Cannot Idle under 1500 - 1800 RPMs

Hi, Can really, Really use some help on this one. I'm a overall decent mechanic but this has me stumped. Hopefully someone can assist me?? Any Suggestions are most appreciated.

Background; I have a dock space so the Pontoon boats is in the water all year. Was Running like a top for the last couple years and started and ran Great this Spring. Due to the weather IT was not used /Started for a week. It Was running great - now starts runs rough and very high Idle - 1500 to 1800 RPMS. Will Run in a test drive but very rough and will not reach 5000 RPM (Was 5500 WOT)

1996 Merc 60 HP 3 Cyl Looks to have moderate usage. Bought a couple years ago.


I've done/checked/eliminated the following (not in this exact order);


- No water in Fuel 1/4 Tank. No recent fuel before issue. Had Run over 1/2 Tank of same fuel with no issues Checked for water in fuel with Test paste on test stick. Added Dry gas and 10 Gal fresh fuel from a fairly new and different Gas Station. Changed Engine Fuel Filter. Primer bulb is firm. I Don't believe this is fuel related.

- Then checked Idle setting, Removed Throttle linkage, ALL Throttle plates CLOSED. Linkage and and adjustments will NOT let it Idle down. Moving of Trigger plate will NOT change/ Lower Idle RPM (see below). I see nothing wrong with the linkage, etc. I believe this is OK as well.

- Pulled plugs - Looked OK. Maybe not completely dry. Changed Plugs, Checked Compression All cylinders within 1 PSI and over 96 PSI (Gauge was ancient - but repeatable). All this looked OK was well. Can pull each plug wire one at a time and engine still runs albeit not much change in rough running.

- Thought it may be the Switch box - Changed with MERC New OEM - no change.

- Put on a timing light - at Idle it's at 6 deg ATDC. If I move the Trigger plate - IT does change Timing. It does NOT change the RPMS. IF I idle up to high idle (allowing me to move the trigger plate more) Timing changes to TDC and I can retard to 10Deg ATDC and still NO RPM /CHANGE. Trigger checked with Ohm Meter - tests right in Spec. So Trigger and Timing advance seem to be working OK. I was not so concerned with the timing settings - just the fact that the timing does change with movement of the trigger plate.

- OK Vacuum leak was early suspected as well. Visual looked OK. Nuts tight on Carbs and Reed plates. Pinched off all vacuum lines at Each ends and center of hose. No change. Still always at High Idle. Sprayed with Starting fluid on all hoses, around carbs and gaskets and best possible under flywheel (to check shaft seal). At one point I did get a reduction in RPM but I was spraying so much at the sides on the Carbs - I believe it was getting sucked in the carbs. SO I repeated this with WD40 and it did not repeat. If there is a vacuum leak it's not apparent, fairly large, and occurred very quickly.

So where I am Now? Still same issue. Lots of stuff checked. I see two possible issues to follow up.

- I have read that the Voltage rectifier - if it starts going bad - can cause problems with the Switchbox and ignition. Rectifier was changed (oem) about 2 years ago (to fix charging and Tach issues) but otherwise seems OK. I can try changing this as a long shot. I have a CDI on order.

- Back to basics - It still acting like a Vacuum leak. I'm leaning towards the the top crankshaft seal going bad. I have a seal on order along with the crankshaft puller. Can this seal be changed by pull out push in once it is accessible?? (I;m assuming looking at the Seal and PArts diagrams that you do ?NOT have to split the case to change the seal?)

Well - A lot checked. IT's still idling rough and way to high and cannot lower RPM via adjustments or timing changes.

Any suggestion PLEASE ???

Thanks for reading - SteveC

Might be a bad reed valve. You'll have to pull the carbs off and the plate behind them to see.

I had one like yours that did that. It had a bad reed valve.

Jeff

Update - I changed the Rectifier - no change. Checked fuel tank (clean), changed tank/primer/hose to engine - not that I thought this was the issue - but a little PM for an old hose.

I've tried to find any vacuum leak with starting spray, WD40, and propane form my soldering tank. No change/luck. I would think that a Vacuum leak would affect the running less at higher RPM. Since it's running poorly at 4K+ RPM I think it's not crank seal.

I held a small delicate leaf in front of each Carburetor Intake while running. All pulling into engine - none pushing the leaf away (as a crude check on the reed valves). I'n ruling out the Reed valves - but I'll focus on the fuel delivery for now.

Well, It still runs rough and will not idle down (1200 to 2000 RPM). I Still think it's a lean fuel problem - and since it running rough at high RPM I'm thinking it's the Carbs (Blocked Jet(s) ?, Sticking Float, etc. ).


I've run a half tank of fuel with Gumout and it's still same old.

Next Plans - Re pull plugs to see If I can Id the which Carb.
Pull off Carb fuel line - - drain carbs, fill with Gumout. Pull out low speed jets and blow out with Carb cleaner and replace. Let it sit overnight.

If this fails - I'll pull and clean the 3 the carbs and "hopefully" be able to see if a reed valve is open or missing.

In the meantime - It's in the water and I'll tinker and advise.

Did you try running her on two cylinders, leaving one plug wire off at a time to see how the cylinders balance?

Jeff

Hi Jeff - thanks for adding your thoughts. Yes I did. Pulling each Wire one at a time made little difference in the way the engine idled. Which I thought strange but it was a if I did not pull the wire.

Holy cow! Don't know what to say. Have you done a compression test? Auto Zone will lend you a tester if you can't borrow one.

Jeff

I have an old and crappy one. I may not trust the gauge - but I trust it's repeat ability. Pressure for all cylinders were 95 or 96 PSI with Throttle plate tied fully open. This WAS running just fine - it sat for a week due to crappy weather and then started right up running too high on idle and a little rough. Runs off idle rough and crappy and gets to 4K + only, but it does run.

just curious.......when you are done for the day, do you disconnect the fuel line and run the carbs dry, or do you just shut the engine off and walk away ? i am not being cynical.

crankbait said:

just curious.......when you are done for the day, do you disconnect the fuel line and run the carbs dry, or do you just shut the engine off and walk away ? i am not being cynical.

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No problem with the question .... First I did just re drain the carbs (kept on motor), blow out / blow in carb spray into the vent, Low speed jet, brass tube (in entrance to carb throat) an then fill with gum out. Sat 24 hrs then drained and re started 2nd try. Still runs high Idle and a little rough. Also Changed the Tank /primer bulb to engine line - looked ok but was 17 years old. Just in case. No difference.

Your Question - and thanks for the reply - I live on a small lake in New England and have had multiple outboards and an I/O over the years. I do most all repair and maint. I also worked for years at Sears fixing small engines and 2 cycle outboards and chainsaws.

In Short ( I Know too late!), I leave the boats in the water all year with gas in the carbs. Shut it off and walk away. Normally motors are re started every week. Been doing this since the 70's. Never had to clean a carb/had a problem like this. Also - the fuel that was in the tanks at the start of this did have MErc Quick kleen added to the fuel. In my experience, there are two trains of thought on storage of motors - one is drain the gas, the other is use a fuel additive/stabilizer and leave the gas in the carbs and fuel in the tank. Both have up and down sides. I normally use the latter. I'd rather keep the seals wet not allow to dry and gum up. My choice but either work.

Not many seals in a carb to 'dry out', but ethanol gas left in them will create all kinds of hell! The prevailing opinion is to run 'em dry every time.

Jeff

I have re-read your posts a couple times. Are you saying that will not idle under 1500/1800 rpm with the throttle plates closed; or are you say that to keep it running you need to set the throttle lever such that it will only run at a minimum rpm of 1500/1800. One problem is completely different than the other.

If it were my motor, I would go back to the carbs. Carbs are some the most mis-understood part of an internal combustion engine. They have two or three fluid flow circuits selected by throttle plate position and venturi effect differential pressure. The fact that your spark is good on all cylinders at low RPM and that it is hard starting, your carbs are not clean. Snake Oil (ie.. gas additive fuel system cleaner) is not a solution for an already gummed up carb, it may help it stay clean but will not undo already in place damage.

ALL the reputable marine mechanics in my area ultrasonically clean carbs and probe/clean very small port with a fine brass wires. It is not a quick process. I follow their lead at home with a 6 liter ultrasonic cleaner.

These are the carbs off my '86 Merc 60hp. They look like new inside and out.


Take it for what you think it is worth.

FishinLite said:

I have re-read your posts a couple times. Are you saying that will not idle under 1500/1800 rpm with the throttle plates closed; or are you say that to keep it running you need to set the throttle lever such that it will only run at a minimum rpm of 1500/1800. One problem is completely different than the other.

If it were my motor, I would go back to the carbs. Carbs are some the most mis-understood part of an internal combustion engine. They have two or three fluid flow circuits selected by throttle plate position and venturi effect differential pressure. The fact that your spark is good on all cylinders at low RPM and that it is hard starting, your carbs are not clean. Snake Oil (ie.. gas additive fuel system cleaner) is not a solution for an already gummed up carb, it may help it stay clean but will not undo already in place damage.

ALL the reputable marine mechanics in my area ultrasonically clean carbs and probe/clean very small port with a fine brass wires. It is not a quick process. I follow their lead at home with a 6 liter ultrasonic cleaner.

These are the carbs off my '86 Merc 60hp. They look like new inside and out.
View attachment 15765

Take it for what you think it is worth.

Click to expand...

Thanks for the reply! My Motor will not idle under 1500/1800 rpm with the throttle plates closed. I cannot get the RPMs below 1500/1800 RPMs. IT idles a little rough and "might" have a skip. IT also runs rough at higher speeds underway and will not get to full RPM - again may have a skip. I'm wondering if the skip/misfire is causing the higher RPM (i.e. firing before full charge effectively producing a lower energy spark at an advanced timing.)

It was running Perfect until it sat for about 6 days and this happened. I'm going to change the Coils and plug wires later Today and do some more Ohm measurements on the Trigger and Stator. If this fails - it's time to pull and clean the carbs + check the reed valves.

I can not remember who the poster was, do you have a DVA. The jist of the comment was that the voltage from the trigger was actually to high (if I remember correctly just over 10 volts). This to high voltage was causing the CDI to fire pre-maturely. Causing an out of time situation. Replacing the trigger solved the problem. I am pulling this from memory, but all the ohm measurement were in spec.

Good Luck

FishinLite - now that's very helpful info ! My trigger does test OK (Ohms) but I'm still suspect it on this issue. I'm next replacing the Coils and Wire and if that doe not cure the problem I'll pull the boat from the water and pull the carbs to clean, the reed plate to check and the flywheel to change top crank seal. Prior to disassembly I'll do the DVA testing .... I WILL advise on solution - eventually ....

Believe it or not, I'm having the exact same problem my older model triple. So far I tried another stator, ignition coil and trigger coil to no avail. Next comes the switch box (got one on order). I'll let you know anything I find out.

Have you done a compression test on it with a GOOD gage? Those readings of yours--assuming they're accurate--are scary low.

Jeff

fastjeff said:

Believe it or not, I'm having the exact same problem my older model triple. So far I tried another stator, ignition coil and trigger coil to no avail. Next comes the switch box (got one on order). I'll let you know anything I find out.

Have you done a compression test on it with a GOOD gage? Those readings of yours--assuming they're accurate--are scary low.

Jeff

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Hi Jeff. Sorry to hear you have the same issue. When I did the compression test I used a very old gauge and on a cold engine. As the Boat was working perfectly on the previous usage - I was not to concerned. I did want to see what differences I got between the cylinders - which was almost none. However I did buy a new gauge and will repeat the test shortly. I'll advise.

Did you run it at night to check for arcing ?? That's my next check after it stops raining. message me if I can help.

The way my engine is set up. arcing probably isn't an issue. Good idea, though.

Jeff

PS: Above 2,000 rpm mine runs perfectly. Weird, eh?

SOLVED/ FIXED ! Ii was the Stator or the Trigger.

Although I did Ohm test the Trigger Early on, (which tested OK) I finally decided to pull the Flywheel. I changed the Both the Trigger and the Stator.. The top crank seal looked fine and no sign of fuel/air/exhaust leakage - but while I was there I changed it as well. Reset idle timing. Did some final link and sync/idle/low speed jet tweaking - runs like new! I will re ohm check the Stator and Trigger on the bench and IF I fined any bad readings to indicate which item actually was bad - I'll add another post.

Quick history summary for anyone searching for this issue;

Mercury 1996 60 HP ELPTO Engine. Was running just fine/OK . Left to sit in water for almost a week. Cranking was harder and labored. Did start and idle but missing and very rough. Could NOT adjust idle to go under 1500 RPMs. Ran overall VERY rough at any speed.. Would not exceed 4K RPM. Throttle response was much different that normal - (not very responsive to throttle changes) .

Issue found - Although trigger ohmed out OK it was changed (with a new OEM) along with a new Stator (CDI). Not sure which was the problem . Issue fixed.

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Sure wish you could clarify which was the culprit.

Jeff

fastjeff said:

Sure wish you could clarify which was the culprit.

Jeff

Click to expand...

Hi Jeff, I will ohm out the suspect trigger and stator . But give me a few days as I have a lot on my plate right now. My testing may not prove the issue anyway.

IF I was in your shoes I'd do the following .... Ohm out the trigger - and see if it at least test good. IF it's charging OK take a good look under the flywheel and look for any heat /melting on the stator for a hint - just in case. Using the ~$28 Merc puller Pull the flywheel - it was not a problem to pull - at least to me .... I'd buy a trigger ~ $98 on Amazon - and swap it out. You have a 50/50 chance of being right and it should not take more than an hour or two. Half the time was spent routing and connecting the wiring (hint - use a sting to attached to the old cable end, loosen the starter and the electrical box and use the string to pull the new wire harness back through.. The Stator I bought was about $187 Just my opinion.

Done all that and more. So far everything checks out: resistance, general condition of coils and wiring, and even the DVA meter output.

Still guessing...

Jeff