1974 Evinrude 50hp loss of power at WOT

[jcole]

I've got a 1974 evinrude 50hp that's driving me banannas.

The engine idles fine and when put to wot, boat planes out then engine stalls out after about two minutes.

I've pulled and replaced the reed valves, installed two new coils and plugs, rebuilt the fuel pump, checked the timing and throttle advance and i've cleaned the fuel tanks screens and made sure vents were open while running.

I've replace carb/intake gaskets and needle valve seals.

I've also checked all the wiring, power pack connections, etc and all are secure.

I've set the carb floats per spec (carb upside down, float slightly elevated at far side).

Low speed runs are fine and carbs are adjusted. Problem starts when going to wot.

Last trip to the lake, I had the carb covers off to adjust while son drove boat. I noticed that fuel was spraying from front of carbs. Looked at high speed jets and the both were spraying but seemed like engine getting too much gas. Thottle plates in sync and both wide open at full throttle. Fuel line pump was firm and when squeezed, the engine wanted to stall out. It is a brand new bulb, hose and fuel fittings.

I tried bending the fuel line (about three seconds) to temporarily restrict fuel flow and BAM!. The boat took off and planed out about 38mph, then slowed again. Repeated this and each time the engine would reach wot.

Engine is pumping water fine and not overheating.

I am going to pull the carbs again this week and double check floats and needle valves.

I am thinking that engine is getting too much gas but high speed jets are fixed.

Could it have the wrong jets in the carbs?

Is there someting else I should be checking?

 

[ecoflorida]

I found this old thread by doing a search for "high speed rpm stall"! Sad to see no replies. Or am I just not seeing them?

I have a similar problem on 1996 Tohatsu M50D. Runs great at WOT for about 15-30 seconds then begins to waver over 2-3 seconds then dies. Cranks right back up without problem or need to prime bulb. I did have someone pump bulb in a quick test and still died, but need to duplicate that. (weather was bad and it was rough so could not keep repeating it). I think we have eliminated electrical issues. Stop circuit test was fine and CD unit has been replaced.

I am leaning toward loss of vacuum pressure at high rpm. Possibly reed valve failure at high vac pressure? Where else could high vac pressure cause leak?

 

[racerone]

I doubt it is a reed valve problem.-----But start your own thread / new topic here for some simple trouble shooting.

 

[juno pierrat]

maybe the float drop adjustment, check size of high speed jet, 58D, try float level with carb body, i finally bought the float adjustment tool and when used, "slightly raised" is very slightly raised

 

[ibirish317]

When running watch your primer ball is it going flat? Hope my 2cents helps!