectly and had no problem with acceleration nor getting my usual WOT rpm's. Actually I had a 200# passenger (normally boat alone) and had just ported my prop and I was getting 5800 rpms rather than the 5600 I had run before the porting.

I pulled into the no wake zone and it took several minutes to idle to the dock....no problem. Shut her off, got the trailer, and upon attempting to restart it didn't want to idle long enough for me to get it in gear and advance the throttle. Something obviously crashed.

On what I have done the last couple of days, aligning the butterflies (one was a few degrees off) and resetting the carb jets, taking the slop out of the linkage, and chasing the missing cylinder/repetitive boom (not really a sneeze, an instantaneous blast of rpm and pile of smoke out the exhaust. All that is documented above.

The crown of the pistons are almost immaculate. They are very close to being smooth. I keep well over the recommended dose of Sea Foam in the fuel. If I don't use the boat for a very long time, I drain the fuel and start the next trip with new fuel. I use Quicksilver premium oil. The engine is big and the boat is light. Most of my running is in the top end of the power band and 5600-5800 is my WOT redline which obviously indicates that I am not lugging the engine. Plane out takes about 2-3 seconds.

I was amazed at my runaway I described a day or so ago. One would think that to "glow" and cause a preignition runaway, you need something to glow. Nothing there. But it did.

After all the checks yesterday I can only surmise that I have at least 2 malfunctioning CDM's. I am pretty sure the new one I bought a few years ago is ok....it's an A9 mod where the orig ones are A8 mod. With current models being A10 it sorta tells me that Merc has had problems with these things over the years.

Sorta off topic, I changed the fuel filter since I had one handy and just decided to do it, and upon removing the original (2002 engine), I could blow through it as easily as the new one attesting to the fact that I use good fresh, clean fuel.

Again, your help would be appreciated.

Thanks,

Mark

 

[Texasmark]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

Suit yourself

I'm still open for suggestions. Right now I/we seem to have turned over all the rocks and until I buy (3) new CDM's don't know what else needs to be done.

If you want to chat more come on.

Thanks,

Mark

 

[Sprky]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

I'm still open for suggestions. Right now I/we seem to have turned over all the rocks and until I buy (3) new CDM's don't know what else needs to be done.

If you want to chat more come on.

Thanks,

Mark

Naa........I'm looking forward to calling you a dumb azz when you install the cdm's and the motor does the same thing.

I have used cdm's I will sell cheap!

 

[Texasmark]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

Naa........I'm looking forward to calling you a dumb azz when you install the cdm's and the motor does the same thing.

I have used cdm's I will sell cheap!

Ha Ha. No way Jose! No way I'll buy one of those used, especially if it's not an A10 derivative, and even if it is, no way.

I don't have any of those fancy gadgets on this engine that a lot have...separate switch box, over rev limiter, pressure pump monitor of some sort, blah, blah.

All I have is a Stator and a Trigger and 3 CDM's. Since both S and T are magnetic, if they were bad, they would stay bad, maybe under certain circumstances, Heat/cold primarily, but would stay in that condition for the duration of whatever caused the malfunction. On the other hand, lots of funnys can happen with the CDM. I made a comfortable living off CDM's on a grand scale (same principle, different application) and associated circuits for 36 years. I know a tad about their peculiarities.

So, that's where I am and when I decide to buy them and some replacement linkage plastic "stuff", I'll post back on how things are doing.

Mark

 

[CharlieB]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

Charlie,

This problem apparently started after an hour or two of rather hot weather running at WOT off and on, some midrange cruising. Everything was stellar. Engine ran perfectly and had no problem with acceleration nor getting my usual WOT rpm's. Actually I had a 200# passenger (normally boat alone) and had just ported my prop and I was getting 5800 rpms rather than the 5600 I had run before the porting.

I pulled into the no wake zone and it took several minutes to idle to the dock....no problem. Shut her off, got the trailer, and upon attempting to restart it didn't want to idle long enough for me to get it in gear and advance the throttle.

WITH an additional 200# load it ran 200 RPM above the norm?

PORTING?

What changes had you made before this run?

Porting? Any jetting changes? Float heights?

Have you done a high speed cut off and read the plugs?

 

[Sprky]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

I figured you either had a "Double E" or worked with a bunch of Double E propellerheads.

Your still running in the wrong direction!

 

[Laddies]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

Have you checked to see if a sleeve is moving, thats a common problem with the 3 cyl engines

 

[cr2k]

Re: My turn. Hello Certified Merc engine mechanics, Faztbullet, CharlieB and the res

running a overdose of seafoam or even oil is running the engine lean. the jets are only so big and set to allow so much fuel through, fixed setting. By adding other additives you are diluting the fuel that gets to the engine. i.e. at 50 to 1 you get 50 parts of fuel to 1 part of oil, now add seafoam you will get 1 part oil say 2 parts seafoam and only 48 parts of fuel.

I would also check the exhaust cover to make sure the gasket hasn't blown some where.