1990 Evinrude 9.9 hesitation problem

[enegron]

I recently bought a dust covered, but otherwise mint '90 Evinrude 9.9 from a man who bought it new, and used it twice (maybe 5hrs?) in the last 14 years. Last run in ’92. Kept in climate controlled storage for years. Didn’t have an owners manual. Came with 6 gal steel tank.<br /><br />Amazingly, I got it to run without too much trouble. After 10 minutes of rough idling & smoking, it seemed to establish a nice idle & generally run strong. I've had it out six times now, for a total of about 10 hours. Only problem I have is it wants to stall as I accelerate from idle (at about 1/4 throttle). I can avoid this by working the throttle “thru” the stall. It’s a minor annoyance, but once I’m thru it, it runs like a dream.<br /><br />I have put new plugs in it and have changed the lower unit lube. All the old stuff looked good.<br /><br />Engine has a carburetor mixture adjustment knob next to the choke. Original owner had no idea what it was and had it set at the leanest position (that can't be good). Yesterday, I got a genuine OMC service manual on e-bay & just Learned that the purpose of the knob. I experimented today with changing the setting (pointed down at 6:00 instead of 11:00) and had some trouble starting the engine after I had warmed it up well. I also had experimented adjusting the idle adjustment knob at the same time (dummy). <br /><br />One side question I have is: The OMC tank has a radiator type cap, when running should I keep the gas cap turned all the way, or should I open it so it can vent? Could this be my problem?<br /><br />Any ideas on how I can attack this hesitation problem?

 

[ezeke]

Re: 1990 Evinrude 9.9 hesitation problem

As to the cap on the tank, it must be loose to vent the tank. <br /><br />Gently close the lean-rich knob and then turn to rich 1 turn. Adjust 1/8 turn from there, waiting at least 30 seconds.<br /><br />High speed adjustments need to be made under load.<br /><br />Hint: If pulling the choke out slightly when warm increases RPM, you are running too lean.

 

[Solittle]

Re: 1990 Evinrude 9.9 hesitation problem

Lets start out with a BIG WELCOME!!<br /><br />Seems to me that a carb rebuild is in order which should be pretty easy to do with the shop manual.<br /><br />I would also replace the water pump.<br /><br />Let us know how you make out.

 

[BF]

Re: 1990 Evinrude 9.9 hesitation problem

Hiya,<br /><br />Ditto on the water pump... at least change the impeller. Even though it works now, they dry rot and can break without warning... that could lead to a badly overheated engine which could cause many bad things... for $10 and about an hour of your time, changing the impeller is cheap insurance.<br /><br />look here for a great article on your motor (includes instructions for impeller change)...<br /> 9.9/15 hp maintenance article <br /><br />You don't need to loosen the cap to vent OMC tanks... they have a little vent on the connector so when the hose is connected it opens the vent (have a look, there's a little pin that gets pushed in)... If your tank builds vacuum as you run the engine, then the vent clogged.<br /><br />A carb rebuild might be a good idea, or it just could be that the rich/lean low speed mixture adjustment is way outta whack. On my 15 hp (basically same engine as yours), when the engine's cold there is a bog just above idle which depending on how much gas you give, may or may not cause it to stall. If I turn the rich/lean knob towards rich about 1/8 of a turn before taking off, then it's fine (or I can give the choke a brief blip when it hits the boggy spot to get past it). Once the engine warms up, it idles best with the rich/idle turned back that 1/8 of a turn. So my engine anyway is quite sensitive to adjustments of that knob... and likes the mixture a bit on the richer side until it warms up.<br /><br />Hope that helps.... these are great motors by the way!<br /><br />Brent

 

[enegron]

Re: 1990 Evinrude 9.9 hesitation problem

Thanks for the response. I'l give the venting & knob adjustment a try. Failing that, I'll look at a carb rebuild. This is otherwise a great engine. Moves my tin boat about 30mph!<br /><br />ed

 

[enegron]

Re: 1990 Evinrude 9.9 hesitation problem

Fuel tanks are new to me, as my first engine, a 3.5 Tohatsu, has an internal tank.<br /><br />Curious about the mixture knob...I have it pointed at 6:00 or so right now. Impression I have is that most owners have it at 11:00, or as far lean as it will go.<br /><br />Yes, this engine too seems sensitive to adjustments on this.

 

[Chinewalker]

Re: 1990 Evinrude 9.9 hesitation problem

Hi Enegron,<br /> DO NOT pay attention to the position of the pointer on the knob, as the knob is removable and can be placed anywhere on the clock-dial position scale. Gently pry the knob off the shaft of the needle valve. Now, with your fingers, close the valve (clockwise) all the way. Now, turn the valve counter-clockwise 1-full turn. Now, place the knob back on the shaft of the valve with the pointer at dead center of the scale. This will give you plenty of movement in either direction to dial it in properly. Once I get it dialed in where I like it, I will remove the knob once more and re-center it. This way I know when other hands have played with it... <br />- Scott

 

[BF]

Re: 1990 Evinrude 9.9 hesitation problem

I'd be cautious about comparing the knob positions on other engines.. someone may have pulled the knob off and put it back on a different way... I don't remember on that one, but I know that on other engines I have they aren't keyed to only go on one way. Better to just adjust richer and see if it's better or worse etc. If it turns out the correct range for your motor is at the end of the scale, it could mean that either 1) someones put the knob on wrong or 2) you jet is partially clogged and you're compensating by opening more than the normal range. <br /><br />Brent