1972 18HP Evinrude Idle problem.

[James R]

This motor is like new. I have the history on it. Runs beautifully except for idle. Comps great, good plugs strong sparks, cleaned carb. reset float level at horizontal. Did not have a kit so the only thing in question would be the floatneedle and seat, possibly gasket seals, but they look good. Does not appear to be flooding and the bulb pumps and stays stays hard. Had a new idle seal on hand so no air leaks. Idle needle like new.Takes adjustment ok and responds. Checked Sync and reset per book.
Having found the best carb setting it idles for a while then coughs, rpms drop and then it picks up again. Ocassionally stalls out. Not very consistant. noticed that the bypass tube was split and fuel vapor shot out when it coughed. Resectioned the tube but still the cough. Have ordered a carb kit.
Any ideas please.

 

[steelespike]

Re: 1972 18HP Evinrude Idle problem.

Idle problems can sometimes be caused by bad crank seals.
Excessive oil deposits under the flywheel may indicate an upper seal problem.
The occasional sneeze/cough may indicate idle set too lean.Normal procedure is initial setting one turn out from gently seated.idle speed 700 to 800 rpm.warm in gear un restrained.From best setting turn slightly toward rich.

 

[James R]

Re: 1972 18HP Evinrude Idle problem.

Thanks for the response Steelspike.I can get a sweet spot on the carb mixture. It may be that I dont have it in gear. I have it in a 35gal tub but the motor will throw the water out if in gear. I will fit a new float valve and seat tomorrow and see if that makes any difference. Don't see any seal leakage.I think I am running a little slow although it does not stall when put in gear in the tub. I will bring the idle RPM up a little and see if there is an improvement. May be something and nothing. Needs to be in the pond.
Thanks again.

 

[tashasdaddy]

Re: 1972 18HP Evinrude Idle problem.

read this, http://forums.iboats.com/showthread.php?t=244013

(Carburetor Adjustment - Single S/S Adjustable Needle Valve)
(J. Reeves)

Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.

Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.

Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

Note: As a final double check setting of the slow speed valve(s), if the engine has more than one carburetor, do not attempt to gradually adjust all of the valves/carburetors at the same time. Do one at a time until you hit the above response (die out or spit back), then go on to the next valve/carburetor. It may be necessary to back out "all" of the slow speed adjustable needle valves 1/8 turn before doing this final adjustment due to the fact that one of the valves might be initially set ever so slightly lean.

When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.

 

[F_R]

Re: 1972 18HP Evinrude Idle problem.

That motor falls into the time when they routed the crankcase drain into the upper cylinder, via the bypass cover. That makes the upper cylinder run rich, compared to the lower cylinder. So if you adjust the carburetor to make the upper run decent, the lower will be lean and cough and snort. And the opposite is true, adjust to stop the coughing and the upper will be too rich. I mentioned this in an earlier thread concerning it's 25hp brother.

 

[James R]

Re: 1972 18HP Evinrude Idle problem.

Well I had better Fess up I suppose and look as foolish as I feel. My motor stand is for a 25inch. Had the test fuel tank on the ground. Suzuki's will pump from that height but not the Evinrude. Duh!
Raised the tank and all runs well.
Thanks for all your efforts guys.
Sorry to trouble you.

 

[EARLS BOAT]

Re: 1972 18HP Evinrude Idle problem.

Sounds Like Me!!!

 

[Mas]

Re: 1972 18HP Evinrude Idle problem.

My motor stand is for a 25inch. Had the test fuel tank on the ground. Suzuki's will pump from that height but not the Evinrude.

That's pretty insightful. I learned something there! That solution would have never come across my mind!

MAS