Bad thermostat? Motor RPM Surging

[gwoloshyn]

I have a 1989 Evinrude 110hp (not sure of model year) that isn't running properly. It starts right up, but throughout all RPM ranges, from idle and up, the RPM surges plus or minus 1k. The carburetors are clean, powerpack brand new (just put this on to find out it did not solve my problem), and all coils throw spark.

I've narrowed it down to a possible bad thermostat. Do my symptoms match up with a bad thermostat? The motor does run very warm, nearly hot to the touch at idle (and only after idling for a SHORT time). This is a brand new re-manufactured motor from Outboard Exchange. I wouldn't recommend them AT ALL, this, among other issues i've had with them.

Can anyone help me with a possible diagnosis?

 

[gwoloshyn]

Re: Bad thermostat? Motor RPM Surging

Anyone have an idea? I cannot figure out the problem..

 

[sutor623]

Re: Bad thermostat? Motor RPM Surging

Well this being a carbureted motor, Im not sure what else would cause a surge in idle. Sometimes when these motors overheat they will cut back to 50% RPM. If you suspect the thermostat you could always pull it and see how she runs with no thermostat. If it changes the issue then just get a new thermo. If that motor is running hot you could be having much bigger issues here soon if you dont really get to the bottom of this. Has the waterpump been changed recently?

 

[sutor623]

Re: Bad thermostat? Motor RPM Surging

And if you need a temporary thermostat gasket, you can use the silver stuff they sell at autozone. I have used these to seal my waterjacket in many motors, and no issues at all.

 

[emdsapmgr]

Re: Bad thermostat? Motor RPM Surging

Probably want to rectify the temp problem first. You've not mentioned any actual cyl head temps, nor did you mention hearing the overheat warning horn. It may be just fine. You should rent or borrow a laser temp gun. Check the head temps when the engine is fully warmed up. At idle, it should be between 143 and 153. That's normal. Anything higher and it's a problem. Your surging could be a spark issue. When the engine is starting to act up, remove the cowling, then put an inductive timing light lead on each of the 4 plugwires. The flashes from the gun will show the quality of spark on each. Compare the flashes: look for intermittents, no fires, weak firing.

 

[metriccrescentwrench]

Re: Bad thermostat? Motor RPM Surging

When the engine is up to operating temperature (the spec on mine is 140 deg F at idle, dropping down to 125 deg F at speed) it's going to feel hot to the touch. At 140-ish you can only hold your hand on it for 5 or 10 seconds before it becomes painful. So, it doesn't sound like it's hot, but you should definitely verify that. Also, on the engines with SLOW mode they'll limit the rpm to 2500 and will stay in slow mode until the ignition is turned off, not jump in and out of SLOW mode.

Just for the sake of being thorough you probably ought to check compression.

You said "all coils throw spark". What did you test spark with? The standard method is to use a variable gap spark tester set at 7/16".

In my limited experience I'd be more inclined to suspect a fuel problem, or else something like a leaking gasket. (But definitely also check for intermittent spark).

 

[kenmyfam]

Re: Bad thermostat? Motor RPM Surging

Agree. take care of the cooling problem first.
How is the fuel delivery to the carbs ??

 

[gwoloshyn]

Re: Bad thermostat? Motor RPM Surging

I will verify the temp but after doing more research I think I probably have an air leak somewhere in my fuel system. I saw some bubbles in my fuel filter when priming it, so I am going to hook up a portable tank and see what I get.

Engine surges is consistant with an air leak

 

[gwoloshyn]

Re: Bad thermostat? Motor RPM Surging

I am at a COMPLETE loss for what to do next to figure out this problem. After doing alot of reading I thought for sure I would have an air leak/fuel delivery issue, which I still think I do, but I can't figure out what is wrong! Here is what I have done with no fix to the problem:

Carbs completely clean
New fuel pump
New fuel lines with clamps
Tried 2 new primer bulbs
Tried hooking up a brand new portable tank (no difference)
Brand new powerpack
Spark plugs jump a 7/16" gap

The engine is idling and surging through RPMS, a few hundred at a time, and will not run steady. The motor also gets fairly warm very fast, but I haven't verified the actual temperature yet.

I am completely out of options to try, and REALLY don't want to tow my boat a few states away to CT where I bought this POS.

 

[gwoloshyn]

Re: Bad thermostat? Motor RPM Surging

I am at a COMPLETE loss for what to do next to figure out this problem. After doing alot of reading I thought for sure I would have an air leak/fuel delivery issue, which I still think I do, but I can't figure out what is wrong! Here is what I have done with no fix to the problem:

Carbs completely clean
New fuel pump
New fuel lines with clamps
Tried 2 new primer bulbs
Tried hooking up a brand new portable tank (no difference)
Brand new powerpack
Spark plugs jump a 7/16" gap

The engine is idling and surging through RPMS, a few hundred at a time, and will not run steady. The motor also gets fairly warm very fast, but I haven't verified the actual temperature yet.

I am completely out of options to try, and REALLY don't want to tow my boat a few states away to CT where I bought this POS.

 

[1NewBoatGuy]

Re: Bad thermostat? Motor RPM Surging

OK, going through these same types of problems my self with my motor. I can give you a few ideas.
Check spark with a timing light. using a plug tester or something else may not tell you how well your plug wires are connecting. I found this out today.
My motor was running rough and getting frustrated I dropped it off at the marina to have it checked. The guy found the spark plug wires are not making a good contact with the plugs. I verified this my self with an inductive timing light at each wire. There were very intermittent. This is what I would check first if I was you. I checked mine with a spark plug tester and because the connections were tighter using this it didn't show a problem, again using the timing light I got no flashing light on two of the cylinders. This verified my problem instantly.
Again, what you need for an engine to work is fuel, compression, spark, exhaust. Fuel delivery is a easy problem to troubleshoot. Rebuilding carbs is normally not so necessary if you have been keeping up on maintenance when storing your boat. There really is not much to them.
Gaskets are the major culprit with carburetor or fuel mixture problems, especially on older motors.
I hope this helps, I am pretty new to boat motors, but have been working with small engines, cars, trucks and tanks for years. So I am not a noob to mechanics anyway.
Plus over the past few months I have had run the gambit with boats and motors through trial and error I am learning a lot...

 

[Will Bark]

Re: Bad thermostat? Motor RPM Surging

May have missed it; but does your clean carbs include spraying carb cleaner thru all orifices and then running a wire from bread wrapper tie thru them and then blowing all out with compressed air? Sounds like carb still has varnish in it or the carb has gone south on you.

 

[1NewBoatGuy]

Re: Bad thermostat? Motor RPM Surging

If you have an intermittent connection on a spark plug, what happens is when it does throw a spark the engine will surge due to the increased fuel in the cylinder and additional spark. You may also get a backfire every so often. If all plugs are firing consistently as they are intended your idle speed will slow down, be more consistent and your motor should run smooth.

 

[gwoloshyn]

Re: Bad thermostat? Motor RPM Surging

I'll check again with a timing light, but I already replaced 2 of the plug wires. I paid over $5, 000 for this motor and they couldnt even put on new plug wires when they built It.

My heads are getting hot very fast which leads me to believe its a fuel issue or air leak. Make sense? Maybe crank seals? I don't trust this motor or the people to built it, ive been trying to get it going good for the past 6 months since I bought it. All components are new, I would hope.

 

[gwoloshyn]

Re: Bad thermostat? Motor RPM Surging

Here is something I should also add. I have one of those inline canister type filters installed before the fuel pump and when its running it will run real low on fuel and not stay at a constant level. Possible air leak in this? I already tried a new primer bulb and fuel tank.

 

[sutor623]

Re: Bad thermostat? Motor RPM Surging

Vacuum and fuel lines can do funny things. When I had vacuum/fuel pump issues on my '84 rude it just idled poorly, and did NOT surge in RPMs. Honestly I am pointing more towards a timer base and/or stator. Go to the CDI troubleshooting guide and look up your motor. You can either buy a DVA meter or make one via instructions you can find on this site. When electronics fail they are typically intermittent. I had a bad stator and trigger on one of my most recent projects and that motor had sporadic idle and would NOT get on plane. Just because each cylinder is throwing a spark does not mean that it is timed properly, or sending enough juice. Any way you could get us a video of her running?

 

[sutor623]

Re: Bad thermostat? Motor RPM Surging

Try this buddy. This is the way to go. I believe page 39-57 explains your engine. ISSUU - CDI Electronics Troublbshooting Guide - 2012 by CDI Electronics

 

[itsaboattime]

Re: Bad thermostat? Motor RPM Surging

I have an '87 vintage of the same motor. They heat up rather quickly. Your starboard(right) bank of cylinders will be hotter than your port(left) bank. Mine runs about 138-140, port and 143, starboard. Checked with an IR thermometer.
What do your plugs look like? Do they all look the same?

 

[emdsapmgr]

Re: Bad thermostat? Motor RPM Surging

That engine was not shipped from the factory with an inline canister filter. Always possible that a weak fuel pump might not be able to suck fuel through that filter. Might want to eliminate that variable from your system till you get it going correctly.

 

[gwoloshyn]

Re: Bad thermostat? Motor RPM Surging

Thanks for all the replies. I actually did just that, I removed the canister filter from the system and fed my fuel line directly into the pump and took it out on the lake for a test run. It ran great!

My cylinder head temperatures are running from 120-130 at all times.

Now, this engine has brand new pistons and rings, I'm in the process of breaking in the new engine. That being said, after I got home I pulled the plugs and each did look slightly different, varying from all black to a light brown. Are different spark plug colors normal for a new engine?