engine running cool.....poor idle....great wot

[roonie]

1977..70hp evenrude. model #70773/70779 this engine has been giving me grief since i bought it used. Works great at full speed and almost everywhere in between but fails to stay idling or trolling speed. I coughs and spits and dies while at low idle either in nuetral or moving.
I read on here about the 3 second test where you put your hand on top the engine to test how hot she runs. Well.....i could keep my hand on the top of this engine for the rest of the day if I had to.
Ive pulled the thermostat this morning and it was closed. Tested the thermostat in boiling water and it seems to be opening properly.
So i guess my question is ...what else could cause the engine to run cool? Would too cold a plug make the engine run this cool?
I read somewhere on here about certain years of these engines giving certain idle issues etc. but cannot seem to find the thread again. I was told that these older evenrudes need to have the low idle speed jet drilled and rejetted.Does anyone have any info that they can post for me. Any help would be great so that i can get on the water.

 

[Monte1961]

Re: engine running cool.....poor idle....great wot

1977..70hp evenrude. model #70773/70779 this engine has been giving me grief since i bought it used. Works great at full speed and almost everywhere in between but fails to stay idling or trolling speed. I coughs and spits and dies while at low idle either in nuetral or moving.
I read on here about the 3 second test where you put your hand on top the engine to test how hot she runs. Well.....i could keep my hand on the top of this engine for the rest of the day if I had to.
Ive pulled the thermostat this morning and it was closed. Tested the thermostat in boiling water and it seems to be opening properly.
So i guess my question is ...what else could cause the engine to run cool? Would too cold a plug make the engine run this cool?
I read somewhere on here about certain years of these engines giving certain idle issues etc. but cannot seem to find the thread again. I was told that these older evenrudes need to have the low idle speed jet drilled and rejetted.Does anyone have any info that they can post for me. Any help would be great so that i can get on the water.

What you are describing is what is known as a lean sneeze at or almost idle. If none adjustable low speed jet, a carb/s overhaul will be needed, provided you have good compression and spark.

 

[roonie]

Re: engine running cool.....poor idle....great wot

The fellow i purchased the boat off of tells me the carbs were done a yr. ago. But ive talked with a boat mechanic and he tells me if they were redone, the gaskets should be brown color, not black......my gaskets are black......any truth to this? this boat at WOT goes 37mph so i doubt it has a compression issue.

I put seafoam into the cyl. yesterday and also into a gal. of fuel as per instructions on this site....never changed a thing. What would a carb job have to do with the engine running so cool?

 

[yoster]

Re: engine running cool.....poor idle....great wot

Roonie, the "hand test" is only to be used to determine if you're overheating. If you can keep your hand on it longer than that, then fine (the test is not designed for testing an engine that's running too cool, only too hot).

Concerning the idling, does it get any better after you've ran the engine for awhile at higher speeds? Many outboards are cold-blooded by nature; take a lot priming/choking at times to get them going at first. I'd also verify that you're running the OEM recommended plugs. Note - the plugs won't really change the engine operating temperature, but can affect idle performance if they're not of correct spec.

 

[Daviet]

Re: engine running cool.....poor idle....great wot

If I remember correctly all of the carb bowl gaskets I have installed for quite awhile were a tan color. But am not sure about aftermarket kits. The carbs have nothing to do with the engine running cool, but they could be causing your low speed problems. Your carbs have fixed orifices and there are no carb adjustments, but the orifices have to be clean with no restrictions to operate properly. Make sure the compression is up to spec, low compression on one cylinder can cause an idle problem, but run ok at high speed because of the other cylinders. Make sure you have the proper spark plugs installed and they are in good shape.

 

[roonie]

Re: engine running cool.....poor idle....great wot

the plugs in this boat are gapped incorrectly, i just found out. They are NGK BZ7HS10 to be gapped at .40 .....they were gapped at .30.
Would/could this be the cause of my idle issues? Also how can i test this engine to know what water temp it should be running at? Im going to reggap these plugs now!

 

[Hammer66]

Re: engine running cool.....poor idle....great wot

Sounds like the thermostat is doing it's job but if you are in doubt it's a quick cheap fix to just replace it. I've seen them stick open intermittantly. I will say that operating your motor at the correct temp as designed and set up by the factory is paramount when trying to tune a carb. So if in doubt replace the thermostat.
Also as stated in a prior post a colder or hotter plug will not affect the operating temperature of your engine. I suggest buying a new set of factory specified plugs. You are now at a good starting point to troubleshoot your idle issue.
One important thing to remember is NEVER assume that the work that was claimed to be done by someone else was done correctly or actually done at all.
Now to start you off. Make sure the engine is running at normal temp with the correct spark plugs. If carb adjustments don't seem to be working I would do a thorough carb cleaning. If you don't feel confident have a competent mechanic do it for you. I would also make sure your fuel filter is new and you are running fresh properly mixed fuel.
Seafoam works great but it won't take the place of a good strip down and clean.
I wouldn't count out a compression issue either. It is a very easy test. You must follow this through in a logical order and not discount any possibilities.
One more thing. Is the idle stop screw properly adjusted? I've seen MANY busy hands fiddle with things for no reason at all or folks thought they were adjusting something else and never bothered to readjust what they were messing with. (I once had a man bring me a chainsaw to replace the starter cord. He tried to help by taking out all the screws to remove the side cover including all three carb adjustment screws.):facepalm:

Good luck!

 

[Hammer66]

Re: engine running cool.....poor idle....great wot

One more thing about operating temperature.
If your water pump is pumping and your thermostat is operating as designed you should not have any "overcooling problems". Most problems are due to bad pumps or blocked or corroded blocks. This causes engines to overheat not overcool.
Are the NGK plugs in the engine OEM? I would recommend using OEM plugs.

 

[yoster]

Re: engine running cool.....poor idle....great wot

the plugs in this boat are gapped incorrectly, i just found out. They are NGK BZ7HS10 to be gapped at .40 .....they were gapped at .30.
Would/could this be the cause of my idle issues? Also how can i test this engine to know what water temp it should be running at? Im going to reggap these plugs now!

You could also try the stock champion plugs. For whatever reason, most people here claim that these OMC's can have some weird issues with non Champion plugs (though I have never personally experienced that). Give the re-gapping a try first and see how it goes.

 

[boobie]

Re: engine running cool.....poor idle....great wot

If you can keep your knuckles on top of the block just before cyl head for over ten seconds when it is idleing it's running to cold. You may want to go back in the thermo hsg and check any seals that are leaking in it. See Shop.Evinrude.com for a good parts break down of it. You can also get a good IR temp test gun at Harbor Freight for around $30.00.

 

[roonie]

Re: engine running cool.....poor idle....great wot

thanks for all the quick responses. I really appreciate this.I will gap these plugs properly as soon as this large system of rain quits over Saskatchewan , Canada. If the gapping does not help i will go out and get some champion plugs and try them. I will be back with a report.

 

[Scubaproh20]

Re: engine running cool.....poor idle....great wot

Its certainly your idle circuit. Bare minimum blow compressed air through the idle mixture screw's passage, and if you can get a piece of small wire to run through the idle jet/ ports. But its possible you have to pop off the welsh plug to clean it. Also replace the seals for the idle mixture screw, it can bleed air into the circuit.

 

[Monte1961]

Re: engine running cool.....poor idle....great wot

I agree with most of the above posts. However, The only way I have found to make sure carb/s are completely clean is to remove from engine and take it all apart including core/welch plugs and allowing it to soak overnight or longer.(Dont soak any plastic). Rinse with fresh water and blowdry any and all holes and ports. Reassemble with a OEM overhaul kit. The core/welch plugs will have to be drilled to remove. USE CAUTION, Only drill through core/welch plug and not in to carb, will make bad JuJu. Good luck and post back.

 

[roonie]

Re: engine running cool.....poor idle....great wot

well...im posting back with a welcomed answer to my woes. I had the muffs on this morning....started her up with new plugs. She started better but still gave the same miss and die. I began to pull off one spark plug wire at a time and low and behold the top plug wire and the second one both gave me a shock down the plier. This with the booty attatched to the plug. As soon as i wiggled the top wire .....bingo....the revs picked up ...the miss went away completely! I am now posting a new question on wire replacement as im not supposed to reply to old threads...ooppps ...i just did

 

[roonie]

Re: engine running cool.....poor idle....great wot

Ive changed my plug wires now and she seems to run perfect. I am going to the lake tomorrow to try her. I had her running with the muffs on and she had to clear out the top piston and ran rough for a wee bit but smoothed out after that. Interesting to note that this running issue only happened at low idle since more spark at high speed would make stronger spark. I no longer have oil/gas mixture coming out of the top carb and all over the air box. It was the top plug wire that was worst. Thanks for all the replies and help folks.Gone fishin!

 

[Hammer66]

Re: engine running cool.....poor idle....great wot

Congrats and enjoy! Glad to hear it was something simple.

 

[roonie]

Re: engine running cool.....poor idle....great wot

thanks...and ...just to add...It all makes sense now. The hand on top the engine felt cool because the top spark plug/piston was not burning fuel....hence the top of the engine was cool.