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No RPM under Load - HELP!!! - MD HD Lite 35hp
http://mudmotortalk.com/mmt_v2/viewtopic.php?f=3&t=14070		 Page 1 of 1
Author:  PJDUCK [ Sun Nov 28, 2010 7:48 am ]
Post subject:  No RPM under Load - HELP!!! - MD HD Lite 35hp
With prop in water, the motor just cannot pick up any serious rev and therefore no torque and no speed (I run <10mph now vs. 30mph)...

Here are some other clues/facts :
- motor is 4 years old, <50hrs.
- motor does maintain idle (with lots of exhaust pops!!)
- it does rev good (in neutral or in gear) as long as prop is out of water
- throttle cable is in good shape.
- I shorten & reclamped fuel line (to address possible air leak in line), with no luck.
- Fuel pump was changed by my small engine dealer recently. It apparently took him 2 month to get correct parts from MB and/or Kohler. (I had not taken the boat out for s pin since this last repair)
- Fuel filter was changed by this dealer to a different model than MB's standard. Could that slow down fuel flow?
- Fuel in my tank is kinda old, but treated w/ HEAT & STABIL.

What should I do????

HELP!!!!!!!!!!!!!!!!!!!!!!!! Thanks :)
Author:  craig [ Sun Nov 28, 2010 8:44 am ]
Post subject:  Re: No RPM under Load - HELP!!! - MD HD Lite 35hp
Refer to my post in the "need help asap" thread!
Author:  PJDUCK [ Sun Nov 28, 2010 10:57 am ]
Post subject:  Re: No RPM under Load - HELP!!! - MD HD Lite 35hp
Engine does start when removing either one of the 2 spark plug caps. Also keeps running when either cap is removed. So I must be running on 2 cylinders, I guess?
I also flushed & dried gas tank, and poured in all new fresh gas.

Still, no change....
Author:  craig [ Sun Nov 28, 2010 1:12 pm ]
Post subject:  Re: No RPM under Load - HELP!!! - MD HD Lite 35hp
My next check would be the timing key....located behind the flywheel.
Author:  Team Camo [ Sun Nov 28, 2010 8:06 pm ]
Post subject:  Re: No RPM under Load - HELP!!! - MD HD Lite 35hp
No, wait... Sorry Craig, but this sounds exactly like what mine was doin. Unplug the diodes on the coils. Pull the shroud off the front of the motor to expose the flywheel & coils. Each coil has a small black wire goin to it from the wiring harness. Unplug this wire from both coils & reassemble the front of the motor.
WARNING: you will not be able to use the key or kill switch to shut off the engine when you do this. I have a Mikuni, so I pulled my air filter off & covered the air intake with my hand to shut the motor off. Basically just suffocated the engine.
If you run fine like this, then it's the diodes. The entire wiring harness is like $30. Very simple fix, just a PITA, if ya not lookin for it. Hope this helps. ;)
Author:  craig [ Sun Nov 28, 2010 9:10 pm ]
Post subject:  Re: No RPM under Load - HELP!!! - MD HD Lite 35hp
Rob...no need to be sorry! That's what this is here for! I can only speak of my personal experiences....thanks for that good post! We should have em up and running with the probabilities explained to him!
Author:  Greenhead Crazy [ Sun Nov 28, 2010 9:47 pm ]
Post subject:  Re: No RPM under Load - HELP!!! - MD HD Lite 35hp
My PD just did the same thing about two months ago. I did everything your talking about with the plugs ,wires etc...... it ended up being a broken push rod. it only cost me $100.00 bucks to have it fixed here in town. probelm fixed and has been fine.

Mine was pooping as well with a small amount of smoke coming out of the exhaust..

good luck
Author:  craig [ Sun Nov 28, 2010 10:59 pm ]
Post subject:  Re: No RPM under Load - HELP!!! - MD HD Lite 35hp
Push rod will def. do it!
Author:  Wilson [ Mon Nov 29, 2010 10:02 pm ]
Post subject:  Re: No RPM under Load - HELP!!! - MD HD Lite 35hp
If the diodes are bad it would have killed when he pulled one of the spark plug wires (the one that was still firing). When the diodes go out the engine is only running on one cylinder.
Author:  Team Camo [ Mon Nov 29, 2010 10:26 pm ]
Post subject:  Re: No RPM under Load - HELP!!! - MD HD Lite 35hp
I can tell ya 1st hand, mine didn't when they diodes went out.
Author:  Wilson [ Tue Nov 30, 2010 4:50 am ]
Post subject:  Re: No RPM under Load - HELP!!! - MD HD Lite 35hp
Your's didn't what? It was still running on both cylinders?

Mine have gone out twice and from what I understand, that is what causes the lack of power. The fact that the motor is only running on 1 cylinder. I could easily be wrong, that's just what I was told.
Author:  Team Camo [ Tue Nov 30, 2010 8:16 am ]
Post subject:  Re: No RPM under Load - HELP!!! - MD HD Lite 35hp
It ran like a champ sittin on the trailer, & even in the water (when in neutral), but put it under a load & it fell on it's face. Couldn't even get empty boat on plane. Without a load, couldn't tell anything was wrong with it.
The diodes work with the ignition system & basically ground it out to shut it off, whether by key or kill switch. This is why you can't kill it when they are unplugged.
Author:  Wilson [ Wed Dec 01, 2010 2:43 am ]
Post subject:  Re: No RPM under Load - HELP!!! - MD HD Lite 35hp
Mine did the exact same thing but I think it's because when the diodes go out, only one cylinder is firing.
Author:  PJDUCK [ Sat Dec 11, 2010 5:54 pm ]
Post subject:  Re: No RPM under Load - HELP!!! - MD HD Lite 35hp
MOTOR FIXED!!! :P :P :P
My local small engine repair shop found the problem : carburator was clogged with crap from bad/old gas. They advised me to use STABIL - which I do.... hum hum... They also retuned the high/low throttle cable screw.
Anyway, I ran the rig on the river today and we are going full speeeeeeeeeeeeeeeeeeeeeed! Yipeeeee!

Thks to all :)
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