Acceleration problem

[Boatnut50]

I am looking at a 120 HP Evinrude. It is about an '86 model and the compression check shows it to be very good, with not more than 4 or 5 pounds difference in any of the cylinders. The problem we are having is that it doesn't want to take the fuel. It idle's well and is ok at slow speed, but doesn't want to get on plane. We have rebuilt the carbs, tried different carbs, checked the reed valves, pumped the bulb, and done everything we could think of. The last time out we finally got mad and just slammed the throttle open and it got up and ran. Now we can usually get it up on plane by slamming the throttle forward, but sometimes it still chokes and dies. Does anyone have an idea what we might check next.

 

[rickdb1boat]

Re: Acceleration problem

Check sparks plugs and be sure they are all firing. Check to be sure the throttle flaps are opening all the way when you put the throttle all the way forward. Could have a sticking throttle cable.

 

[Dhadley]

Re: Acceleration problem

Is the airbox cover on or off?<br /><br />When you say you tried different carbs, did that include the throttle bodys too? Did you try them with their jetting or change the jetting? What spark plugs? How old is the fuel?

 

[Joe Reeves]

Re: Acceleration problem

As per Dhadley's mention of the "Air Box" which I refer to as the carburetor face plate, that item along with the "foam" gasket must absolutely be installed in order for the carburetors to function properly.<br /><br />In cleaning the carburetors, the brass fixed high speed jets, which are located in the bottom center of the float chamber, must be removed and cleaned manually. Any gum build up within those jets will cause the engine to die out when the throttle is applied.<br /><br />Also, a sticking timer base (spark advance) under the flywheel will cause that same problem.<br /><br />The above assumes that you've checked the spark, as well as the compression, with the s/plugs removed and found that it jumps a 7/16" gap with a strong blue lightning like flame.

 

[Boatnut50]

Re: Acceleration problem

This motor has good spark, the throtle flaps are opening, we tried it with the airbox off to check the throtle flaps, and then put it back on, we are using new fuel and new plugs. I was kind of leaning towards something electrical, or maybe a linkage of some kind, that sticking triger sounds interesting.

 

[K Hultgre]

Re: Acceleration problem

As Rick mentioned check the linkage movement. My guess would be a sticky timer base or throttle cable. Engine off, cover open, move the throttle lever from idle to WOT slowly. Now use a piece of chalk and mark where the (linkages, timing base, throttle lever, etc.) stop. Maybe make drawing to help remember. Now as you say "slam" the throttle open and recheck your marks. Might have to try a couple of times to verify it did not stick again.

 

[Dhadley]

Re: Acceleration problem

What kind of new plugs?

 

[rickdb1boat]

Re: Acceleration problem

Hopefully QL77JC4 @ .040

 

[Dhadley]

Re: Acceleration problem

Yes!

 

[y not]

Re: Acceleration problem

Boatnut, After listening to these guys myself and sorting out a similar problem all I can say " IS CHECK THE SPARK AGAIN" my problem turned out to be a small amount of corrosion in the plug lead for one cylinder hidden under the lead boot (plug end)I had checked & double checked everything, but it still turned out to be lack of spark.(intermittant) I have read so many postings from the past over the last couple of days and I dont think I have read anything that doesnt look right & make sense to rectify the problems asked about. so listen read & learn heaps from this helpful crew.

 

[AUGIDAWG]

Re: Acceleration problem

Try advancing the idle timing and see if that helps. If not, put it back to where it was.