omc 120hp stalls under load

[consumidor]

I have a omc 120hp motor, and have had problems getting it to go forward. It runs fine at idle, and revs fine while in neutral. But when i put it in forward or reverse, as soon as i push the throttle, it stalls. I have replaced, points, condenser, cap, rotor, wires, spark plugs, fuel pump, and fuel filter. It has good compression, and timing is correct. I have rebuilt the carbs, and tuned them on land. The engine runs perfect on land as well... does anyone know any reason why this would happen?

 

[vinney]

Re: omc 120hp stalls under load

Shift interrupt switch V

 

[vinney]

Re: omc 120hp stalls under load

I didnt see omc

 

[geriksen]

Re: omc 120hp stalls under load

You need a lower shift cable. The shift interrupt switch is killing the engine. As long as this boat doesnt SX drive. 98? and up.........<br />Have a dealer replace it. You don't want to do that one yourself. There were about twenty recalls and updates on that cable.

 

[consumidor]

Re: omc 120hp stalls under load

sorry, it is '69, i dont think they have shift interrupt on older boats.

 

[BlackSmoke]

Re: omc 120hp stalls under load

Did your carb rebuild include drilling out the plugs and blowing out all passages? Also, have you checked valves/lifters?

 

[coupedeville]

Re: omc 120hp stalls under load

Ignition coil? 4 out of 5 times it's something in the ignition, not fuel system.<br />Does it die as soon as you put it in gear? In other words, will it even idle in gear? If it will, then you can probably discount a shift interuptor.<br />Running in neutral is easy: There isn't a load on the engine.

 

[geriksen]

Re: omc 120hp stalls under load

1969?<br />Guy's, I think this might be an outboard. did you notice he said "carbs"?<br />If this is an outboard, especially a 1969 outboard, you would probably get better answers on the outboard page.

 

[consumidor]

Re: omc 120hp stalls under load

heh... no its not an outboard. It has duel carbs though. The engine runs really rough at idle, would that possibly indicate anything. Its not the electrical system, i know that. Would valves or lifters allow the engine to run with no load, but break down with a load?

 

[911d]

Re: omc 120hp stalls under load

This drive has an electric shift lower unit, the shift wires are prob shorted toghter, causing the lower to lock. The test would be to disconnect one of the shift wires (one with blue collar, and one with green collar at the transom) pick one to disconnect, and shift engine into fwd or reverse (whichever you did not disconnect, green is fwd) and see if it still kills. if it now works, you will have to repair or replace the wiring harness to the lower. This is fairly common on these drives.

 

[consumidor]

Re: omc 120hp stalls under load

sorry, i should probably give more description... i can put it in gear, front and reverse fine, the problem is that when i am trying to accelerate, or after a few seconds after putting the drive in gear, the engine dies. and I'm guessing this is because the engine is not producing enough torque to keep it running when there is an opposing force from the force required to propel the boat. The force being greater, slowing down the engine, until it finally dies. Is it possible this from too lean or too rich condition? or maybe there is something internal that is keeping the engine from producing enough power?

 

[911d]

Re: omc 120hp stalls under load

Ok, then try jumping 12 volts to the + side of the coil and see if this helps. This motor has a ballast resistor that limits current through the points to help the points last longer. Too much resistance in the coil positive circut will cause these kind of symptoms as well. If this cures the problem, trace the circut and repair it, do not run the motor for extended periods with full current to the coil. Running full current can damage the points. Also, make sure your carbs are synched so they open together, at exactly the same time. Finnaly, check for a good stream of fuel from the accel pump discharges in each carb. The Carter RBS carbs on this motor are known for accel pump troubles. Good Luck! <br />Also, what is the condition of the fluid in the upper, and intermediate housings? Maybe a bearing is seizing??

 

[adrew]

Re: omc 120hp stalls under load

sounds lean (vac leak) or accel pumps as 911d said. If running rough at idle, try choking a little and see if it improves.

 

[BlackSmoke]

Re: omc 120hp stalls under load

geriksen, The '69 OMC 120 hp in line four is an I/0 w/ dual Carter RBS Carbs. Sounds like it's got the Stringer electric shift outdrive.<br /><br />consumidor, Simple rebuild on my '69 Carter carbs was inadequate since fuel line trash had gotten into passages. Had to have plugs taken out so all passages could be thoroughly cleaned. Do you have a fuel/water separator in your fuel line? That'll keep old gas tank trash out of the carbs.

 

[geriksen]

Re: omc 120hp stalls under load

Too old for me man. We don't even work on stinger drives, never mind an electric shift. As old as that unit is there is probably more than one problem. It sounds like 911d knows this unit pretty well. Good luck!

 

[911d]

Re: omc 120hp stalls under load

Yeah, Ive seen a few of these! Somewhere there is a group of sadistic ex-omc "engineers" laughing their posteriors off, at this boating joke!! J/K <br />The only other thing that I can come up with, not seeing/hearing the motor myself, is that the exhaust may be restricted. These have a fairly small exhaust elbow, and can get scaled to the point they restrict flow. Also, the exhaust chamber in the intermediate housing is often used for food storage by vermin. One other thought would be a stuck centrifugal advance in the distributor, but no one would do point/cond job without servicing this, Right??

 

[Bondo]

Re: omc 120hp stalls under load

Sounds to me, you should be digging Much deeper into the carbs.... it's running out of gas under load.....

 

[sofasurfer]

Re: omc 120hp stalls under load

This is probably WAY too late but I had the same problem. I had to replace my carbs. That did it. Think I had to give $250 for 2 rebuilt carbs.<br /><br />I also replaced my ballast resistor. If I remember the symptom was that it would fire but as soon as I let off the key it would stall.