1981 Evinrude 90HP With throttle Problems

[jrivera7294]

Hello Everyone. Hopefully someone can help me with my problem. I just purchased my first boat which is a 1981 mako17 with a 1981 evinrude 90hp. the Motor idles a bit fast at about 1000RPM. I want to know if there is a way to adjust my throttle. When I throttle down all the way the boat motor is only getting to about 4000rpm. I have taken the cowling cover off while running and manually opened the throttle which quickly launches the boat to a plain and gets the boat up to about 5200 rpm's. How would I adjust the throttle so that i can achieve this kind of throttle response from the stick.

 

[DJ]

Re: 1981 Evinrude 90HP With throttle Problems

The adjustment would be in the cables. The barrels, at the engine end, have thumb wheels to make the adjustments. Don;t touch any adjustments on the engine-yet.

If the cables are original, they may be "stretched".

 

[jrivera7294]

Re: 1981 Evinrude 90HP With throttle Problems

I did play with the thumb wheels a few days ago and ran the boat today. The rmp's went up too much on idle so I backed the thumb screws back out. I am not sure if these are the original cables but they don't look old and warn at all. Is there a way to adjust the tension of the throttle cable?

 

[emdsapmgr]

Re: 1981 Evinrude 90HP With throttle Problems

Disconnect the throttle cable at the engine end. That will release any adjustment issues on the engine and the engine will return to the normal idle setting. When you go to reconnect the throttle cable, you should adjust it (by the thumbwheel) so that it exactly meets the bolt on the engine throttle linkage at that idle setting. Usually this will be the correct setting for idle and full throttle.

 

[jrivera7294]

Re: 1981 Evinrude 90HP With throttle Problems

Should the engine run at an idle of around 750 rpm's with the throttle cable disconnected?

 

[Joe Reeves]

Re: 1981 Evinrude 90HP With throttle Problems

Hopefully those "thumb wheels" you played with weren't the engine linkages but were rather the adjustable plastic "trunion" on the control cables.

The one on the engine linkage has to do with the synchronization of idle timing..... relation of when the throttle butterflies open in relation to the ignition timing. If you moved that one, hopefully you got it back where it belongs.

On a flushette, the idle rpm would be on a 20" shaft model = 1000 rpm, on a 25" shaft model = 1200 rpm. When in the water, the idle rpm would drop to normal.

Regardless of any problem, the very first thing to do is to check the compression and spark. If a problem exists in either of these area, attempting to correct any other problem is futile.

Compression should be 100+ psi and even on all cylinders. What are your readings?

Spark (with the spark plugs removed) should jump a 7/16" gap with a strong blue lightning like flame on all cylinders.... a real SNAP! Does it?

You can approximate the 7/16" gap by using a proper size philips screwdriver inserted into the spark plug boot spring connector, then holding the screwdriver shank that distance from the powerhead. Or, you can build the following if you like.

(Spark Tester - Home Made)
(J. Reeves)

A spark tester can be made with a piece of 1x4 or 1x6, drive a few finishing nails through it, then bend the pointed ends at a right angle. You can then adjust the gap by simply twisting the nail(s). Solder a spark plug wire to one which you can connect to the spark plug boots, and a ground wire of some kind to the other to connect to the powerhead somewhere. Use small alligator clips on the other end of the wires to connect to ground and to the spark plug connector that exists inside of the rubber plug boot.

Using the above, one could easily build a spark tester whereas they could connect 2, 4, 6, or 8 cylinders all at one time. The ground nail being straight up, the others being bent, aimed at the ground nail. A typical 4 cylinder tester follows:


..........X1..........X2

.................X..(grd)

..........X3..........X4

 

[metriccrescentwrench]

Re: 1981 Evinrude 90HP With throttle Problems

ALSO, in addition to what Joe wrote, pull the air box so that you can see the throttle butterflies. Make sure that they're opening all the way when you move the control to full throttle. (DON'T do this with it running!!!!! ) You really need to get a factory service manual, it will walk you through all the adjustments.

I have an '81 Johnson 90 (same engine as yours, different color) and it will be happier if you can prop it to to get around 5800 rpm at WOT. Assuming your engine is running properly you'd want to drop the prop pitch a little bit, you won't loose any top end speed and you'll get better acceleration while putting less strain on the engine.

 

[jrivera7294]

Re: 1981 Evinrude 90HP With throttle Problems

Funny that you mention the prop pitch, because I just purchased a new SS 13.25x15" 4 Blade Solas prop to do just that. I had a 13.25x17 aluminum on there before and noticed that when I was loaded down with 3 people on the boat that the engine would really bog down so I dropped the pitch by 2". This prop really gets it on plane quickly and runs nice and smooth but like I said I have to open throttle by hand in order to really feel it. I know that the motor runs strong its just a matter of making the adjustments so that the throttle cable opens up the throttle all the way.

 

[emdsapmgr]

Re: 1981 Evinrude 90HP With throttle Problems

That engine should idle between 650 and 750 rpm's when it is in gear, and floating normally in the water.

 

[jrivera7294]

Re: 1981 Evinrude 90HP With throttle Problems

What should the RPM's be at WOT?

 

[DJ]

Re: 1981 Evinrude 90HP With throttle Problems

What should the RPM's be at WOT?

Read this-from above.

I have an '81 Johnson 90 (same engine as yours, different color) and it will be happier if you can prop it to to get around 5800 rpm at WOT. Assuming your engine is running properly you'd want to drop the prop pitch a little bit, you won't loose any top end speed and you'll get better acceleration while putting less strain on the engine.
​

 

[jrivera7294]

Re: 1981 Evinrude 90HP With throttle Problems

I'm thinking that I should get engine tuned and replace control cables. Does anyone know what model and size cables I would need?

 

[Fed]

Re: 1981 Evinrude 90HP With throttle Problems

It would be much cheaper to buy the genuine OMC manual then adjust the idle speed and throttle cable properly.
BTW, the throttle cable adjustment has nothing to do with the idle speed.

 

[emoney]

Re: 1981 Evinrude 90HP With throttle Problems

Fed's got a great point because even new cables will have to be right, and its not going to cure the idle speed. If your cables are not froze up, I'd think they're fine.

 

[levi_tsk]

Re: 1981 Evinrude 90HP With throttle Problems

Fed's got a great point because even new cables will have to be right, and its not going to cure the idle speed. If your cables are not froze up, I'd think they're fine.

emoney as DJ said before they can get stretched whic hwould throw the whole thing off ....

 

[jrivera7294]

Re: 1981 Evinrude 90HP With throttle Problems

You guys think that if I purchase the Manual I should be able to make the adjustments myself or should I take it to a mechanic?

 

[levi_tsk]

Re: 1981 Evinrude 90HP With throttle Problems

the adjustments are easy but you have to make sure youve got good cables FIRST and yes with the factory manual an a little mechanical inclination you can fix nearly anything on your motor

 

[ezmobee]

Re: 1981 Evinrude 90HP With throttle Problems

Here's your manual http://cgi.ebay.com/ebaymotors/1981...4477387QQptZBoatQ5fPartsQ5fAccessoriesQ5fGear I'd grab it up quick at that price.

I have that exact motor and that exact manual. Both are great.

 

[jrivera7294]

Re: 1981 Evinrude 90HP With throttle Problems

Ok guys i took the throttle cable off the motor today and found the when i push the control all the way down in reverse the throttle cable extends all the way out as it should. When i did the same in forward i found that the control is not extending the cable all the way out. The problem is definitely in the control itself. Is there anyway to adjust the control so that when i push down the stick the lever inside pushes the throttle cable out completely? Its a bombardier control with no trim control.

 

[jrivera7294]

Re: 1981 Evinrude 90HP With throttle Problems

The model of the control is a bombardier 176375.