1985 115 failure to reach RPMs over 2500

[Ksanthony]

Good morning, I have a new to me 1985 Mercury 115 outboard. It was given to me because of a no spark situation. I was able to track it down to the kill switch being faulty. After replacing that, flushing the fuel, replacing the impeller, checking all the voltage on my sparks I have gotten it started. My problem comes in when I put it in the water. I can not get over 2500 rpms. I have done the time and syncing as described in other post here, it’ll start with a little throttle, once warm it will shift into gear and idle there but once I start to open it up it falls flat on its face. My compression is good, also. I’ve got the timing set at 5 BTDC, and 18BTDC while cranking. I have cleaned the carburetors several times, I haven’t checked my pressure on the fuel pump discharge yet. I have heard it hit 5500 rpms once while adjusting the throttle linkage but lost it quickly. Any ideas??

 

[racerone]

6 cylinder inline ?-------If so is there spark on all 6 leads ?-----And as always post your compression numbers too.

 

[Ksanthony]

Yes inline 6, there is spark on all six. I will have to post exact compression numbers when I get home. I remember they were within tolerance of the tech manual.

 

[jimmbo]

I have heard it hit 5500 rpms once while adjusting the throttle linkage but lost it quickly. Any ideas??

High Rpms like that in Neutral can be Fatal to a 2 stroke. On the muffs the engine can hit those rpms firing on 3 cylinders.

You said you did a link and sync, setting max timing at 18* and pickup Timing at 5*. Did you verify that the carbs are opening fully?

When you checked the spark, was it able to jump a 3/8" gap?

 

[Ksanthony]

Finally got a chance to check the distance. Yes all six can clear 3/8. I have been looking at the carbs and notice they don’t match exactly what the tech manual has. I do not have any built in filters in mine.

 

[jimmbo]

By 85, there were no filters on the top of the fuel bowl, there is either the screen in the fuel pump, or an inline filter, though I think the 1985 engines used the screen.