1985 mercury 50hp dies after 30-45 secs at anything over 1/2 throttle

[crazyray78]

new to me engine been setting up several years cleaned and rebuilt carbs with new kits all new fuel pump sectors engine idle good but anything over 1/2 throttle and it will rev good produce good thrust for 30-45 sec then die out. Fuel bulb is tight after it dies out, compress is even on all 4 cylinders but my gauge reads it at 80 psi which is low, any ideas? Have bright blue knel if spark on all 4 cylinders?

 

[Silvertip]

Have you tried a separate (portable) fuel tank and line to eliminate any issues with that. Is the primer bulb installed correctly (arrow pointing toward the engine)?

 

[crazyray78]

1985 mercury 50hp dies out

new to me engine been setting up several years cleaned and rebuilt carbs with new kits all new fuel pump sectors engine idle good but anything over 1/2 throttle and it will rev good produce good thrust for 30-45 sec then die out. Fuel bulb is tight after it dies out, compress is even on all 4 cylinders but my gauge reads it at 80 psi which is low, any ideas? Have bright blue knel if spark on all 4 cylinders?

 

[crazyray78]

Bulb is installed correctly, after it dies out the bulb is still as firm as it was beginning seems if was supply issue that carb bowls would empty out and then have to be refilled but the bulb is solid

 

[jimmbo]

As suggested, try a different Tank and a Different Hose. Is the fuel filter plugged? Does pumping the bulb when the engine is dying, keep it running?

 

[crazyray78]

Will try on another tank, no pumping bulb seems have no effect

 

[crazyray78]

Fuel strainer is clear

 

[crazyray78]

New fuel line and bulb

 

[jimmbo]

Have you tried running it with the gas cap loose?

 

[crazyray78]

Yes had tank cap off entirely

 

[crazyray78]

Would the low compression numbers cause issues with fuel delivery, motor will run at high idle for as long as you like, under a load it will run 30 secs maybe 45 then sounds like drops at least a cylinder then gradually lose rpm and 15 secs later die, pumping bulb seems not help at all, been thru carbs twice not finding anything motor is very temperamental starting in water out of water fires right up, could it have a reed valve issue? Would that cause low signal to fuel pumps under load

 

[jimmbo]

Redo the compression test with another gauge. All plugs out, ground the wires(a spark can ignite the fuel that is being discharged out of the spark plug holes when cranking the engine). Use a fully charged battery of adequate size

 

[crazyray78]

finally got another gauge and even with hot battery and plugs all out getting only 91# on highest about 80# on lowest would these numbers support a smooth running engine? could a bad intake reed cause cause a lack of signal to fuel pumps ? have elimanated tank and external hoses, tried 3 different ones all same results, could the ignition drop out under load? it feels like lose at least a cylinder then gradually lose the others, engine will fire immediately out of water, abit tempermental when in water. would if fuel delivery was a issue could pumping bulb not help it, I at a lose here help

 

[racerone]

Remove the bypass covers and look at the pistons / rings.-----Compression is not encouraging for a good running motor !

 

[Texasmark]

finally got another gauge and even with hot battery and plugs all out getting only 91# on highest about 80# on lowest would these numbers support a smooth running engine? could a bad intake reed cause cause a lack of signal to fuel pumps ? have elimanated tank and external hoses, tried 3 different ones all same results, could the ignition drop out under load? it feels like lose at least a cylinder then gradually lose the others, engine will fire immediately out of water, abit tempermental when in water. would if fuel delivery was a issue could pumping bulb not help it, I at a lose here help

Mercury service manual on a higher hp engine, but none the less similar combustion requirements, says below 120 psi cranking compression expect problems. You are way below that. Any neutral or "muffs" measurements are useless as there is no load on the engine and no HP required from the engine (per se).

 

[crazyray78]

Going to put this engine on back burner and repower boat was a bit skeptical that a fifty was do what I envisioned boat rated for 115hp